首页 [高等教育]土木工程专业英语上册翻译苏小卒编同济大学

[高等教育]土木工程专业英语上册翻译苏小卒编同济大学

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[高等教育]土木工程专业英语上册翻译苏小卒编同济大学[高等教育]土木工程专业英语上册翻译苏小卒编同济大学 本课程介绍 在学习普通英语(包括常用词汇和语法结构)的基础上,接合前几个学期已经掌握的关于土 木工程的专业知识,本课程节选了《土木工程专业英语》上册中的内容,涉及建筑材料、材 料力学、结构力学、钢筋混凝土结构、钢结构、测量、土力学、招投标、建筑施工等九个方 面的专业英语知识,从而使大家对土木工程领域内的专业词汇以及科技类文献中的常用句型 有个初步的、基本的学习和了解,为以后查阅专业文献和参与国际交流打好基础。 第三单元 The principal con...

[高等教育]土木工程专业英语上册翻译苏小卒编同济大学
[高等教育]土木工程专业 英语 关于好奇心的名言警句英语高中英语词汇下载高中英语词汇 下载英语衡水体下载小学英语关于形容词和副词的题 上册翻译苏小卒编同济大学 本课程介绍 在学习普通英语(包括常用词汇和语法结构)的基础上,接合前几个学期已经掌握的关于土 木工程的专业知识,本课程节选了《土木工程专业英语》上册中的内容,涉及建筑材料、材 料力学、结构力学、钢筋混凝土结构、钢结构、测量、土力学、招投标、建筑施工等九个方 面的专业英语知识,从而使大家对土木工程领域内的专业词汇以及科技类文献中的常用句型 有个初步的、基本的学习和了解,为以后查阅专业文献和参与国际交流打好基础。 第三单元 The principal construction materials of earlier times were wood and masonry-brick, stone, or tile, and similar materials. The courses or layers(砖层)were bound together with mortar or bitumen, a tarlike substance, or some other binding agent. The Greeks and Romans sometimes used iron rods or clamps to strengthen their building. The columns of the Parthenon in Athens(雅典的帕台农神 庙), for example, have holes drilled(钻孔) in them for iron bars that have now rusted away(锈 蚀殆尽). The Romans also used a natural cement called pozzolana, made from volcanic ash, that became as hard as stone under water. 早期主要的建筑材料是木材和砌体,如砖、石、瓦以及类似的材料。砖层之间 通过砂浆、沥青(一种焦油状的物质)或其他一些粘合剂粘合在一起。希腊人和罗马人有时 用铁条或夹子来加固他们的房屋。例如,雅典的帕台农神庙柱子中曾钻孔以便加入铁条,如 今都已锈蚀殆尽。罗马人也用称作白榴火山灰的天然水泥,它用火山灰制作,在水中会变得 与石头一样坚硬。 Both steel and cement, the two most important construction materials of modern times, were introduced(推广) in the nineteenth century. Steel, basically an alloy of iron (铁合金)and a small amount of carbon, had been made up to that time(到那个时候) by a laborious(繁复的) process that restricted it to such special uses as sword blades(刀刃). After the invention of the Bessemer process (贝塞麦炼钢法)in 1856, steel was available in large quantities at low prices. The enormous advantage of steel is its tensile strength; that is, it does not lose its strength when it is under a calculated degree (适当的) of tension, a force which, as we have seen, tends to (往 往)pull apart many materials. New alloys have further increased the strength of steel and eliminated some of its problems, such as fatigue, which is a tendency for it to weaken as a result of continual changes in stress(连续的应力变化). 作为现代两种最重要的建筑材料,钢材与水泥在十九世纪得到了推广。直到那个时候,钢材 才通过繁复的过程制造出来,基本上是铁合金,并含有少量的碳,因而被限制在一些特殊的 用途如刀刃。在1856年发明了贝塞麦炼钢法后,钢材才得以大量低价获得。钢材巨大的优 势即是它的抗拉强度,也就是当它在适当的拉力下不会失去强度,正如我们所看到的,该力 往往能够将很多材料拉开。新的合金进一步提高了钢材的强度,并消除了一些缺点,如疲劳, 即在连续的应力变化下导致强度减弱的趋势。 Modern cement, called Portland cement, was invented in 1824. It is a mixture of limestone(石灰 石) and clay, which is heated and then ground into a powder(磨成粉末). It is mixed at or near the construction site (施工现场)with sand, aggregate (small stones, crushed rock, or gravel), and water to make concrete. Different proportions of the ingredients (配料)produce concrete with different strength and weight. Concrete is very versatile; it can be poured, pumped, or even sprayed into (喷射成)all kinds of shapes. And whereas steel has great tensile strength, concrete has great strength under compression. Thus, the two substances complement each other(互补). 现代水泥发明于1824年,称为波特兰水泥。它是石灰石和粘土的混合物,加热后 磨成粉末。在或靠近施工现场,将水泥与砂、骨料(小石头、压碎的岩石或砾石)、水混合 而制成混凝土。不同比例的配料会制造出不同强度和重量的混凝土。混凝土的用途很多,可 以浇筑、泵送甚至喷射成各种形状。混凝土具有很大的抗压强度,而钢材具有很大的抗拉强 度。这样,两种材料可以互补。 They also complement each other in another way: they have almost the same rate of contraction and expansion. They therefore can work together in situations where(在„情况下) both compression and tension are factors(主要因素). Steel rods(钢筋) are embedded in(埋入) concrete to make reinforced concrete in concrete beams or structures where tension will develop(出现). Concrete and steel also form such a strong bond - the force that unites(粘合) them - that the steel cannot slip(滑移) with the concrete. Still(还有) another advantage is that steel does not rust in concrete. Acid(酸) corrodes steel, whereas concrete has an alkaline chemical reaction, the opposite of acid. 它们也以另外一种方式互补:它们几乎有相同的收缩率和膨胀率。因此,它们在拉、 压为主要因素时能共同工作。在出现拉力的混凝土梁或结构中,将钢筋埋入混凝土而成钢筋 混凝土。混凝土与钢筋形成如此强大的结合力——这个力将它们粘合在一起——以致于钢筋 在混凝土中不会滑移。还有另一个优势是钢筋在混凝土中不会锈蚀。酸能腐蚀钢筋,而混凝 土会发生碱性的化学反应,与酸相反。 The adoption of structural steel and reinforced concrete caused major changes in traditional construction practices(施工作业). It was no longer necessary to use thick walls of stone or brick for multistory buildings, and it became much simpler to build fire-resistant floors(防火地面). Both these changes served to(有利于) reduce the cost of construction. It also became possible to erect(建造)buildings with greater heights and longer spans. 结构钢与钢筋混凝土的采用使传统的施工作业发生了明显的变化。对多层建筑,再 也没必要采用厚的石墙或砖墙,且施工防火地面变为容易得多。这些变化有利于降低建筑的 成本。它也使建造高度更高和跨度更大的建筑物成为可能。 Since the weight of modern structures is carried(承受) by the steel or concrete frame, the walls do not support the building. They have become curtain walls, which keep out the weather and let in light. In the earlier steel or concrete frame building, the curtain walls were generally made of masonry; they had the solid look of bearing walls(承重墙). Today, however, curtain walls are often made of lightweight materials such as glass, aluminum, or plastic, in various combinations. 由于现代结构的重量由钢或混凝土框架承受,墙体不再支承建筑物。它们成为幕墙, 将日晒风吹雨打阻挡在外,而让光线进入。在较早的钢或混凝土框架建筑中,幕墙一般由砌 体构成;它们具有承重墙的结实外观。但是今天,幕墙通常由轻质材料组成,如玻璃、铝或 塑料,并形成不同的组合。 Another advance in steel construction(结构) is the method of fastening together(连在一起) the beams. For many years the standard method was riveting. A rivet is a bolt with a head that looks like a blunt screw(圆头螺丝钉) without threads(螺纹). It is heated, placed in holes through the pieces of steel(钢构件), and a second head is formed at the other end by hammering(锤击)it to hold it in place(固定就位). Riveting has now largely been replaced by welding, the joining together of pieces of steel by melting(熔化) a steel material between them under high heat. 钢结构中的另一个进步是梁的连接方式。在很多年里,连接的 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 方式是铆接。铆 钉是个有头的螺栓,看上去象个没有螺纹的圆头螺丝钉。铆钉加热后穿过钢构件之间的孔洞, 并通过锤击另一端而形成第二个铆钉头,从而将其固定就位。如今铆接已大量地被焊接所替 代,钢构件间的连接通过在高热下熔化它们之间的钢材料(即焊条)进行。 Prestressed concrete is an improved form of reinforcement(加强方法). Steel rods are bent into the shapes to give them the necessary degree of tensile strength. They are then used to prestress (对..预加应力)concrete, usually by one of two different methods. The first is to leave channels in a concrete beam that correspond to(相应于) the shapes of the steel rods. When the rods are run through the channels, they are then bonded to the concrete by filling the channels with grout, a thin mortar or binding agent. In the other (and more common) method, the prestressed steel rods are placed in the lower part of a form(模板) that corresponds to the shape of the finished structure(成品结构), and the concrete is poured around them. Prestressed concrete uses less steel and less concrete. Because it is so economical, it is a highly desirable(非常理想) material. 预应力混凝土是加强法的改进形式。将钢筋弯成一定的形状以使它们具有必要的抗拉强度, 然后用该钢筋对混凝土施加预应力,通常可采用两种不同方法中的任何一种。第一种方法是 在混凝土梁中按钢筋的形状留下孔道,当钢筋穿过孔道后,通过在孔道内灌注薄砂浆(一种 稀薄的砂浆或粘合剂)将钢筋与混凝土粘结在一起。另一种(更常用的)方法是将预应力钢 筋置于按成品结构的形状设置的模板的较低部位,然后将混凝土倒入(模板)而包围着钢筋。 预应力混凝土使用了较少的钢筋和混凝土,由于它是如此的经济,因此是一种非常理想的材 料。 Prestressed concrete has made it possible to develop(建造) buildings with unusual shapes, like some of the modern sports arenas, with large space unbroken by any obstructing supports(阻碍的 支撑物). The uses for this relatively new structural method are constantly being developed(不断 地扩大). 预应力混凝土使建造独特形状的建筑物成为可能,象一些现代的运动场,它具有不 受任何支撑物阻挡视线的大空间。这种较新的结构方法的使用正在不断地被扩大。 The current tendency is to develop(采用) lighter materials, aluminum, for example, weighs much less than steel but has many of the same properties. Aluminum beams have already been used for bridge construction and for the framework of a few buildings. 目前的趋势是采用较轻的材料。例如,铝的重量比钢轻得多,但具有很多相同 的性能。铝材梁已经用于桥梁建筑和一些建筑的框架。 Lightweight concretes, another example, are now rapidly developing(发展) throughout the world. They are used for their thermal insulation(绝热性). The three types are illustrated below(举例说 明如下): (a) Concretes made with lightweight aggregates; (b) Aerated concretes (US gas concretes) foamed(起泡) by whisking(搅拌)or by some chemical process during casting; (c) No-fines concretes. 另一个例子是轻质混凝土,如今已在全世界快速地发展,因它们的绝热性而被 采用,其三种类型举例说明如下:(a)轻质骨料制成的混凝土;(b)通过浇筑时搅拌或一些化 学方法起泡而成的加气混凝土(US加气混凝土);(c)无细骨料混凝土。 All three types are used for their insulating properties(绝热性), mainly in housing, where they give high(非常) comfort in cold climates and a low cost of cooling(降温成本)in hot climates. In housing, the relative weakness of lightweight concrete walls is unimportant, but it matters(有重 大关系) in roof slabs, floor slabs and beams. 这三种类型的混凝土都是由于它们的绝热性而被使用,主要用于房屋,使其在 寒冷的气候中非常舒服,在炎热的气候中降温的成本不高。在房屋中,墙采用较薄弱的轻质 混凝土不重要,但是屋面板、楼面板和梁(采用轻质混凝土)则有重大关系。 In some locations, some lightweight aggregates cost little more than(几乎等于) the best dense (致密) aggregates and a large number of (大量) floor slabs have therefore been built of lightweight aggregate concrete purely for its weight saving, with no thought of(没考虑) its insulation value. 在某些地区,一些轻质骨料的费用几乎等于最致密的骨料,因此大量的楼面板 采用轻骨料混凝土制作纯粹是节约重量,而没考虑它的绝热价值。 The lightweight aggregate reduces the floor dead load(恒载) by about 20 per cent resulting in(导致)considerable savings in the floor(楼盖结构) steel in every floor and the roof, as well as in the column steel and (less) in the foundations. One London contractor(承包商)prefers to use lightweight aggregate because it gives him the same weight reduction in the floor slab as the use of hollow tiles, with simpler organization and therefore higher speed and profit. The insulation value of the lightweight aggregate is only important in the roof insulation, which is greatly improved(改进). 轻质骨料使楼面的恒载减少了约20%,因而大量的节约了每层楼面以及屋面的楼 盖结构中的钢材和柱子与基础中(较少)的钢材使用量。一位伦敦的承包商宁愿使用轻质骨 料,因为这使楼面板上减少的重量与用空心砖相同,且组织更简单,因而速度和利润更高。 轻质骨料的绝热价值只在屋面绝热时显得重要,它已被大大地改进了。 作业练习 通过两篇 Reading Materials 的学习,进一步了解建筑材料中最常用的混凝土材料的一些特 点、种类和性能等,从而更多地掌握一些专业词汇和句法。 教学目标 了解构件(主要为梁)的设计过程 了解单轴应力与多轴应力对失效理论的影响 熟悉材料力学中涉及的专业词汇 熟悉科技类文献常用句型 熟悉in general、usually、frequently的不同含义与 be referred to as、be known as、that is、be defined as、in other words 等的用法 Introduction 介绍 Mechanics of Materials deals with(研究)the response of various bodies, usually called members(构件), to applied forces(施加力). In Mechanics of Engineering Materials the members have shapes that either exist in actual structures or are being considered for their suitability(根据其需 要)as parts of proposed(拟建的)engineering structures. The materials in the members have properties that are characteristic of commonly used(常用的)engineering materials such as steel, aluminum, concrete, and wood. 材料力学用以研究不同物体(通常称为构件)对施加力的响应。在工程材料力 学中,构件的形状可以是实际结构中存在的,也可以根据其需要而进行考虑(设计),作为 拟建工程结构的部件。构件中材料的性能即是常用的工程材料如钢材、铝材、混凝土和木材 的特性。 As you can see already from the variety of materials, forces, and shapes mentioned, Mechanics of Engineering Materials is of interest to(对..有价值)all fields of engineering. The engineer uses the principles of Mechanics of Materials to determine if the material properties and the dimensions of a member are adequate to(足以)ensure that it can carry its loads safely and without excessive distortion. In general(通常), then, we are interested in both the safe load that a member can carry and the associated(相关的)deformation. Engineering design would be a simple process if the designer could take into consideration(考虑)the loads and the mechanical properties of the materials, manipulate(利用)an equation, and arrive at(得到)suitable dimensions. Design is seldom that simple. Usually(通常), on the basis of(根据)experience, the designer selects a trial(试算) member and then does an analysis to see if that member meets the specified requirements. Frequently(常常), it does not and then a new trial member is selected and the analysis repeated. This design cycle(设计周期) continues until a satisfactory solution is obtained. The number of cycles(循环次数) required to find an acceptable design diminishes as the designer gains experience. 正如你已经从提到的各种各样的材料、力和形状所看到的,工程材料力学对所有的工程领域 都有价值。工程师利用材料力学的原理来确定是否该材料的性能和构件尺寸足以保证它能安 全地承受荷载且没有过多的变形。通常,我们关心的是构件能承受的安全荷载及其相应的变 形。如果设计者能通过考虑荷载和材料的力学性能,并利用公式得到合适的构件尺寸,那么 工程设计将是一个简单的过程。然而设计很少那么简单。通常,根据经验,设计者选择一个 试算构件,然后进行分析,看它是否满足规定的要求。它常常不会满足要求,则再选择一个 新的试算构件,再进行分析。这样的设计不断重复,直至得到一个满意的结果。当设计师拥 有一定的经验后,为得到一个可接受的设计所需要的循环次数会减少。 Design of Axially Loaded Members 轴向力构件的设计 To give you some insight into (使..有一些了解)the design cycle, an extremely simple member will be dealt with first. That member is a prismatic bar with a force, P, acting along its longitudinal axis in the direction(纵轴向)such that it tends to elongate the bar. Such a force is referred to as(称为)an axial tensile load(轴向拉力), and we can readily imagine it trying to(努力..)pull the fibers apart and to cause failure on a transverse plane(横向平面). It is safe to assume that all fibers of the bar, in regions remote from(远离)the point of application of the load, are being pulled apart with the same load intensity(荷载强度). With this assumption, the load intensity or stress is uniform on a transverse plane and is given by when P is in(以..为单位)Newtons metre (N/m2), which is by definition(根据定义)Pascals (Pa). 为了使你对设计周期有一些了解,首先研究一个非常简单的构件。构件是个棱形的杆件,其 上沿着它的纵轴向作用一个力P,这样往往使杆件在该方向上伸长。这样的力称为轴向拉力, 我们能容易地想象它在努力地将纤维拉开,导致横向平面的破坏。安全地假定杆件的所有纤 维在远离荷载施加点的区域以相同的荷载强度被拉开。在此假定下,荷载强度或应力在横向 平面上是均匀的,为 当P的单位为牛顿、A的单位为平方米时,应力σ的单位为牛顿每平方米(N/m2),根据定 义为帕斯卡(Pa)。 For a given axial load and given dimensions, the stress can be calculated from (4-1) and compared with(与..相比)the stress that can be safely carried by the material. The safe stress, known as(称 为)the design stress or allowable stress(许用应力), is determined by tests performed on material made to(按照) the same specifications as the part being considered. A safety factor(安全系数), frequently imposed by a legally established code(法规), is applied to the strength, as determined by tests, to give the allowable stress. Th factor. 对已知的轴向力和(构件)尺寸,可根据公式(4-1)计算出应力,并与材料能安全承受的 应力作比较。安全应力,称为设计应力或许用应力,它是通过对材料的试验来确定的,该(试 验)材料按照与所考虑(验算)的杆件相同的规范制作。根据法规规定,通常对试验所确定 的强度考虑安全系数后得到许用应力。许用应力 为 这里,为材料失效(失效在下文有定义)时的应力,而n为安全系数。 Before approving(核准)trial dimensions, the designer makes certain(确信)that the design is safe by determining that the inequality(不等式) is satisfied. The inequality is usually more convenient in the form 不等式常常以更合适的形式出现,即 在核准试算的尺寸之前,设计者通过确定不等式成立而确信设计的安全,即 It might at first(起先)seem that the designer would always dimension(选定..的尺寸)the cross section(横截面) so that the stress would exactly equal the allowable stress. However, it may be very costly to produce parts that have nonstandard sizes, so it is usually more economical to waste some material by selecting the next(接近的)larger standard size above that required by the allowable stress. Departure from(背离)standard sizes is justified(合理的) in cases where the penalty(不利后果)for excess weight is very severe, as in aircraft(航天器)or space-ship(宇 宙飞船)design. 起先似乎设计者总是在选定横截面的尺寸,以使应力恰好等于许用应力。但是,生 产非标准尺寸部件的成本可能很高,因此,通常人们会选择比按许用应力要求的尺寸大一些 的标准尺寸部件,这样尽管浪费了一些材料,但总体上更经济。但不选择标准尺寸的做法在 诸如航天器和宇宙飞船的设计中证明是合理的,因为多余重量产生的不利后果是很严重的。 Design of Beams 梁的设计 Up to this point(至此)we have looked at(考虑)the beam problem as a problem in analysis; that is(即), for a given set of loads, span, and cross section we have been calculating the stress. The more commonly encountered problem is to select a standard section, or design a member, for a given span and loads without exceeding a certain allowable stress. Under some conditions the allowable stress may be dependent upon the dimensions and shape of the cross section, in which case the selection of the member becomes more difficult. For the present(暂时)we will take the allowable stress as though(似乎)it depends only on the strength of the material and the safety factor. 至此,我们已经考虑了梁的问 快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题 而进行了(问题)分析,即对给定的一组荷载、跨度和横截 面,我们已经计算了应力。更常遇到的问题是在不超过某个许用应力下对一个给定的跨度和 荷载选择一个(构件的)标准截面,或设计一个构件。在某些条件下,许用应力可能依赖于 横截面的尺寸和形状,这种情况下的构件选择会变得比较困难。暂时我们将采用许用应力法, 似乎它只取决于材料的强度和安全系数。 A trial member will be acceptable(合格)when the stress is equal to, or less than, the allowable stress, that is, if For design purposes this inequality is more useful in the form In the usual design process the maximum bending moment is taken from(取自于)the bending moment diagram(弯矩图) and the allowable stress is determined (quite frequently in accordance with(根据)the rules of some legally constituted code) from standard strength tests in combination with(与..结合)a safety factor. The right-hand side of (4-6) is then known, and it remains(仍然 是) to select or design a member that will satisfy the inequality. When a standard section is to be used, the tables(表格)could be searched until a member is found such that the combination of I and c satisfies (4-6). This takes more time than is really necessary, since the tables also provide the value of I/c for each member under the heading(标题)S, the section modulus(截面模量). 当试算构件的应力等于或小于许用应力时,也就是说,如果 在通常的设计过程中,最大的弯距从弯距图上取得,而许用应力通过标准强度试验并考虑安 全系数后确定(往往是根据一些法规的规则)。这样,已知式(4-6)右手边的值,则仍然是 选择或设计构件以满足该不等式。当使用标准截面时可以查找表格,直至找到的构件其I和 c值的组合能满足式(4-6)。这样花费的时间比实际需要的多,因为表格中在截面模量S的 标题下也提供了每一个构件的I/c的值。 试算构件即为合格。根据设计的需要,(上述)不等式以下列形式出现更有用,即 That is, the section modulus is defined as(定义为) To select a member, the S column(列) is consulted(查阅) and any member that satisfies (4-8) could be used. The members with very high values of S will obviously be understressed(应力不 足的)and wasteful of material. The best design, if there are no other constraints, will be that which satisfies (4-8) with the minimum amount of material. With tabulated values of S available it is much more convenient to use (4-6) in the form The smallest acceptable S does not necessarily coincide with(符合)the most economical member. To select the lightest and most economical standard section, the listed values of mass should be examined to find the lightest member with an acceptable S. The problem becomes much more complex if built-up(组合)member is being designed because its cost will depend upon the combined costs of web plate, angles and cover plates as well as fabrication(装配)costs so that the lightest member is not necessarily the most economical. 截面模量定义为 为选择构件而查阅S这一列,则任何满足式(4-8)的构件都可采用。显而易见,对S值很 高的构件,其应力是不足的,并浪费了材料。如果没有其他的限制,最好的设计将是以最少 的材料满足式(4-8)。能接受的最小的S值不必是最经济的构件。为了选择最轻和最经济的 标准截面,应检查列出的质量值,以找到能接受的S值下的最轻构件。如果在设计一个组 合构件时,则问题变得复杂得多,因为它的费用将依赖于腹板、角钢和盖板的费用以及装配 的费用,因此,最轻的构件未必是最经济的构件。 根据表格中得到的值S,将式(4-6)以下列形式使用要方便得多,即 Deflections Due to Bending 弯曲挠度 The main purpose of this chapter(本节) was to develop(提出)the flexure(屈曲)formulas, and to provide some experience in applying them. Statically indeterminate(超静定)cases were encountered and some insight(认识) gained as to(就..)the difficulty and importance of this category of problem. 本节的主要目的是提出屈曲公式,并在运用公式时提供一些经验。当遇到超静 定的情况时,就此类问题的难点和重点获得一些认识。 Superposition(叠加法)was presented(提出) as the preferred(优先的)method for solving certain problems. However, becoming familiar with(熟悉)superposition was more important than finding solutions to the problems(问题的答案) because superposition has application in many areas of stress analysis and will be used frequently in our future studies. 为解决某些问题,叠加法作为优先的方法被提出。但是,熟悉叠加法远比找到 问题的答案重要,因为叠加法已经用于应力分析的很多领域,而且,在我们今后的研究中还 会经常使用。 Moment-area(弯距图面积法)was found to be a convenient method for solving various problems. It is a method that becomes quite complicated and requires further development(展开) when more advanced structures are encountered. At the present stage it is sufficient for you to be acquainted with(了解)the fundamentals(基本原理)of the method. Deflection of long-radius (长半径) curved beams was introduced(引入)to illustrate the power of the principles underlying(构成..的基础)the moment-area method and so that you would appreciate(知道)the differences between straight and curved beams. 为解决不同的问题,发现弯距图面积法是一种很便利的方法。但当遇到更先进 的结构时,此法会变得非常复杂,需要进一步地展开。对你来说在目前阶段了解此法的基本 原理已经足够了。引入长半径曲梁的挠度来举例说明构成弯距图面积法基础的原理的功效, 使你能知道直梁与曲梁之间的区别。 This chapter afforded an opportunity to become familiar with singularity functions (奇异函数), and you have seen that certain problems can be greatly simplified by their use. It must be appreciated(意识到)that merely an introduction to the topic has been given; there is much more to learned by those who have a special interest. To illustrate a serious limitation(缺陷) at our present stage, we can express distributed loads (分布荷载) that are variable and are intermittent, but we cannot write a load function for concentrated loads. If we had taken the next step and dealt with the concentrated load, we would have encountered the source of the expression(表达式) “singularity function”, but having regard for(考虑)the scope of this book we have stopped short of(达不到)that step. 本节使你熟悉了奇异函数,并发现通过利用它们能大大地简化某些问题。但必须意识到仅仅 是介绍了题目,对那些有特殊兴趣的人还有很多要学。我们可以表示变化的、间断的分布荷 载,但不能写出集中荷载的荷载函数,说明了在我们目前阶段(该函数)还存在着严重的缺 陷。如果我们进入下一步去研究集中荷载,便会遇到奇异函数表达式的来源,但是考虑到本 书的范围,我们不再进入那一步。 Failure Theories 失效理论 In the design of a member subjected to a uniaxial(单轴的) load, the stress was compared with the stress to cause failure in test specimens(试件)that had also been subjected to uniaxial load. This is the simplest of all design problems; the method is quite adequate(合适的), since the nature(性能)of the loads and the stresses in the test and in the part being designed are identical. However, we soon encounter cases where the member being designed is not so simple and the stresses are not uniaxial; consider, for example, the stresses in the web of a beam or in a pressure vessel(压力容器). In these cases we know that the stress is two-dimensional(两向的)or biaxial and it may, in other cases, be three-dimensional, or triaxial. For a structure having biaxial or triaxial stresses, how should we check the safety of the design? The most obvious way would be to conduct tests(进行) in which specimens are stressed(受力) to failure in the same multiaxial(多轴的)manner as in the structure; the allowable multiaxial stress then be determined by the application of an adequate safety factor. However, this would require a group of tests for every new set of multiaxial stresses that occurred in design. Such tests are difficult to perform, and the cost of performing them in the required numbers would be prohibitive. Consequently, we need a theory by which the results of the standard uniaxial test can be used to predict(预测)the failure of a part made of the same material when the stresses are multiaxial. In other words(换句话说), we need a failure theory. 在设计承受轴向力的构件时,将其应力与导致同样承受轴向力的试验样本(试件)失效的应 力相比。这是所有设计问题中最简单的;该法是非常合适的,因为试验和设计中的荷载和应 力性质是完全相同的。但是,不久我们便会遇到正在设计的构件不是那么简单,其应力也不 是单轴向的;例如,考虑梁的腹板应力或压力容器中的应力。在这些情况下,我们知道其应 力是两向的或两轴的,而在其他情况下可能是三向或三轴的。对一个有着两轴或三轴应力的 结构,我们应该如何检查它的设计安全性,最显然的办法是进行试验,即试件以与结构相同 的多轴受力方式失效;然后运用适当的安全系数确定许用的多轴应力。但是,对设计中出现 的每组新的多轴应力都将需要一组试验。这样的试验很难进行,而且以需要的数量进行试验 的费用也是禁止的。因此,我们需要一个理论,根据它可以通过利用标准单轴试验的结果来 预测同样材料制作的构件在承受多轴应力时的失效。换句话说,我们需要一个失效理论。 To illustrate the need for a failure theory, let us consider a cylindrical pressure vessel. To avoid unnecessary complications, we will consider that all welds(焊缝)are 100% efficient and that the walls(容器壁)are thin. Under internal pressure the main stresses(主应力) are circumferential and longitudinal, and it was implied(认为)in an earlier case that only the circumferential stress, because it is larger than the longitudinal stress, needs to be considered in judging the adequacy of the design. In this approach we tacitly(默认)assumed that the maximum stress could be treated as(看作为)a uniaxial stress and that it alone determined the safety of the design. The longitudinal stress was not considered although it may, without our knowledge(在我们的知识之外), have had an influence on strength. It happens that our approach in this case is acceptable, but, in a biaxial state of stress, the second stress is not always inconsequential(不重要)and an understanding of failure theory is necessary in order to avoid making some serious errors. 为了举例说明需要一个失效理论,让我们考虑一个圆柱形的压力容器。为避免不必要的复杂, 我们认为焊缝完全有效,容器壁是薄的。在内部压力下,主应力是环向和纵向的,由于环向 应力比纵向应力大,因此,在一个较早的例子中认为只有环向应力需要在判断设计的适用性 时加以考虑。在这个方法中,我们默认地假定最大的应力(即环向应力)可看作为单轴应力, 并由它单独地确定设计的安全性。尽管在我们的知识以外,纵向应力可能会对强度有影响, 但不被考虑。正巧,在这种情况下我们的方法能被接受,但是,在两轴应力状态下,第二种 应力不总是不重要的,为了避免造成一些严重的错误,对失效理论的理解是必要的。 Unfortunately, as we will discover, no single theory(单一理论) will be found to apply in all cases; for example, theories that are satisfactory for ductile materials are not acceptable for brittle materials. We will also find that one of the best theories is too complex for everyday use and that most designers prefer(更喜欢)a simpler theory that introduces(产生)a small but safeside(安 全的)error. 很不幸,正如我们将发现的,没有找到一个单一的理论能运用于所有的状况, 例如,满足延性材料的理论,脆性材料不能接受。我们也将发现每天在使用一个最好的理论 太复杂了,多数设计者更喜欢用一个会产生小而安全的错误但较简单的理论。 In developing(提出)the various failure theories, we cannot avoid three-dimensional effects, but we will treat(讨论)only those cases in which one of the stresses is zero, thus avoiding complications that would tend to obscure(使..模糊不清)the important part of the theories. This is not a serious limitation, since in engineering practice(工程实践) most problems are reduced to (简化为)the biaxial stress state for design. When shear stresses(剪应力)occur along with(与.. 一起)normal stresses(正应力), the principal stresses(主应力)are determined. Thus, for practical (实用的)purposes, we need to consider failure in a material subjected to two nonzero(非零) normal stresses while the third normal stress is zero. For ease in(为了便于..)designating (称 呼)those principal stresses we will use numerical subscripts(数字下标) 在提出不同的失效理论时,我们不能避免三向的影响,但我们将只讨论其中某一个应力为零 的情况,因而避免了复杂性,因它往往使理论的重要部分模糊不清。这不是个严重的缺陷, 因为在工程实践中,多数问题在设计时被简化为两轴应力状态。当剪应力与正应力一起存在 时,主应力便被确定。这样,为了实用的目的,我们需要考虑承受两个非零正应力而第三个 正应力为零的材料的失效。为了便于称呼那些主应力,我们采用数字下标: 和作为 非零应力,而为零。 We cannot discuss failure theory until we have defined failure. We might take the obvious definition that a material has failed when it has broken into(分为)two or more parts. However, it has already been pointed out that in most applications a member would be unserviceable(不再适 用)due to excessive distortion long before(早在)it actually ruptured(断裂). Consequently, we will relate failure to yielding and consider that a material has failed when it will no longer return to(恢复)its original(最初的)shape upon(一旦)release of the loads. In a simple tensile test (拉伸试验)we would then say that a ductile material has failed when the material begins to yield. Then f either tension or compression. 在我们定义了失效后才能对其进行讨论。我们可能会下一个明显的定义,即当材料分成两部 分或更多时失效。但是,在多数应用中已经被指出,一个构件早在它实际断裂之前由于过分 的变形而不再适用。因此,我们将失效与屈服联系起来,并认为一旦荷载解除而材料不再恢 复到其最初的形状时即为失效。在一个简单的拉伸试验中,我们可以说当延性材料开始屈服 时即已失效。对单轴应力而言,当应力达到屈服应力(不管拉或压)时即为失效。 Brittle materials fail by a different mechanism and will be discussed after the theories for ductile materials have been presented(介绍). 脆性材料由于不同的机理而失效,这将在介绍延性材料的理论之后进行讨论。 作业练习 通过一篇 Reading Material 的学习,进一步了解材料力学的发展史、安全系数的求解、纯弯 梁的应变分析、超静定梁的分析等。 Unit 5 第五单元 Structural Analysis 结构分析 教学目标 了解结构分析的假定和几种方法 了解结构分析中运用的几个定理 熟悉结构力学中的专业词汇 熟悉科技类文献中的常用句型 熟悉as a consequence、 as a result、for these reasons、therefore 以及as a consequence of、as a result of 的含义;state 的不同用法;relate to、relate„.to、be related to 的区别;be equal to、 be equated to、equal 的用法; with respect to、regarding、considering、as to 的用法 A structure consists of(由..组成)a series of connected parts used to support loads. Notable(显 著的) examples include buildings, bridges, towers, tanks, and dams. The process(过程)of creating any of these structures requires planning(规划), analysis, design, and construction(施 工). Structural analysis consists of (包括)a variety of mathematical procedures(数学程序) for determining such quantities as the member forces and various structural displacements(位移) as a structure responds to its loads. Estimating realistic loads for the structure considering(根据) its use and location is often a part of structural analysis. 结构由一系列相连的用以支撑荷载的构件组成。显著的例子包括建筑、桥梁、 塔、水箱和大坝等。建造这些结构中的任何一个的过程需要规划、分析、设计和建造。结构 分析包括各种各样的数学程序以确定诸如当一个结构对荷载有响应时构件的力和不同结构 位移的大小。根据结构的使用和位置来估计它的实际荷载经常是结构分析的一部分。 Only two assumptions are made regarding(关于)the materials used in the structures of this chapter. First, the material has a linear stress-strain relationship(线性的应力-应变关系). Second, there is no difference in the material behavior when stressed in tension vis-a-vis(与..相比) compression. The frames and trusses studied are plane structural systems(平面结构体系). It will be assumed that there is adequate bracing perpendicular to(垂直于)the plane so that no member will fail due to an elastic instability(弹性失稳). The very important consideration regarding such instability will be left for the specific(具体的)design course. All structures are assumed to undergo only small deformations as they are loaded. As a consequence(因此)we assume no change in the position or direction of a force as a result of (由 于)structural deflections(变位). Finally, since linear elastic materials and small displacement are assumed, the principle of superposition will apply in all cases. Thus the displacements or internal forces that arise from two different forces systems applied one at a time(一次一个)may be added algebraically(几何相加)to determine the structure’s response when both system(s) are applied simultaneously. 关于本章结构中所用的材料只作了两点假设。首先,材料具有线性的应力应变关系。其次, 材料的性能在受拉和受压时没有区别。研究的框架和桁架是平面结构体系。假定垂直于平面 的方向有足够的支撑,因而构件不会因为弹性失稳而失效。一个非常重要的关于这种失稳的 考虑留待具体的设计过程。假定所有的结构在它们加荷时只经历小的变形。因此,我们假定 当结构变位时荷载的位置与方向不变。最后,因为假定了线弹性材料和小位移,叠加原理将 适用于所有的情况。这样当两种不同的力系同时施加时,可以由不同的力系一次施加一个引 起的位移或内力几何相加来确定结构的响应。 In the real sense(真正意义上)an exact analysis of a structure can never be carried out since estimates always have to be made of the loadings and the strength of the materials composing(构 成)the structure. Furthermore, points of application(作用点)for the loadings must also be estimated. It is important, therefore, that the structural engineers develop(形成)the ability to model(模拟)or idealize(使..理想化)a structure so that he or she can perform a practical force analysis of the members. 真正意义上对一个结构准确的分析是永远也不可能进行的,因为总是不得不估 计荷载和构成结构的材料的强度。而且,必须估计荷载的作用点。因此,结构工程师有能力 模拟一个结构或使其理想化很重要,这样,他或她能对构件进行实际的力的分析。 Structural members are joined together in various ways depending on the intent(意图)of the designer. The two types of joints most often specified(规定的)are the pin connection and the fixed joint(节点). A pin-connected joint allows some freedom for slight(轻微)rotation, whereas the fixed joint allows no relative rotation between the connected members. In reality, however, all connections exhibit(显现)some stiffness toward joint rotations, owing to friction(摩擦)and material behavior. When selecting a particular model for each support(支座)or joint, the engineer must be aware of how the assumptions will affect the actual performance(运行)of the member and whether the assumptions are reasonable for the structural design. In reality, all structural supports actually exert(产生)distributed surface loads(面荷载)on their contacting members. The resultants(合力) of these load distributions are often idealized as the concentrated forces(集 中力)and moments, since the surface area (表面积)over which the distributed load acts is considerably smaller than the total surface area of the connecting members. The ability to reduce an actual structure to(将..简化为)an idealized form can only be gained by experience. In engineering practice, if it becomes doubtful(不明确)as to how to model a structure or transfer the loads to the members, it is best to consider several idealized structures and loadings and then design the actual structure so that it can resist(抵抗)the loadings in all the idealized models. 结构构件根据设计者的意图采用不同的方式连在一起。最常规定的两种节点是铰接节点和固 定节点。铰接节点允许有一些轻微的转动自由,而固定节点不允许相连的构件有相对的转动。 但是,事实上由于摩擦和材料的特性使所有的连接对节点的转动显现出一些刚度。当为每一 个支座或节点选择一个特定的模型时,工程师必须知道该假设将如何影响构件的实际运行, 以及该假设是否对结构的设计是合理的。实际上,所有的结构支座在它们接触的构件上产生 分布的面荷载。这些荷载分布的合力常常理想化为集中力和弯矩,因为分布荷载作用的表面 面积比相连的构件的总的表面面积小很多。将一个实际的结构简化成一种理想的形式的能力 只有通过经验才能获得。在工程实践中,如果就怎样模拟一个结构或将荷载传递给构件变得 难以确定时,最好考虑几个理想的结构和荷载,然后设计实际的结构,使它在所有理想的模 型中都能抵抗荷载。 It may be recalled(回想)from statics that a structure or one of its members is in equilibrium(处 于平衡) when it maintains a balance of force and moment. When all the forces in a structure can be determined strictly from these equations, the structure is referred to as statically determinate(静 定的). Structures having more unknown forces than available equilibrium equations(平衡方程) are called statically indeterminate. As a general rule, a structure can be identified as(确定)being either statically determinate or statically indeterminate by drawing free-body diagrams(隔离体 图)of all its members, or selective parts of its members, and then comparing the total number of unknown reactive force and moment components(分量)with the total number of available equilibrium equations. 从静力学可以回想起当一个结构或它的一个构件维持力和弯矩的平衡时即处于平衡状态。当 一个结构中所有的力能严格地根据这些方程式来确定,该结构称为静定的。如果结构上未知 的力比能得到的平衡方程多时称为超静定结构。作为一般的规律,一个结构可以通过画出所 有构件或经选择的部分构件的隔离体图,然后比较未知的反力和弯矩的分量总数目与可用的 平衡方程总数目是否相等来确定其是静定结构还是超静定结构。 In particular, if a structure is statically indeterminate, the additional equations(附加方程)needed to solve for(求解)the unknown reactions(反力)are obtained by relating the applied loads and reactions to the displacement or slope(转角)at different points on the structure. These equations, which are referred to as compatibility equations(相容性方程或协调方程), must be equal in number to the degree of indeterminacy(不确定次数)of the structure. Compatibility equations involve(涉及)the geometric and physical properties of the structure. 特别地,如果一个结构是超静定的,可以通过建立作用力和反力与结构不同点 上的位移或转角的关系来得到用以求解未知反力所需的附加方程。这些称为相容性方程的方 程式在数量上必须等于结构的不确定次数。相容性方程涉及结构的几何和物理性能。 There are two fundamental methods of analysis for trusses: the method of joints and the method of sections. Both start with(从..着手)a free-body diagram of the truss as a whole(基本上), from which the equilibrium equations are written and solved for the support reactions(支座反力). 有两种分析桁架的基本方法:节点法和截面法。两种方法基本上都从桁架的隔 离体图着手,根据它可以写出平衡方程并求解支座反力。 The method of joints: After the support reactions have been found, a joint is selected that has no more than(不超过)two members connecting for which the axial forces are unknown. The free-body diagram of that joint is drawn, the forces are summed(合计)in two directions, and each sum is equated to(等于)zero. When drawing the free-body diagram, it is a good idea to assume that the unknown forces are tensions and to show(表示)them so on the free-body diagram by their exerting a pull on(对..施加拉力)the joint. When this is assumed, the resulting sign(符号) of the unknowns when evaluated(计算)will match(符合)the conventional(习惯的)+ for tension and – for compression. Once a joint has been analyzed, its members become knowns, and adjacent joints(相邻节点), which might have had three or more unknowns, can then be solved since some of these unknowns have become knowns. This process(过程)continues from joint to joint, each time selecting a joint whose number of unknown members does not exceed 2. 节点法:求出支座反力后,选择一个节点其上连接着轴向力未知的构件不超过两根。画出节 点的隔离体图,将力在两个方向上进行合计,每个方向(力)的合计等于零。当画出隔离体 图时,有个好主意是假定未知力是拉力,并在隔离体图上通过对该节点施加一个拉力来表示。 这样假定后,未知力计算结果的符号将与习惯的正为拉力负为压力相符。一旦一个节点已经 被分析,其上的构件成为已知构件,相邻的节点可能曾经有三个或更多的未知力,但因为其 中的一些已经成为已知,因此也能求出。这个过程从一个节点到另一个节点连续进行,每次 选择的节点其上未知构件(力)的数量不超过两根。 Almost all truss systems are configured(装配)so that analysis using the method of joints must begin at one end and proceed(继续)joint by joint toward the other end. If it is necessary to evaluate the forces carried by a member located(位于)some distance from the ends, the method of joints requires the calculation of the forces in many members before the desired one is reached. The method of sections provides a means(方法)for a direct calculation in these cases. After the support reactions have been calculated the truss is cut through(切开)(analytically分析上) so that one part of the truss is completely severed from the rest. When this is done, no more than three unknown members should be cut. If possible(如果可能)the cut(切口)should pass through the member or members whose internal forces are to be found. A free-body diagram of the part of the truss on one side of(在..一边)this section is drawn, and the internal forces are found through the equilibrium equations. Since the system of forces(力系)on the free-body diagram is a plane non-concurrent(非共点)force system, three equilibrium equations may be written and solved for the three unknowns. 几乎所有的桁架体系是装配的,因此采用节点法进行的分析必须从一个端点开始,并一个节 点连着一个节点地朝另一个端点继续进行。如果有必要计算位于端部一定距离的构件上的 力,节点法需要在到达这根要求(计算)的构件之前计算很多构件中的力。在这些情况下截 面法提供了一个直接计算的方法。当求出支座反力后,桁架(在分析上)被切开,从而一部 分桁架同其余部分完全分离。当这样切开时,应该切出不超过三个构件的力是未知的。如果 可能,切口应穿过将要求解内力的构件。画出在截面一边的桁架部分的隔离体图,并通过平 衡方程式求解内力。由于隔离体图上的力系是平面非共点的,因而可以写出三个平衡方程式 并求出三个未知力。 Influence lines(影响线)have important application for(应用)the design of structures that resist large live loads(活荷载). An influence line represents(代表)the variation of either the reaction, shear, moment, or deflection at a specific (特定的)point in a member as concentrated force moves over the member. Once this line is constructed(作图), one can tell at a glance(一眼便知) where a live load should be placed on the structure so that it creates(引起)the greatest influence at the specified point. Furthermore, the magnitude(大小)of the associated (相关的)reaction, shear, moment, or deflection at the point can then be calculated from the ordinates(纵坐标)of the influence-line diagram. For these reasons(因此), influence lines play an important part in the design of bridges, industrial crane rails(吊车轨道), conveyors, and other structures where loads move across their span(全 长). Although the procedure(步骤)for constructing an influence line is rather basic(基本的), one should clearly be aware of the difference between constructing an influence line and constructing a shear or moment diagram. Influence lines represent the effect of a moving load only at a specified point on a member, whereas shear and moment diagrams represent the effect of fixed loads at all points along the axis of the member. 影响线在设计抵抗大量活荷载的结构时有着重要的应用。一根影响线代表着当集中力在构件 上移动时构件上一个特定点的反力、剪力、弯矩或挠度的变化。一旦画出这根线,任何人一 眼便知活荷载应该置于结构的哪个位置才能对这个特定的点引起最大的影响。而且,这点上 相关的反力、剪力、弯矩或挠度可从影响线图的纵坐标上计算出来。因此,影响线在桥梁、 工业吊车轨道、输送机和其它有荷载在整个结构长度上移动的结构设计中扮演着重要的角 色。虽然画出一条影响线的步骤是相当基本的,但任何人应该清楚地意识到画一条影响线与 画一条剪力或弯矩图的区别。影响线只代表着移动荷载对构件上特定点的影响,而剪力和弯 矩图代表固定荷载对沿着构件轴线的所有点的影响。 Deflections of structures can occur from various sources(原因), such as loads, temperature, fabrication errors, or settlement. In design, deflections must be limited in order to prevent cracking of attached(附属的) brittle materials such as concrete or plaster (石膏) . Furthermore, a structure must not vibrate or deflect(变位)severely in order to “appear” safe for its occupants(居住 者). More important, though(然而), deflections at specified points in a structure must be computed if one is to analyze statically indeterminate structures. We often determine the elastic deflections of a structure using both geometrical and energy methods. Also, the methods of double integration(双重积分)are used. The geometrical methods include the moment-area theorems(弯 矩图面积定理)and the conjugate-beam method(共轭梁法), and the energy methods to be considered are based on virtual work(虚功)and Castigliano’s theorem(卡氏最小功定理). Each of these methods has particular advantages or disadvantages. 结构的挠度可以因不同的原因而发生,如荷载、温度、制造错误或沉降。设计中,挠度必须 加以限制以阻止附属的脆性材料如混凝土或石膏的开裂。而且,为了向居住者显示安全性, 结构不能严重地振动或变位。而更重要的是如果有人要分析超静定结构,必须计算出结构中 规定点的挠度。我们通常采用几何法和能量法来确定结构的弹性挠度。也采用双重积分法。 几何法包括弯矩图面积定理和共轭梁法,而考虑的能量法是基于虚功定理和卡式最小功定 理。每一种方法都有其特别的优缺点。 We can determine the equation of the elastic curve by integration of equation d2v / dx2 = M / EI. Solution of this equation requires two successive(连续的)integrations to obtain the deflection v of the elastic curve. For each integration, it is necessary to introduce(引入)a “constant of integration”(积分常数), and then solve for the constants to obtain a unique solution(唯一解) for a particular(特定的)problem. It should be realized that the method of double integration is suitable only for elastic deflections(变位)such that the beam’s slope is very small. Furthermore, the method considers only deflections due to bending. 我们可以通过对方程d2v / dx2 = M / EI的积分来确定弹性曲线的方程。该方程 的求解需要两个连续的积分,以获得弹性曲线的挠度v。对每次积分,有必要引入积分常数, 求出该常数以获得一个特定问题的唯一解。应该了解到双重积分法只适合于弹性变位,因而 梁的转角是非常小的。而且,该法只考虑了由于弯曲引起的挠度。 The initial ideas(最初的概念)for the two moment-area theorems were developed(提出)by Otto Mohr and later stated formally(正式确定)by Charles E. Greene in 1872. These theorems provide a semi-graphical (半图解)technique for determining the slope of the elastic curve and its deflection due to bending. They are particularly advantageous(有利)when used to solve problems involving beams especially those subjected to a series of concentrated loadings or having segments(段)with different moment of inertia(惯性矩). Theorem 1: The change in slope(转 角变化)between any two points on the elastic curve equals the area of the M / EI diagram between these two points. Theorem 2: The deviation(偏差)of the tangent(正切)at point B on the elastic curve with respect to(相对于)the tangent at point A equals the “moment” of the M / EI diagram between the two points A and B computed about point A (the point on the elastic curve), where(这里)the deviation tA/B is to be determined. 最初的关于两个弯矩图面积定理的概念是由Otto Mohr提出,后来由Charles E. Greene在 1872年正式加以确定。这些定理为确定弹性曲线由于弯曲引起的转角和挠度提供了半图解 的方法。当用以解决包括梁在内的问题,特别是那些承受一组集中加载的梁或有着不同惯性 矩的梁段时,它们(指弯矩图面积定理)是特别得有利。定理1:弹性曲线上任何两点之间 转角的变化等于这两点之间的M / EI图的面积。定理2:弹性曲线上B点的正切相对于A 点的正切的偏差等于点A与点B之间的M / EI图对A点(该点在弹性曲线上)的矩,这里 偏差tA/B将被确定。 The conjugate-beam method was first presented(提出)by Otto Mohr in 1860. Essentially(本质 上), it requires the same amount of computation(计算量)as the moment-area theorems to determine a beam’s slope or deflection; however, this method relies only on the principles of statics and hence its application will be more familiar(常见). The basis for the method comes from(来自于)the similarity(相似性)between both dV/dx = -- a beam’s internal shear and moment to its applied M/EI, which relate the slope and deflection of its elastic curve to the internal moment. 共轭梁法首先在1860年由Otto Mohr提出。本质上说,它与弯矩图面积定理 一样在确定梁的转角或挠度上需要相同的计算量;但是这种方法只依赖于静力学的原理,因 此,它的应用更常见。该法的基础来自于dV/dx=-和d2M/dx2=-之间的相似性,它将梁 的内部剪力和弯矩与它施加的荷载联系起来,而和d2y/dx2 = M/EI将弹性曲 线的转角和挠度与内部弯矩联系起来。 Note that the shear V compares with(与..对应) EI diagram. To make use of this comparison we will consider a beam having the same length as the real beam, but referred to here as the “conjugate beam”. 注意剪力V与转角相对应,弯矩M与位移y相对应,而外力的强度与M/EI图下 的面积相对应。为了利用这些对应,我们将考虑一根与实际梁一样长的梁。但是这里称为共 轭梁。 In general, though(然而), remember that if the real support allows a slope, the conjugate support must develop(产生)a shear; and if the real support allows a displacement, the conjugate support must develop a moment, note that the conjugate beam is “loaded” with the M/EI diagram, in order to conform to(与..一致)the load on the real beam. We can therefore state(陈述)two theorems related to the conjugate beam, namely(即), Theorem 1: The slope at a point in the real beam is equal to the shear at the corresponding point(相应点)in conjugate beam. Theorem 2: The displacement of a point in the real beam is equal to the moment at the corresponding point in the conjugate beam. 然而通常要记住如果实际的支座允许一个转角,共轭的支座必须产生一个剪力;如果实际的 支座允许一个位移,共轭的支座必须产生一个弯矩,注意共轭梁用M/EI图来加荷,以便与 实际梁上的荷载一致。因此,我们可以陈述与共轭梁相关的两种定理,即,定理1:实际梁 上某一点的转角等于共轭梁上相应点的剪力。定理2:实际梁上某一点的位移等于共轭梁上 相应点的弯矩。 For more complicated loadings or for structures such as trusses and frame, it is suggested(建议) that energy methods be used for the computation. All energy methods are based on the conservation of energy principle(能量守恒原则), which states(规定)that the work(功)done by all the external forces acting on a structure, Ue, is transformed into(转化为)internal work or strain energy(应变能)UI, which is developed(形成)when the structure deforms(变形). 对于较复杂的荷载或结构如桁架和框架,建议应该采用能量法来计算。所有的 能量法是基于能量守恒原则,它规定了作用在结构上的所有外力作的功Ue转化成内部功或 结构变形时形成的应变能UI 。 The principle of virtual work was developed by John Bernoulli in 1717 and is sometimes referred to as the unit-load method(单位荷载法). It provides a general means(一般方法)of obtaining the displacement and slope at a point on a structure, be it(无论是)a beam, frame, or truss. Before developing the principle of virtual work, it is necessary to make some general statements(一般规 定)regarding the principle of work and energy. 虚功原理在1717年由John Bernoulli提出,有时称为单位荷载法。它提供了获 得结构上某一点的位移和转角的一般的方法,不管该结构是梁、框架还是桁架。在提出虚功 原理之前,关于功和能量的原理有必要作些一般规定。 If we take(取)a deformable(可变形)structure of any shape or size and apply a series of external loads P to it, it will cause internal loads u at points throughout the structure. It is necessary that the external and internal loads be related by the equation of equilibrium. As a consequence of(通过) will occur at each point of internal load u. 如果我们取一个任何形状或尺寸的可变形结构,并对它施加一组外力P,它将导致整个 结构上的点产生内力u。有必要通过平衡方程将内外力联系起来。通过这些荷载,外部的位 移发生在荷载P作用处,而内部位移发生在内力u所处的每个点。 In general, these displacements do not have to be elastic, and they may not be related to(与..有关) the loads; however, the external and internal displacements must be related by the compatibility of the displacements. In other words, if the external displacements are known, the corresponding internal displacements are uniquely defined(唯一确定). In general, then, the principle of work and energy states(表述): (5-1) Work of External Loads = Work of Internal Loads 一般来说,这些位移不必是弹性的,它们可能与荷载无关。但是外部位移与内部位移必须通 过位移协调联系起来。换句话说,如果已知外部位移,则相应的内部位移可惟一的确定。通 常,功和能量原理表述为 (5-1) 外力功=内力功 Based on this concept, we will now develop(提出)the principle of virtual work so that it can be used to determine the displacement of a point on a structure. To do this, we will consider the structure (or body) to be of arbitrary(任意)shape as shown in Fig. 5-1-(b). Suppose it is necessary It is to be understood that these loads cause no movement of the supports; in general, however, they can strain(使..产生应变) the material beyond the elastic limit. 基于这个概念,现在我们将提出虚功原理,以便用以确定结构上某一点的位移。 为此,我们考虑图5-1-(b)显示的具有任意形状的结构或物体。假定有必要确定由实际荷载 P1、P2 和 P3 引起的A点的位移。可以被理解为这些荷载不引起支座的移动;但是一般而 言,它们能使材料的应变超过弹性极限。 Since no external load ac determined by first placing on the body a “virtual” load such that this force P’ acts in the same -1-(a). For convenience(方便起见), which will be apparent(显而易见) later, we will choose P’ to have a “unit” magnitude(单位值), that is P’ = 1. The term “virtual” is used to describe the load, since it is imaginary(想象的)and does not actually exist as part of the real loading. The unit load (P’) does, however, create an internal virtual load u in a representative(典型的)element or fiber of the body, as shown in Fig.5-1-(a). 由于没有外力作用在物体的A点以及的方向上,则位移可以通过在物体上先设置 一个虚力,即如图5-1-(a)中作用一个与方向相同的力P’来确定。为了方便起见(后面会 显而易见),我们选择P’有一个单位值,即P’=1。用术语“虚”来描述荷载,因为它是想象 的,非实际存在的真实荷载的部分。但是,单位荷载P’在物体的典型单元或纤维中产生了 一个内部虚力u,如图5-1-(a)所示。 Here it is required that P’ and u be related by the equation of equilibrium. As a result of(通过) these loadings, the body and the element will each undergo a virtual displacement due to the load P’, although we will not be concerned with(关心)its magnitude. Once the virtual loadings are applied and then the body is subjected to the real loads P1, P2, and P3, Fig.5-1-(b), point A is 这里要求P’和u通过平衡方程联系起来。通过这些(虚)荷载,物体和单元各自由于 荷载P’而经历一个虚位移,尽管我们不会关心它的数值。一旦施加虚荷载,然后物体承受 图5-1-(b)中的实际荷载P1、P2和P3,则点A产生位移值,导致单元发生变形dL。 As a result(因此), the external virtual force P’ and internal virtual load u “ride along” by(乘上) (分别地)e is equal to the internal virtual work done on all the elements of the body, we can write the virtual work equation as (5-2) 因此,外部虚力P’和内部虚力u分别与和dL“乘在一起”,因此在物体上形成外部虚 功,在单元上形成内部虚功。了解到外部虚功等于对物体所有单元作的内部虚功,我们可以 写出虚功方程 (5-2) Where P’=1=external virtual unit load acting in the dire u = internal virtual load acting on the element in the direction of dL dL = internal deformation of the element caused by the real loads 这里,P’等于1,也等于作用在方向上的外部虚单位力; u等于以dL方向作用在单元上的内部虚力; 等于真实荷载引起的外部位移; dL等于真实荷载引起的单元的内部变形。 可以看到通过选择P’=1能直接得到解,因为。 In a similar manner, if the rotational displacement(转动位移)or slope(转角)of the tangent at a point on a structure is to be determined, a virtual couple moment(力偶矩)M’ having a “unit” magnitude is applied at the point. As a consequence(因此), this couple moment cause a virtual load in one of the element of the body. Assuming that the real loads deform(使..变形)the element - This method for applying the principle of virtual work is often referred to as the method of virtual forces(虚力法), since a virtual force is applied resulting in the calculation of a real displacement. The equation of virtual work in this case represents a compatibility requirement for the structure. 以相似的方法,如果要确定结构上某一点切线的转动位移或转角,可在该点上 施加一个虚的单位力偶矩M’。因此,力偶矩在物体的某一单元中形成一个虚力。假定实际 的力使单元的变形值为dL,则转角可从虚功方程中得到。运用虚功 原理的方法通常称为虚力法,因为施加虚力能计算出实际的位移。在这种情况下虚功方程代 表着对结构的协调要求。 Although not important here, realize(意识)that we can also apply the principle of virtual work as a method of virtual displacements(虚位移). In this case virtual displacements are imposed on(强 加于)the structure, while the structure is subjected to real loadings. This method can be used to determine a force on or in a structure, so that the equation of virtual work is then expressed as an equilibrium requirement. 了解到我们也能运用虚功原理形成虚位移法,尽管在这儿不太重要。这种情况下,虚位 移强加于结构,而结构承受实际的荷载。该法能用以确定结构上或结构中的力,因此虚功方 程表示为平衡要求。 In 1879 Alberto Castigliano, an Italian railroad engineer, published a book in which he outline(概 述)a method for determining the deflection or slope at a point in a structure, be it a truss, beam, or frame. This method, which is referred to as Castigliano’s second theorem(卡氏第二定理), or the method of least work(最小功法), applies only to structures that have constant temperature(恒 温), unyielding(不易弯曲)supports, and linear elastic material response. 1879年Alberto Castigliano,一个意大利的铁路工程师,出版了一本书,书中他 概述了确定结构(无论是桁架、梁或框架)中某一点的挠度或转角的方法。这种称为卡氏第 二定理或最小功法的方法仅应用于具有恒温、支座不易弯曲和材料线弹性响应的结构中。 If the displacement of a point is to be determined, the theorem states(表明)that it is equal to the first partial derivative(一阶偏导数)of the strain energy in the structure with respect to (关于) a force acting at a point and in the direction of displacement. In a similar manner, the slope at a point in a structure is equal to the first partial derivative of the strain energy in the structure with respect to a couple moment acting at the point and in the direction of rotation. 如果要确定某一点的位移,该定理表明位移等于结构中的应变能对于作用在该点并沿该 位移方向的力的一阶偏导数。以相似的方式,结构上某一点的转角等于结构中的应变能对于 作用在该点并沿该转角方向的力偶的一阶偏导数。 The derivation(推导)of the theorem requires that only conservative forces(保守力)be considered for the analysis. These forces do work that is independent of(与..无关)the path and therefore create no energy loss(能量损失). Since forces causing a linear elastic response are conservative, the theorem is restricted to linear elastic behavior of the material. This is unlike the method of virtual force, which applies to both elastic and inelastic behavior. 定理的推导要求分析时只考虑保守力。这些力作功与路径无关,因此不造成能量的损失。 由于引起线弹性响应的力是保守的,因此该定理(在运用时)被限制在材料的线弹性状态。 它不象虚力法可以运用于弹性和非弹性状态。 When analyzing any indeterminate structure, it is necessary to satisfy equilibrium, compatibility, and force-displacement requirements for the structure. Equilibrium is satisfied when the reactive forces hold the structure at rest(保持结构静止), and compatibility is satisfied when the various segments(部分)of the structure fit together(配合在一起)without intentional(故意的)breaks or overlaps(断裂或重叠). The force displacement requirements depend upon the way the material responds, which in this chapter we have assumed linear-elastic response. In general there are two different ways to satisfy these requirements when analyzing a statically indeterminate structure: the force or flexibility method(柔度法), and the stiffness or displacement method. 当分析任何不确定的结构时,有必要满足结构的平衡、协调和力-位移要求。当反力保持结 构的静止时满足平衡(要求),当结构中不同的部分配合在一起而没有故意地断开或重叠时 满足协调(要求)。力-位移要求依赖于材料响应的途径,在本篇我们已经假定为线弹性响应。 当分析一个超静定结构时,一般有两种不同的方法来满足这些要求:力法或柔度法以及刚度 法或位移法。 The force method was originally(最初地)developed by James Clerk Maxwell in 1864 and later refined(提炼)by Otto Mohr and Heinrich Muller-Breslau. This method was one of the first available(最早采用)for the analysis of statically indeterminate structures. As suggested(提示) by the name, the force method consists of writing equations that satisfy the compatibility and force-displacement requirements for the structure and involve(涉及)redundant forces(冗余力) as the unknowns. The coefficients(系数)of these unknowns are called flexibility coefficients. Since compatibility forms(形成)the basis for this method, it has sometimes been referred to as the compatibility method or the method of consistent displacements(位移协调法). The redundant forces are determined by satisfying the equilibrium requirements for the structure. The fundamental principles(基本原理)involved in (涉及)applying this method are easy to understand and develop(阐述). 力法最初由James Clerk Maxwell 在1864提出,后由Otto Mohr和Heinrich Muller-Breslau 加以提炼。该法是最早可采用的分析超静定结构的方法之一。正如其名称所提示的,力法包 括写出满足结构协调要求和力-位移要求的方程以及涉及未知冗余力的方程。这些未知力的 系数称为柔度系数。由于协调性形成了这个方法的基础,它有时被称为协调法或位移协调法。 通过满足结构的平衡要求来确定冗余力。涉及该法运用的基本原理是很容易理解和阐述的。 When Marxwell developed the force method of analysis, he also published(发表)a theorem that relates(使..互相关联) the flexibility coefficients of any two points on an elastic structure – be it a truss, a beam, or a frame. This theorem is referred to as the theorem of reciprocal displacements(位移互等定理)and may be stated as follows(陈述如下): The displacement of a point B on a structure due to a unit load acting at point A is equal to the displacement of point A when the unit load is acting at point B, that is fBA = fAB. The theorem also applies for reciprocal rotations(转角互等). Furthermore, using a unit force and unit couple moment, applied at separate(分开的)points on the structure, we may also state: The rotation in radians(以弧度为单位)at point B on a structure due to a unit load acting at point A is equal to the displacement at point A when a unit couple moment is acting at point B. 当Marxwell提出力法分析时,他也发表了使弹性结构上任意两点的柔度系数相关的定理- 无论是桁架、梁或框架。该定理称为位移互等定理,可以陈述如下:由作用在结构上A点 的单位力引起B点的位移等于当单位力作用在B点时引起的A点的位移,即fBA = fAB。 该定理也适用于转角互等。而且,将单位力和单位力偶矩施加在结构上不同的点,我们也可 以陈述为:由作用在结构上A点的单位力引起B点的转角(单位为弧度)等于当单位力偶 矩作用在B点时引起的A点的位移。 The displacement / stiffness method of analysis is based on first writing force-displacement relations(关系式)for the members and then satisfying the equilibrium requirements for the structure. In this case the unknowns(未知量)in the equations are displacements and their coefficients are called stiffness coefficients. Once the displacements are obtained, the forces are determined from the compatibility and force-displacement equations. 位移法或刚度法的分析是基于最初写出的构件的力-位移关系式,并且要满足结 构的平衡要求。在这种情况下,方程式中的未知量是位移,而它们的系数称为刚度系数。一 旦求得位移,就可从协调方程和力-位移方程中确定力。 Early in the 20th century slope deflection(转角位移法)was the most popular(流行的)method in use for analyzing statically indeterminate frames. It was developed by Professor G.A. Maney and began its reign of popularity(开始盛行)almost immediately after its publication(发表)in 1915. Fifteen years later the moment distribution method(弯矩分配法)was introduced and there began a period of spirited professional competition (激烈的专业竞争)over the merits(优势) of the two methods, with moment distribution eventually emerging as the “winner”, primarily because of its speed and simplicity. But the competition has not ended. Today, although moment distribution continues as(依然作为)the more popular method, there remain many contemporary (同时代的)engineers who prefer slope deflection. 早在20世纪,转角位移法是用以分析超静定框架最流行的方法。它由G.A. Maney教授提出, 并在1915年发表后几乎迅速开始盛行。15年后弯矩分配法被采用,并在一段时期内开始了 对两种方法的优势展开的激烈的专业竞争,弯矩分配法最终以胜者出现,主要是由于它的速 度和简单。但是竞争没有结束。今天,尽管弯矩分配法依然作为较流行的方法,仍有很多同 时代的工程师较喜欢用转角位移法。 They contend(辩解)that in performing a slope deflection analysis the engineer can acquire a better “intuitive feel”(直觉)for the structure than the use of any other method. More significant(重要的), though, slope deflection has gained renewed(重新)importance(重要地位)with the advent(到来)of the computer, serving as(作为)the central method(重要方法) used for structural analysis software. Slope deflection focuses on(着重于)individual members, their loads, and certain conditions at their ends. 他们辩解在进行转角位移分析时能比在使用任何其它的方法中获得对结构更好的直觉。 然而更重要的是,转角位移法由于计算机的到来已经重新获得了重要地位,作为用于结构分 析软件的重要方法。转角位移法着重于单个构件、作用于它们的荷载和端部的某些条件。 In using this method, simultaneous equations(联立方程)are written and solved that have displacements, rather than forces or moments, as unknowns. It employs a simple sign convention(符号约定): all variables(变量)related to a member are positive(正的)if they are clockwise (顺时针的). The complete slope deflection equations for MAB and MBA are the superpositions -(5-3) -(5-4) 在采用该法时,写出联立方程并求解位移的未知量,而不是力或弯矩作为未知量。它采用了 简单的符号约定:所有与构件有关的变量如果是顺时针则为正。对MAB和MBA ,完整的转 角位移方程为四个部分的叠加:和荷载。因此 -6EI/L2 (5-3) -(5-4) Where MAB and MBA are clockwise end moments B that matches(符合)a clockwise rotation of AB FEM is referred to as fixed end moment. 这里, MAB和MBA为顺时针的端部弯矩; 和为顺时针的端部转角; 是端部A相对于B的线位移,符合 AB的 顺时针转动; FEM 称为固定端弯矩。 Analysis by slope deflection begins with use of above equations to write separate expressions for the end moments at each end of each member. Equilibrium is then imposed(利用)using moment of equations(方程组)is produced that has the end displacements as unknowns. When solved simultaneously(联立求解), the resulting displacements(得到的位移) are substituted in(代入)the slope deflection equations, giving the end moments. 转角位移法的分析从采用上述方程分别写出每个构件在每一端的端部弯矩表达式着手。 然后利用平衡,即采用节点转动未知量时的弯矩平衡和构件有未知量时的横向力平衡。 形成以端部位移为未知量的方程组。当联立求解时,将求解得到的位移代入转角位移方程, 得到端部弯矩。 The method of analyzing beams and frames using moment distribution was developed by Hardy Cross, a professor of civil engineering at the University of Illinois. At the time this method was first published(公布)in 1932, it attracted immediate attention, and it has been recognized as one of the most notable(显著的) advances in structural analysis during the twentieth century. Moment distribution is a method of successive approximations(逐次近似计算法)that may be carried out (实现)any desired degree of accuracy(精度). Essentially(本质上), the method begins by(首先)assuming each joint of structure is fixed. Then, by unlocking and locking(解 开与锁住)each joint in succession(连续地), the internal moments at the joints are “distributed” (分配)and balanced until the joints have rotated to their final or nearly final positions. 采用弯矩分配法分析梁和框架的方法由Illinois大学的土木工程教授Hardy Cross提出。该法 于1932年首次公布时便立刻受到了注意,并被承认是20世纪结构分析中最显著的进步之一。 弯矩分配法是一种逐次近似计算法,可以实现任何需要的精度。本质上来说,该法首先假定 结构的每一个节点是固定的。然后连续地解开和锁住每个节点,节点的内部弯矩被分配和平 衡,直到节点转至它们最终的或几乎最终的位置。 It will be found that this process of calculation is both repetitive(重复的)and easy to apply. Before explaining the techniques of moment distribution, however, certain definitions and concepts must be presented(介绍). Clockwise moments that act on the member are considered positive, whereas counterclockwise(反时针的)moments are negative. The moments at the “walls”(墙壁)or fixed joints of a loaded member are called fixed-end moments(固端弯矩). The member stiffness factor at A can be defined as the amount of moment M required to rotate the -connected to a joint, then by the principle of superposition, the total stiffness factor at the joint is the sum of the member stiffness 发现该计算过程是重复的且容易运用。但是在解释弯矩分配法的技术之前,必须介绍某些定 义和概念。作用在构件上的顺时针弯矩为正,而逆时针弯矩为负。“墙”上的弯矩或负荷构 件上固定节点的弯矩称为固端弯矩。构件在A点的刚度系数可定义为使梁端A转动值 弧度所需要的弯矩M的值。如果一些构件与一个节点固接,则根据叠加原理,该节点处总 的刚度系数为该节点处的构件刚度系数的总和,即。 This value represents the amount of moment needed to rotate the joint through an angle of 1 rad. If a moment M is applied to a fixed-connected joint, the connecting members will each supply a portion of(一部分)the resisting moment necessary to satisfy moment equilibrium at the joint. That fraction of(部分) the total resisting moment supplied by the member is called the distribution factor (DF)(分配系数). The carry-over factor(传递系数)represents the fraction of M that is “carried over” from the pin to the far end. 这个值代表了使该节点转动1弧度的角度所需要的弯矩数量。如果将弯矩M施加于 固定连接节点,则相连的构件各自提供一部分满足节点弯矩平衡必需的抵抗弯矩。在总的抵 抗弯矩中由单个构件提供的部分称为分配系数(DF)。传递系数代表着弯矩从铰传递至远端 的部分。 作业练习 通过两篇Reading Materials的学习,进一步了解力法应用的一般程序和较复杂结构框架的矩 阵法分析过程(即为计算结构力学)。 Unit 7 第七单元 Reinforced Concrete Structures 钢筋混凝土结构 教学目标 了解钢筋混凝土的力学性能 了解采用混凝土结构的优缺点 了解国外建筑规范的发展历史 熟悉钢筋混凝土结构中的专业词汇 熟悉科技类文献的常用句型 熟悉institute、association、society的用法;regulation、specification、code的用法;result in、 give rise to、lead to的用法;reinforcing bar、reinforcing steel、steel bar、reinforcement的含 义;involve、include、cover的用法;due to、stem from、because of的用法;construction、 function、compressive、allow、form的不同含义。 Concrete and reinforced concrete are used as building materials in every country. In many, including the United States and Canada, reinforced concrete is a dominant(主要的) structural material in engineered construction(建造的建筑物). The universal(通用的)nature of reinforced concrete construction stems from(归因于)the wide availability of reinforcing bars(钢筋)and the constituents(组成部分)of concrete, gravel,sand, and cement, the relatively simple skills required in concrete construction(施工), and the economy(经济性)of reinforced concrete compared to other form of construction. Concrete and reinforced concrete are used in bridges, buildings of all sorts(各种各样), underground structures, water tanks, television towers, offshore oil exploration and production structures(近海石油开采和生产结构), dams, and even in ships. 混凝土与钢筋混凝土作为建筑材料在每个国家被使用着。在很多国家,包括美国和加拿大, 钢筋混凝土是建造的建筑物中主要的结构材料。钢筋混凝土建筑物通用的特性归因于能大量 得到钢筋和混凝土的组分(即碎石、砂和水泥),混凝土施工需要相对简单的技术,以及与 其他形式的建筑相比钢筋混凝土的经济性。混凝土与钢筋混凝土用于桥梁、各种房屋、地下 结构、水箱、电视塔、近海石油开采和生产结构、大坝甚至船舶。 Mechanics of Reinforced Concrete 钢筋混凝土的力学 Concrete is strong in compression but weak in tension. As a result, cracks develop(形成) whenever(每当)loads, or restrained shrinkage(收缩限制)or temperature changes, give rise to (导致)tensile stresses in excess of(超过)the tensile strength of the concrete. In the plain concrete(素混凝土)beam, the moments due to applied loads are resisted by an internal tension-compression couple(拉压力偶)involving tension in the concrete. Such a beam fails very suddenly and completely when the first crack forms. In a reinforced concrete beam, steel bars(钢 筋)are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be developed in the bars. 混凝土受压强、受拉弱。因此,每当受荷、收缩受阻或温度变化引起的拉应力超过混凝土的 抗拉强度时,便会发生开裂。在素混凝土梁中,因外力引起的力矩由内部的拉-压形成的力 偶来抵抗,此力偶中包含了混凝土的拉力。当第一条裂缝形成时,此梁会突然、完全地失效。 在钢筋混凝土梁中,钢筋埋置在混凝土内的方式应能使混凝土开裂后在钢筋中产生平衡力矩 所需的拉力。 The construction(施工)of a reinforced concrete member involves building a form or mold(模 具)in the shape of the member being built. The form must be strong enough to support the weight and hydrostatic pressure(静水压力)of the wet concrete, and any forces applied to it by workers, concrete buggies(料车), wind, and so on. The reinforcement(钢筋)is placed in this form and held in place(固定就位)during the concreting(用混凝土浇筑)operation. After the concrete has hardened, the forms are removed(拆除). 钢筋混凝土构件的施工包括以在建构件的形状搭建模板或模具。模板必须足够 强劲以支承湿混凝土的重量和静水压力,以及任何由工人、混凝土料车、风等施加给它的力。 钢筋置于模板中,并在混凝土浇筑过程中固定就位。当混凝土硬化后便拆除模板。 The choice of whether a structure should be built of concrete, steel, masonry, or timber(木材) depends on the availability(可得性)of materials and on a number of(许多)value decisions(价 值判断). 一个结构选择由混凝土、钢材、砌体还是木材建造取决于材料的可得性和许多 价值判断。 Factors Affecting Choice of Concrete For a Structure 影响一个结构选择混凝土的因素 Economy Frequently, the foremost(最重要的)consideration is the overall cost(总费用) of the structure. This is, of course, a function of the costs(费用函数)of the materials and the labor necessary to erect them. Frequently, however, the overall cost is affected as much or more by the overall construction time(总的建造时间)since the contractor and owner must allocate(分配) money(资金)to carry out the construction and will not receive a return on this investment (收 回投资)until the building is ready for occupancy(居住). As a result, financial savings(财务 的节约)due to rapid construction may more than offset(足以抵消)increased material costs. Any measures designer can take to standardize the design and forming(加工)will generally pay off(使人得益)in reduced overall costs. 经济性 最重要的考虑常常是该结构的总费用。当然,这是一个建造结构而必需的材料 和劳动力费用的函数。但是,总费用经常同样地或更多地受总的建造时间的影响,因为承包 商和业主必须分配资金来进行建造,并直到建筑物可以使用才能收回投资。因快速施工而使 财务的节约可足以抵消增加的材料费用。设计者为使设计和加工标准化所采取的任何措施通 常都将在降低的总费用中得益。 In many cases the long-term economy(长期的经济性)of the structure may be more important than the first cost. As a result, maintenance(维护)and durability(耐久性)are important considerations. 在很多情况下,结构长期的经济性可能比初始费用更重要。因此,维护和耐久 性是重要的考虑因素。 Suitability of Material for Architectural and Structural Function A reinforced concrete system frequently allows the designer to combine the architectural and structural functions(功能). Concrete has the advantage that it is placed in a plastic condition(塑性状态) and is given the desired shape and texture(密度)by means of the forms and the finishing techniques(加工技术). This allows such elements(构件)as flat plates or other types of slabs to serve as load-bearing elements while providing the finished floor and ceiling surface(楼面和顶棚 面). Similarly, reinforced concrete walls can provide architecturally attractive surfaces in addition to having the ability to resist gravity, wind, or seismic loads. Finally, the choice of size or shape is governed(决定)by the designer and not by the availability of standard manufactured members. 材料对建筑和结构功能的适应性 钢筋混凝土系统常常允许设计者将建筑和结构的功能结 合起来。混凝土的优势是能以塑性的状态放置,并通过模板和加工技术给出需要的形状和密 度。当楼面和顶棚面完成时,允许这些构件诸如平面板或其他类型的板充当受力构件。类似 地,钢筋混凝土墙除了能抵抗重力、风或地震荷载外,还能提供建筑上吸引人的外观。最后, 尺寸和形状的选择由设计者来决定,而不是由标准制造构件的可得性来决定。 Fire Resistance The structure in a building must withstand the effects of a fire and remain standing(直立)while the building is evacuated(撤空)and the fire is extinguished(熄灭). A concrete building inherently(固有地)has a 1- to 3-hour fire rating(耐火等级)without special fireproofing (防火)or other details(说明). Structural steel or timber(钢结构或木结构) buildings must be fireproofed to attain similar fire ratings. 抗火性 当房屋被撤空、火被熄灭时,建筑中的结构必须经得起火的影响,并仍能保持 直立。混凝土房屋在没有采取特殊的防火措施或其他说明的情况下本来就有1-3小时的耐火 等级。钢结构或木结构的房屋必须采取防火措施,以得到相似的耐火等级。 Rigidity The occupants of a building may be disturbed (干扰)if their building oscillates (摇动)in the wind or the floors vibrate as people walk by(走过). Due to the greater stiffness and mass(刚度和质量)of a concrete structure, vibrations are seldom a problem. 刚性 如果房屋在风中摇动,或者人们走过时底板振动,则房屋的居住者可能会被干 扰。由于混凝土结构具有较大的刚度和质量,振动很少成为问题。 Low Maintenance Concrete members inherently require less maintenance than do structural steel or timber members (结构钢构件或结构木构件). This is particularly true(尤其正确)if dense, air-entrained concrete has been used for surfaces exposed to the atmosphere, and if care has been taken in the design to provide adequate drainage off and away (使水排出) from the structure. 低维护性 混凝土构件比结构钢构件或结构木构件需要的维护本来就少。特别是当暴 露在空气中的表面混凝土采用密实的加气混凝土,并在设计中小心地让水分充分地排出结构 时更是如此。 Availability of Materials Sand, gravel, cement, and concrete mixing facilities(搅拌设施) are very widely available, and reinforcing steel(钢筋)can be transported to most job sites(施工 现场)more easily than can structural steel(结构钢). As a result, reinforced concrete is frequently used in remote areas. 材料的可得性 砂、碎石(砾石)、水泥以及混凝土的搅拌设施可以非常广泛的得到, 且钢筋比结构钢更容易地运至多数施工现场。因此,钢筋混凝土经常用在偏远的区域。 On the other hand, there are a number of factors that may cause one to select a material other than (..除外,不是..)reinforced concrete. These include: 另一方面,有许多因素可能导致一个人选择的材料不是钢筋混凝土。这包括: Low Tensile Strength As stated(叙述)earlier, the tensile strength of concrete is much lower than its compressive strength (about 1/10), and hence concrete is subject to(易遭受)cracking. In structural uses this is overcome by using reinforcement to carry tensile forces and limit crack widths(宽度)to within acceptable values. Unless care is taken in design and construction, however, these cracks may be unsightly(难看)or may allow(使..能)penetration(渗透)of water. 低的抗拉强度 正如前面所述的,混凝土的抗拉强度比它的抗压强度要低得多(约 1/10),因而混凝土易遭受开裂。在结构使用中,通过采用钢筋承受拉力,并限制裂缝宽度 在可接受的数值内来克服这一点。但是,除非在设计与施工中小心谨慎,否则这些裂缝可能 会难看或使水渗透。 Forms and Shoring The construction of a cast-in-place structure(现浇结构) involves(涉及)three steps(步骤)not encountered in the construction of steel or timber structures. These are (a) the construction of the forms, (b) the removal(拆除)of these forms, and (c) propping or shoring(支撑)the new concrete to support its weight until its strength is adequate. Each of these steps involves(包含)labor(人工)and/or materials which are not necessary with other forms of construction(建筑形式). 模板和支撑 现浇结构的施工涉及到三个步骤在钢结构或木结构的施工中不会遇到。 它们是(a)模板的施工;(b)模板的拆除;(c)支撑新浇混凝土,支撑其重量直至混凝土达到足 够的强度。每一步都包括其他建筑形式中不必要的人工和/或材料。 Relatively Low Strength Per Unit of Weight or Volume The compressive strength of concrete is roughly 5% to 10% that of steel, while its unit density is roughly 30% that of steel. As a result, a concrete structure requires a larger volume and a greater weight of material than does a comparable(类似的) steel structure. As a result, long-span structures(大跨结构)are often built from steel. 相对低的单位重量或单位体积的强度 混凝土的抗压强度大约是钢材的5%-10%, 而它的单位密度约是钢材的30%。因此,混凝土结构与类似的钢结构相比需要较大的材料 体积和较重的材料重量。因此,大跨结构常常由钢材制造。 Time-dependent volume changes Both concrete and steel undergo approximately the same amount of thermal expansion and contraction. Because there is less mass of steel to be heated or cooled(变热或变冷), and because steel is a better conductor(导体)than concrete, a steel structure is generally affected by temperature changes to a greater extent (程度)than is a concrete structure. On the other hand, concrete undergoes drying shrinkage(干缩), which, if restrained, may cause deflections or cracking. Furthermore, deflections will tend to increase with time(随时间), possibly doubling(双倍), due to creep(徐变)of the concrete under sustained loads(持续荷载). 体积随时间变化 混凝土与钢筋都经过了大约相同量的热膨胀和收缩。因为变热或变冷的 钢材质量较少,且钢材与混凝土相比是一种较好的导体,因此,钢结构通常受温度变化的影 响程度比混凝土结构要大。另一方面,混凝土经历了干缩,如果受到约束,干缩可能会引起 挠度或开裂。而且,挠度往往会随着时间增加,其值由于混凝土在持续荷载作用下的徐变而 可能会是两倍。 The first set of building regulations(建筑规范)for reinforced concrete were drafted(起草)under the leadership of(在..的领导下) Professor Morsch of the University of Stuttgart and were issued(发布)in Prussia in 1904. Design regulations were issued in Britain, France, Austria, and Switzerland between 1907and 1909. 在Stuttgart(斯图加特)大学Morsch教授的领导下起草了第一套钢筋混凝土 的建筑规范,并于1904年在Prussia(普鲁士)发布。1907-1909年在英国、法国、奥地利 和瑞士发布了设计规范。 Building Codes 建筑规范 The American Railway Engineering Association(协会) appointed(任命)a Committee on Masonry(砌体委员会)in 1890. In 1903 this committee presented(提出)specifications for Portland cement concrete. Between 1908 and 1910 a series of committee reports led to the Standard Building Regulations for the Use of Reinforced Concrete published(发表)in 1910 by the National(国家的)Association of Cement Users(用户)which subsequently(随后)became the American Concrete Institute(协会). 美国的铁路工程协会在1890年任命了一个砌体委员会。该委员会在1903年提 出了波特兰水泥混凝土的规范。1908-1910间,一些列的委员会报告使国家水泥用户协会在 1910年发表了钢筋混凝土使用的标准建筑规范,其随后成为美国混凝土协会。 A Joint Committee(联合委员会)on Concrete and Reinforced Concrete was established in 1904 by the American Society of Civil Engineers(土木工程师协会), American Society for Testing and Materials, the American Railway Engineering Association, and the Association of American Portland Cement Manufactures. This group was later joined by(加入)the American Concrete Institute. Between 1904 and 1910 the Joint Committee carried out research. A preliminary (初步 的)report issued in 1913 lists the more important papers and books on reinforced concrete published(发表)between 1898 and 1911. The final report of this committee was published in 1916. The history of reinforced concrete building codes in the United States was reviewed(回顾) in 1954 by Kerekes and Reid. 水泥与钢筋混凝土的联合委员会于1904年建立,包括美国土木工程师协会、美国测试和材 料协会、美国铁路工程协会和美国波特兰水泥制造协会。该团体中后来又加入了美国混凝土 协会。在1904-1910年间,联合委员会进行了研究。在1913年发布的初步报告中列出了在 1898-1911年间发表的关于钢筋混凝土的较重要的文件和书籍。该委员会最后的报告发表于 1916。Kerekes and Reid在1954对钢筋混凝土建筑规范在美国的发展历史作了回顾。 The design and construction of buildings is regulated(控制)by municipal bylaws(市政细则) called building codes. These exist to protect(用以保护)the public health and safety. Each city and town is free to(允许)write(编制)or adopt its own building code, and in that city or town, only that particular code has legal status(合法地位). Because of the complexity of building code writing, cities in the United States generally base their building codes on one of three model(典 型)codes: the Uniform(统一)Building Code, the Standard Building Code, or the Basic Building Code. These codes cover(包括) such things as use and occupancy requirements, fire requirements, heating and ventilating(供热和通风) requirements, and structural design. 建筑的设计和施工是由称为建筑规范的市政细则来控制的。这些规范是用以保护公众的健康 和安全。每个城市和城镇允许编制或采用其自己的建筑规范,并且在那个城市或城镇只有那 个特定的规范才有合法的地位。由于建筑规范编制的复杂性,美国的城市通常将它们的建筑 规范以三个典型规范中的一个为基础,即统一建筑规范、标准建筑规范或基本建筑规范。这 些规范包括诸如使用和居住的要求,防火要求、供热和通风要求以及结构的设计。 The definitive(最终的)design specification for reinforced concrete buildings in North America(北美)is the Building Code Requirements for Reinforced Concrete (ACI-318-95), which is explained in a Commentary(说明). 在北美,钢筋混凝土建筑最终的设计规范是钢筋混凝土建筑规范要求 (ACI-318-95),并通过说明(对该规范要求)加以解释。 This code, generally referred to as (指..) the ACI Code, has been incorporated(体现)in most building codes in the United States and serves as the basis for comparable codes in Canada, New Zealand, Australia, and parts of Latin America. The ACI Code has legal status only if(只要) adopted in a local(当地的)building code. 该规范通常称为ACI规范,它已经在美国的大多数建筑规范中被体现,并作 为加拿大、新西兰、澳大利亚和部分拉丁美洲国家类似规范的基础。ACI规范只要在当地的 建筑规范中被使用便拥有合法的地位。 The rules for the design of concrete highway bridges(公路桥) are specified in the Standard Specifications for Highway Bridges, American Association of State Highway and Transportation Officials(美国国家公路和运输官方协会), Washington, D.C.(哥伦比亚华盛顿特区). 混凝土公路桥的设计规则在哥伦比亚华盛顿特区的美国国家公路和运输官方 协会对公路桥的标准规范中作了规定。 Each nation or group of(一群)nations in Europe has its own building code for reinforced concrete. The CEB-FIP Model Code for Concrete Structures is intended to(用来)serve as the basis for future attempts to unify(统一)European codes. This code and the ACI Code are similar in many ways. 在欧洲每个国家或一群国家都有自己的钢筋混凝土建筑规范。混凝土结构的 典型规范CEB-FIP被用来作为将来尝试统一欧洲规范的基础。该规范在很多方面与ACI规 范是相似的。 作业练习 通过一篇Reading Material的学习,进一步了解混凝土作为结构材料的历史发展情况。 Unit 8 第八单元 Columns: Combined Axial Load and Bending 柱:轴向力与弯曲的组合 教学目标 了解柱子中箍筋的布置特点 了解相关图的确定和使用 了解短柱设计中的注意问题 熟悉钢筋混凝土柱子中的专业词汇 熟悉科技类文献中的常用句型 熟悉tie、spiral、stirrup的区别;limit、restrain、confine、hold的用法;refer to、be referred to、 be referred to as 的区别;a family of、a series of、 a portion of 、great majority of的区别。 A column is a vertical structural member transmitting axial compressive loads(压缩荷载), with or without moments. The cross-sectional dimensions of a column are generally considerably less than(远小于)its height. Columns support vertical loads from the floors and roof and transmit these loads to the foundations. 柱是竖向的结构构件,传递轴向压缩荷载和弯矩(或无弯矩)。柱的横截面尺 寸通常远远小于其高度。柱子支承着来自楼面和屋面的竖向荷载,并将它们传于地基。 In construction, the reinforcement and concrete for the beams and slabs in a floor are placed. Once this concrete has hardened, the reinforcement and concrete for the columns over that floor are placed, followed(接着)by the next-higher floor(下一个更高楼面). 施工时,将楼面梁和楼面板的钢筋与混凝土放入。一旦混凝土已经变硬,则将 该层柱子的钢筋和混凝土放入,紧接着进行下一个更高楼面的(施工)。 The more general terms(通用的术语)compression members or members subjected to combined axial load and bending are sometimes used to refer to(指、表示)columns, walls, and members in concrete trusses or frames. These may be vertical(垂直的), inclined(倾斜的), or horizontal (水平的). A column is a special case(特殊的例子)of a compression member that is vertical. 有时采用较通用的术语即受压构件或承受轴向力和弯曲组合的构件来表示柱 子、墙和混凝土桁架或框架中的构件。这些构件可以是垂直的、倾斜的或水平的。柱子是受 压构件中一种特殊的例子,即垂直的。 Stability effects(影响)must be considered in the design of compression members. If the moments induced(引起)by slenderness effects(细长度效应)weaken a column appreciably(明显地), it is referred to as a slender column or a long column. The great majority of(绝大多数的)concrete columns are sufficiently stocky(非常粗短的)that slenderness can be ignored. Such columns are referred to as short columns. 在设计受压构件时必须考虑稳定性的影响。如果由于细长度效应引起的弯矩明 显地削弱了柱子,它被称为细长柱或长柱。绝大多数的混凝土柱子是非常粗短的,以致可以 忽略其细长度。这样的柱子称为短柱。 Tied and Spiral Columns 普通箍筋和螺旋箍筋的柱子 Over(超过)95% of all columns in buildings in nonseismic regions(非地震区)are tied columns. Tied columns may be square(正方形), rectangular, L shaped, circular, or any other required shape. Occasionally when high strength and/or high ductility(延性)are required, the bars are placed in a circle(圆环)and the ties are replaced by a bar bent into a helix or spiral(螺旋线), with a pitch (间距)of 1.375 to 3.375 in.(英寸). Such a column is called a spiral column. Spiral columns are generally circular, although square or polygonal(多边形)shapes are sometimes used. The spiral acts to restrain the lateral expansion(横向扩张)of the column core under axial loads causing crushing(压碎), and in doing so, delays(延缓)the failure of the core, making the column more ductile. 在非地震区域的建筑物中超过95%的柱子是普通箍筋的柱子。普通箍筋的柱子可以是正方 形、矩形、L形、圆形或其它任何需要的形状。偶尔当需要高强度和/或高延性时,将钢筋 置入一个圆环,普通箍筋由弯成螺旋线的钢筋代替,间距为1.375-3.375英寸。该柱子称为 螺旋箍筋柱。螺旋箍筋柱通常是圆形的,尽管有时也用正方形或多边形。螺旋箍筋的作用是 约束柱子的核心在导致压碎的轴向荷载作用下的横向扩张,并据此延缓其核心的破坏,使柱 子具有更好的延性。 In seismic regions the ties are heavier(较粗)and much more closely spaced(密集). Spiral columns are used more extensively in such region. In a spiral column, the lateral expansion of the concrete inside the spiral (referred to as the core) is restrained by the spiral. 在地震区箍筋较粗且密集得多。螺旋箍筋柱较广泛地用于这样的地区(即地震 区)。在螺旋箍筋柱中,螺旋箍筋内部的混凝土(称为核心)的横向扩张受到螺旋箍筋的约 束。 In a tied column in a nonseismic region, the ties are spaced roughly(约)the width of the column apart(间隔为), and as a result, provide relatively little lateral restraint to the core. Outward(向 外的)pressure on the sides of the ties due to lateral expansion of the core merely(仅仅)bends them outward, developing a negligible(可忽略的) hoop stress effect(环向应力效应). Hence normal(普通)ties have little effect on the strength of the core in a tied column. They do, however, act to reduce the unsupported length of the longitudinal bars, thus reducing the danger of buckling (屈曲)of those bars as the bar stress approaches yield. 在非地震区的普通箍筋柱中,普通箍筋相隔的间距约为柱子的宽度,因此对核心混凝土提供 了比较小的横向约束。由于核心(混凝土)的横向扩张导致普通箍筋边上向外的压力仅使普 通箍筋向外弯曲,形成一个可忽略的环向应力效应。因此,在普通箍筋柱中,普通的箍筋对 核心混凝土的强度几乎没什么影响。但是它们减少了纵向钢筋未被支撑的长度,这样当钢筋 的应力接近屈服时可减少这些钢筋发生屈曲的危险。 When the shell(外壳)spalls off(剥落)the spiral column, the column does not fail immediately because the strength of the core has been enhanced(加强)by the triaxial stresses resulting from the effect of the spiral reinforcement(加强). As a result, the column can undergo large deformations, eventually reaching a second(另一个)maximum load when the spirals yield and the column finally collapses. Such a failure is much more ductile and gives warning of the impending (即将发生的) failure together with possible load redistribution(重分布)to other members. It should be noted, however, that this is accomplished(实现)only at very high strains. For example, the strains necessary to reach the second(第二个)maximum load correspond to a shortening of about 1 in. in an 8-ft-high column. When spiral columns are eccentrically(偏心)loaded, the second maximum load may be less than the initial maximum, but the deformations at failure are still large, allowing load redistribution. 当外壳(混凝土)从螺旋箍筋柱上剥落时,柱子并没有立即失效,因为核心(混凝土)的强 度由于螺旋箍筋的加强效应形成的三向应力而增强。因此,当螺旋箍筋屈服时柱子能经受大 变形,最后达到另一个最大荷载,并最终倒塌。这样的失效更延性,并对即将发生的失效和 可能的对其它构件的荷载重分布给予警告。但是应该注意到,这只有在非常大的应变时才能 实现。例如,要达到第二个最大荷载,其应变必须相当于8英尺高的柱子缩短约1英寸。当 螺旋箍筋柱受到偏心荷载时,第二个最大荷载可能小于初始的最大荷载,但失效时的变形仍 然是大的,允许荷载重分布。 When a symmetrical(对称的)column is subjected to a concentric(中心) axial load, longitudinal strains develop uniformly across(穿过)the section. Because the steel and concrete are bonded together, the strains in the concrete and steel are equal. For any given strains it is possible to compute the stresses in the concrete and steel using the stress-strain curves(应力-应变曲线)for the two materials. 当一根对称的柱子承受中心轴向力时,则穿过截面均匀地形成纵向应变。由于 钢筋与混凝土粘结在一起,混凝土的应变与钢筋的应变是相等的。对任何已知的应变,通过 采用(混凝土与钢筋)两种材料的应力-应变曲线有可能计算出混凝土与钢筋的应力。 Interaction Diagrams 相关图 Almost all compression members in concrete structure are subjected to moments in addition to axial loads. These may be due to the load not being centered(居中)on the column, or may result from the columns resisting a portion of the unbalanced moments at the ends of the beams supported by the columns. The distance e is referred to as the eccentricity(偏心距)of the load. These two cases are the same since the eccentricity load P can be replaced by a load P acting along the centroidal axis(形心轴), plus a moment, M=Pe, about the centroid. The load P and moment M are calculated with respect to the geometric centroidal axis because the moments and forces obtained from structural analysis are referred to(关系到)this axis. 在混凝土结构中,几乎所有的受压构件除了承受轴向力外,还承受弯矩。这可能是由于柱子 上的荷载没有居中,或者可能是由柱子抵抗其支撑的梁端的部分不平衡弯矩而引起。距离e 称为荷载的偏心距。因为有偏心距的荷载P可以替换成沿着形心轴作用的荷载P加上对形 心的弯矩,即M等于Pe,因此这两种情况是相同的。荷载P和弯矩M是相对于几何形心 轴来计算的,因为从结构分析得到的弯矩和力关系到该轴。 Although it is possible to derive a family of(一族)equations to evaluate the strength of columns subjected to combined bending and axial loads, these equations are tedious(冗长)to use. For this reason, interaction diagrams for columns are generally computed by assuming a series of strain distributions, each corresponding to a particular point on the interaction diagram, and computing the corresponding values (对应值)of P and M. Once enough such points have been computed, the results are summarized(概括)in an interaction diagram. 尽管有可能推导一族公式来估计承受弯曲与轴向力组合的柱子的强度,但是这 些公式用起来很冗长。因此,柱子的相关图通常通过假定一系列的应变分布来计算,每一个 (应变)相当于相关图上一个特定的点,并计算出对应的P和M的值。一旦这样的点已经 计算得足够(多),其结果则被概括在一张相关图中。 The maximum compressive strain(压应变)is set(设定)at 0.003, corresponding to failure of the section. The location of the neutral axis(中性轴)and the strain in each level of reinforcement(每 层的钢筋)are computed from the strain distribution. This information is then used to compute the size of the compression stress block(区)and the stress in each layer of reinforcement. The forces in the concrete and the steel layers are computed by multiplying the stresses by the areas on which they act. Finally, the axial force Pn is computed by summing(求和)the individual(各个)forces in the concrete and steel, and the moment Mn is computed by summing the moments of these forces about the geometric centroid of the cross section. These values of Pn and Mn represent one point on the interaction diagram. 最大的压应变设定在0.003,相当于该截面的失效。中性轴的位置和每层钢筋的应变通过应 变的分布来计算。这个信息然后用以计算压应力区的大小和每层钢筋的应力。混凝土与钢筋 层中的力通过应力乘以其作用的面积来计算。最后,轴向力Pn通过混凝土与钢筋中的各个 力的求和得到,弯矩Mn通过这些力对横截面的几何形心的弯矩求和得到。这些Pn和Mn 的值代表着相关图上的某一点。 Generally, designers have access to(利用)published interaction diagrams or computer programs (程序)to compute interaction diagrams for use in design. Occasionally, this is not true, as for example, in the design of hollow bridge piers(墩), elevator shafts, or unusual shaped members. In most cases it is adequate to represent(表示)the interaction diagram by a series of straight lines joining(加上)the load and moment values corresponding to the following(下列)five strain distributions: 通常设计者可以利用已经发表的相关图或利用计算机程序来计算用于设计的 相关图。有时候这不太正确,例如在设计空心桥墩、电梯井或特殊形状的构件时。在多数情 况下,一系列的直线加上相应于下列五种应变分布的力和弯矩值可足以表示出相关图: A uniform compressive strain of 0.003. A strain diagram corresponding to incipient(初始的) cracking, passing through(经过)a compressive strain of 0.003 on one face and zero strain on the other. The balanced strain distribution having a compressive strain of 0.003 on one face and a tensile strain of - 1. 一个为0.003的平均压应变; 2. 相应于初始开裂的应变图,在一个端面上的压应变为0.003,而在另一个端面上为零应 变; 3. 一个平衡的应变分布,在一个端面上的压应变为0.003,而在靠近另一个端面的钢筋中 的拉应变为-( 等于屈服应变); A tension failure case with 0.003 compressive strain on one face and -on the other face. A uniform tensile strain of - concrete cracked. 一个受拉失效的情况,即一个端面上的压应变为0.003,另一个端面的钢筋中的拉应变为 -; 钢筋中一个平均的拉应变为-,而混凝土开裂。 It is difficult to calculate the pure moment(纯弯矩)case directly. If this value is required for a symmetrical section, it can be estimated as the larger of (1) the flexural capacity(抗弯能力) ignoring the reinforcement in the compressive zone, or (2) the moment computed ignoring the 很难直接计算纯弯矩的情况。如果一个对称的截面需要该值,可以估计为(下 列两个值中的)较大者:(1)忽略了受压区钢筋的抗弯能力;(2)忽略了混凝土、并假定临 近每一个端面的钢筋中的应变为时计算的弯矩。 Design of Short Columns If the cross section is known and it is necessary to compute the capacity, an analysis is carried out. On the other hand, if the loads and moments are known and it is necessary to select a cross section to resist them, the procedure is referred to as design or proportioning(确定尺寸). A design problem is solved by guessing(假定)a section, analyzing whether it will be satisfactory, revising(修正)the section, and reanalyzing it. In each case the analysis portion of the problem is most easily carried out using interaction diagrams. 短柱的设计 如果已知横截面,且必须计算其能力,则可进行分析。另一方面,如果已知荷载和弯矩,且 必须选择一个横截面来抵抗它们,这个过程称为设计或确定尺寸。设计问题是通过假定一个 截面,分析它是否满足要求,修正该截面,然后再重新分析它来解决的。在每个情况下,问 题的分析部分采用相关图是最容易进行的。 ACI Code requires a clear(净)concrete cover(保护层)of not less than 1.5 in. to the ties or spirals in columns. More cover may be required for fire protection(防火)in some cases. The concrete for a column is placed in the core inside the bars and must be able to flow out(流动)between the bars and the form. To facilitate(促进)this, the ACI code requires that the minimum clear distance between longitudinal bars shall not be less than the larger of 1.5 times the longitudinal bar diameter, 1.5 in. or 1.333 times the size of the coarse aggregate(粗骨料). These clear distance limitation also apply to the clear distance between lap spliced(搭接)bars and adjacent bars or lap splices. Because the maximum number of bars occurs at the splices(拼接), the spacing of bars at this location generally governs. ACI规范要求混凝土的保护层至柱子中的普通箍筋或螺旋箍筋的净距不少于1.5英寸。在某 些情况下,为了防火,可能需要更多的保护层。柱子的混凝土灌入钢筋之间的核心区,且必 须能在钢筋和模板之间流动。为了促进流动,ACI规范要求纵向钢筋之间的最小净距离不少 于1.5倍的纵向钢筋直径、1.5英寸或1.333倍的粗骨料尺寸中的较大值。这些净距的限制也 适用于搭接钢筋与相邻钢筋之间或搭接钢筋之间的净距(要求)。由于最多的钢筋数量发生 在拼接处,因此钢筋在该处的间距通常起到控制作用。 In most buildings in nonseismic zones, the longitudinal bars in the columns are spliced just above each floor. The requirements for lap splices vary(变化)depending on the state of stress in the bar at ultimate load(极限荷载). Generally, all the bars in a column will have the same length or splice regardless of whether they are on the tension or compression face. This is done to reduce the chance(可能性)of field(现场)errors. 在非地震区的多数建筑中,柱子中的纵向钢筋刚好在每层楼面的上方拼接。搭 接的要求随钢筋在极限荷载下的应力状态而变化。通常,柱子中的所有钢筋具有相同的长度 或接头,不管它们是处于受拉面还是受压面。这样做是为了减少现场错误的可能性。 (1)restrain the longitudinal bars from buckling out through the surface of the column. ACI Code gives limits on the size, spacing, and the arrangement(布置)of the ties so that they are adequate to restrain the bars. The minimum tie size is a No.3 bar for longitudinal bars up to (在..以内)No.10, and a No.4 bar for larger longitudinal bars, or for bundled bars(束 筋). The vertical spacing of ties shall not exceed 16 longitudinal bar diameters to limit the unsupported length of these bars, and shall not exceed 48 tie diameters to ensure that the cross-sectional area of the ties is adequate to develop the forces needed to restrain buckling of the longitudinal bars. The maximum spacing is also limited to the least dimension of the column. In seismic regions much closer spacings are required. Ties are provided in reinforced concrete columns for four reasons: 钢筋混凝土柱子中采用箍筋有四个原因: (1)箍筋阻止了纵向钢筋向柱子表面的屈曲。 ACI规范给出了对箍筋尺寸、间距和布置的限制,以使它们足以约束钢筋。 对10号以内的纵筋其最小箍筋的尺寸是3号,对较大的纵筋或束筋其(最小箍筋的尺寸) 为4号。箍筋的竖向间距不超过16倍的纵筋直径以限制这些纵筋未被支撑的长度,且不超 过48倍的箍筋直径以确保箍筋的横截面面积足以形成为约束纵向筋屈曲所需要的力。(箍 筋)最大的间距也被限制为柱子的最小尺寸。在地震区需要的间距要密得多。 (2)Ties hold(固定)the reinforcement cage(笼)together during the construction process. (3)Properly detailed(布置)ties confine(约束)the concrete core, providing increased ductility. (2)在施工过程中箍筋将钢筋笼固定在一起。 (3)适当布置的箍筋约束着核心混凝土,以增加延性。 (4)Ties serve as shear reinforcement(抗剪钢筋)for columns. If shear governs, the smaller spacing (d/2, d = effective depth) must be used and the area of all legs(箍筋肢)parallel to the direction of the shear force must satisfy ACI Code. ACI Code requires that bar anchorage(锚固钢筋)in connections of beams and columns be enclosed(包围)by ties, spirals, or stirrups(钢筋箍). (4)箍筋作为柱子的抗剪钢筋。 如果由剪力控制,则必须采用较小的间距(即1/2d,d为有效深度),且所有 平行于剪力方向的(箍筋)肢的面积必须满足ACI规范。ACI规范要求连接梁与柱的锚固 钢筋应被普通箍筋、螺旋箍筋或钢筋箍包围。 Finally, extra ties are required at the outside(外部)(lower) end of offset bends(迂回管弯头) at column splices to resist the horizontal force component in the sloping(倾斜)portion of the bar. 最后,在柱子拼接处的迂回管弯头的外部较低端需要额外的箍筋,以抵抗钢筋 倾斜部分的水平力分量。 作业练习 通过一篇Reading Material的学习,进一步了解钢筋混凝土柱子在框架结构中的设计、分析 特点和有关要求。 Unit 9 第九单元 Cracking Load and Ultimate Moment 开裂荷载和极限弯矩 教学目标 了解预应力梁在开裂荷载下的反应 了解有(无)粘结力的预应力构件的极限弯矩能力 熟悉预应力构件中的专业词汇 熟悉科技类文献中的常用句型 熟悉criterion (criteria)、modulus (moduli)、index (indices)的单复数区别;offset、counteract、 against的含义;significant、yield的不同含义;conform to、compliance with的含义;be subject to、be subjected to的不同含义;predict、anticipate的用法;lightly、slightly、highly的不同 含义。 It has been shown that a variation in the external load acting on a prestressed beam results in a change in the location of the pressure line(压力线)for beams in the elastic range. This is a fundamental principle(规律)of prestressed construction. In a normal prestressed beam, this shift (移动)in the location of the pressure line continues at a relatively uniform rate(速度), as(随 着)the external load is increased, to the point where cracks develop in the tension fiber. After the cracking load has been exceeded, the rate of movement in the pressure line decreases as additional load is applied, and a significant(显著)increase in the stress in the prestressing tendon(预应力 钢筋束)and the resultant concrete force begins to take place. Action Under Overload-Cracking Load 超载(-开裂荷载)下的反应 This change in the action of the internal moment continues until all movement of the pressure line ceases(停止). The moment caused by loads that are applied thereafter(其后)is offset(抵消) entirely by a corresponding and proportional change in the internal forces, just as in reinforced-concrete construction. This fact, that the load in the elastic range and the plastic range is carried by actions that are fundamentally different, is very significant(重要的) and renders (使..变得)strength computations essential for all designs in order to ensure that adequate safety factors exist. This is true even though the stresses in the elastic range may conform to(符合)a recognized(公认的)elastic design criterion. 已经显示作用在一根预应力梁上的外部荷载的变化会导致梁在弹性阶段时其压力线位置的 变化。这是预应力结构的基本规律。在一根普通的预应力梁中,随着外力的增加,其压力线 位置以一个相对均匀的速度不断移动直至受拉纤维形成开裂的位置。在已经超过开裂荷载 后,随着附加荷载的施加,压力线移动的速度便会降低,且使预应力钢筋束中的应力和合成 的混凝土力开始发生显著的增加。内部弯矩的作用不断变化直到所有压力线的移动都停止。 其后施加的荷载引起的弯矩完全通过相应的、且按比例的内力变化来抵消,正如在钢筋混凝 土的结构中。这个事实,即弹性阶段和塑性阶段的力由基本不同的作用来传送是非常重要的, 且使强度计算变得对所有的设计都是必要的,以确保存在足够的安全系数。这是正确的,即 使弹性阶段的应力可能符合公认的弹性设计准则。 It should be noted that the load deflection curve is close to(接近于)a straight line up to the cracking load and that the curve becomes progressively(逐渐)more curved as the load is increased above the cracking load. The curvature(弯曲)of the load-deflection curve for loads over the cracking load is due to(由于..所造成的)the change in the basic internal resisting moment action that counteracts(抵消)the applied loads, as described above, as well as to plastic strains that begin to take place in the steel and the concrete when stressed to high levels(受到很大压力). 应该注意到荷载挠度曲线在开裂荷载以内是接近直线的,且在超过开裂荷载 后,该曲线随着荷载的增加逐渐变得更弯曲。正如上面所描述的,当超过开裂荷载时,其荷 载-挠度曲线的弯曲是由于抵消施加荷载的基本内部抵抗弯矩作用的变化以及当受到很大压 力时钢筋和混凝土中开始发生的塑性应变所造成的。 In some structures it may be essential that the flexural members remain crack free(保持构件不开 裂)even under significant(明显的)overloads. This may be due to the structures’ being exposed to exceptionally corrosive(特别腐蚀)atmospheres during their useful life(有效寿命). In designing prestressed members to be used in special structures of this type, it may be necessary to compute the load that causes cracking of the tensile flange(受拉翼缘), in order to ensure that adequate safety against cracking is provided by the design. The computation of the moment that will cause cracking is also necessary to ensure compliance with(符合)some design criteria (criterion的复数形式,标准). 在一些结构中,保持受弯构件不开裂可能是必要的,甚至在明显的超载下。这可能是由于结 构在它们的有效寿命期间被暴露在特别腐蚀的空气中的原因。当设计预应力构件用于这种类 型的特殊结构时,可能有必要计算引起受拉翼缘开裂的荷载,以确保该设计提供足够抵抗开 裂的安全性。也有必要计算会导致开裂的弯矩,以确保符合一些设计标准。 Many tests have demonstrated(证明)that the load-deflection curves of prestressed beams are approximately linear(近似直线的)up to and slightly in excess of(稍微超过)the load that causes the first cracks in the tensile flange. (The linearity(直线性)is a function of the rate at which the load is applied.) For this reason, normal elastic-design relationships(关系式)can be used in computing the cracking load by simply determining the load that results in a net(净)tensile stress in the tensile flange (prestress minus the effects of the applied loads) that is equal to the tensile strength of the concrete. It is customary to assume that the flexural tensile strength of the concrete is equal to the modulus of rupture(断裂模量)of the concrete when computing the cracking load. 很多试验证明,在引起受拉翼缘最初开裂的荷载以内或稍微超过时,预应力梁的荷载-挠度 曲线是近似直线的。(直线性是荷载施加速度的函数。)因此,通过简单地确定导致受拉翼缘 中产生一个净的受拉应力的荷载(预应力减去施加荷载的效应 ),普通的弹性设计关系式能 用来计算开裂荷载,其值等于混凝土的抗拉强度。当计算开裂荷载时,习惯上假定混凝土的 受弯抗拉强度等于混凝土的断裂模量。 In should be recognized that the performance(性能)of bonded(有粘结的)prestressed member is actually a function of the transformed section(换算截面)rather than the gross(毛)concrete section. If it is desirable(想要)to make a precise estimate of the cracking load, such as is required in some research work, this effect(影响)should be considered. 应该承认有粘结的预应力构件的性能实际上是一个换算截面的函数,不是混凝 土毛截面的函数。如果想要对开裂荷载作一精确估计,例如在一些研究工作中需要的,该影 响应该被考虑。 Principles of Ultimate Moments Capacity for Bonded members 有粘结的构件极限弯矩能力的规则 When prestressed flexural members that are stronger in shear and bond than in bending are loaded to failure, they fail in one of the following modes(方式): 当剪切和粘结比弯曲强的预应力受弯构件受荷失效时,它们会以下列方式中的 一种失效: (1) Failure at cracking load In very lightly prestressed members, the cracking moment may be greater than the moment the member can withstand in the cracked condition and, hence, the cracking moment is the ultimate moment. This condition is rare(很少的)and is most likely to occur in members that are prestressed concentrically with small amounts of steel. It can also occur in hollow or solid(实心)prestressed concrete members that have relatively low levels of reinforcing. Determination of the possibility of this type of failure is accomplished by comparing the estimated moment that would cause cracking to the estimated ultimate moment, computed as described below. When the estimated cracking load is larger than the computed ultimate load, this type of failure would take place if the member were subjected to the required loads. Because this type of failure is brittle failure, it occurs without warning – designs that would yield(产生)this mode of failure should be avoided. (1)开裂荷载下的失效 在施加非常少量预应力的构件中,其开裂弯矩可能 大于构件在开裂状态下能承受的弯矩,因此,开裂弯矩为极限弯矩。这种情况是很少的,且 在构件中最可能发生用少量钢筋同心地施加预应力。在空心或实心的预应力混凝土构件中也 会出现相对低等级的钢筋。 通过比较引起开裂的弯矩估计值与按下面描述(的方法)计算 的极限弯矩估计值来确定这种失效的可能性。当估计的开裂荷载大于计算的极限荷载,则如 果构件承受要求的荷载,这种失效将会发生。由于这种失效是脆性失效,因此其发生时没有 警告-产生这种失效方式的设计应该被避免。 (2)Failure due to rupture of steel In lightly reinforced(少量加筋)members subjected to ultimate load, the ultimate strength of the steel may be attained before the concrete has reached a highly plastic state(高度塑性状态). This type of failure is occasionally encountered in the design of structures with very large compression flanges in comparison to(与..相比)the amount of prestressing steel, such as a composite(复合)bridge stringer(纵梁). Computation of the ultimate moment of a member subject to this type of failure can be done with a high precision. The method of computation, as well as the determination of which members are subject to this mode of failure, is described below. (2)钢筋断裂引起的失效 在少量加筋并承受极限荷载的构件中,钢筋的极限强 度可能在混凝土达到高度塑性状态之前就达到。这种失效在与预应力筋的数量相比有很大受 压翼缘的结构设计中会偶然遇到,如一个复合的桥梁纵梁。可以高精度地计算易遭受这种失 效的构件的极限弯矩。这种计算方法以及确定哪根杆件易遭受这种失效方式将在下面描述。 (3)Failure due to strain The usual underreinforced(配筋不足), prestressed structure that are encountered in practice are of such proportions(尺寸)that, if loaded to ultimate, the steel would be stressed well into(早已进入)the plastic range and the member would evidence(显示) large deflection. Failure of the member will occur when the concrete attains the maximum strain that it is capable of withstanding. It is important to understand that research into(..的调查)the ultimate bending strength of reinforced and prestressed concrete has led most investigators to the conclusion that concrete, of the quality(特性)normally(通常)encountered in prestressed work (工程)fails when the limiting strain of 0.003 is attained in the concrete. Since the ultimate bending capacity is limited by strain rather than stress in the concrete, it is a function of the elastic moduli(modulus的复数形式,模量)of the concrete and steel. The magnitude of the ultimate moment for members of this category can also be predicted(预测), as a rule, within the normal tolerance(正常的允许误差)expected in structural design. The ultimate moment of underreinforced sections cannot be predicted with the same precision as the lightly reinforced members described above, since the ultimate moments of underreinforced members are a function of the elastic properties of the steel and the effective stresses in the prestressing steel, whereas the ultimate moment capacities of lightly reinforced members are not. (3)应变引起的失效 在实践中遇到通常配筋不足的预应力结构具有这样的尺寸, 以至于如果加荷至极限,钢筋的应力早已进入塑性范围,而该构件将显示出很大的挠度。当 混凝土达到其能承受的最大应变时,该构件将发生失效。明白对预应力钢筋混凝土的极限抗 弯强度的调查已经导致多数调查者得到了结论,即当混凝土达到 0.003的极限应变时,具有 在预应力工程中常遇性能的混凝土会失效,这点很重要。由于极限抗弯能力受到混凝土中的 应变而不是应力的限制,因此,它是混凝土和钢筋弹性模量的函数。作为一个规律,这类构 件极限弯矩的大小也能被预测在结构设计所预期的正常的允许误差范围内。 配筋不足截面 的极限弯矩不能以与上面描述的少量配筋的构件相同的精度来预测,因为配筋不足的构件的 极限弯矩是钢筋弹性性能和预应力钢筋中的有效应力的函数,而少量配筋构件的极限弯矩能 力则不是。 (4)Failure due to crushing of the concrete Flexural members that have relatively large amounts of prestressing steel or relatively small compressive flanges are referred to as being overreinforced(超配筋的). Overreinforced members, when loaded to destruction, do not attain the large deflections associated with underreinforced members – the steel stresses do not exceed the yield point and failure is the result of the concrete being crushed. Computation of the ultimate moments of overreinforced members is done by a trial and error (试算) procedure,involving assumed strain patterns(模式), as well as by empirical relationships(经验关系式). (4)混凝土压碎引起的失效 有着相对大量预应力筋或相对小的受压翼缘的受弯构件 称为是超配筋的。当受荷至破坏的超配筋构件没有达到与配筋不足构件有关联的大挠度-钢 筋的应力没有超过屈服点,因而失效是混凝土被压碎的结果。通过试算过程以及经验关系式 来计算超配筋构件的极限弯矩,包括假定应变模式。 It must be emphasized that there is no clear distinction(明显的区别)between the different classifications(类别)of failure listed above. For convenience of design, certain parameters, which are a function of the percentage of steel, are used by different authorities(权威)to distinguish between the different types of failure that would be anticipated(预测). 必须强调在上面列出的不同的失效类别之间没有明显的区别。为了便于设计, 通过不同的权威采用某些参数(这些参数是钢筋百分率的函数)来区别被预测的不同类型的 失效。 In order to simplify the explanation of the theory related to the computation of the ultimate moments, a rectangular section will be assumed throughout(在整个..的过程中)the derivation, in order to eliminate(消除)the variable(变化因素)of flange width which is frequently encountered with I or T sections. In addition, the following assumptions, some of which differ slightly from those contained in ACI-318, are made: 为了简化与极限弯矩计算有关的理论的解释,在整个推导的过程中将假定一个 矩形截面,以消除翼缘宽度的变化因素,其常常被遇到是I或T形截面。而且,作以下假定, 其中一些稍许不同于ACI-318中包括的假定: Plane sections are assumed to remain plane. The stress-strain properties(特点)of the steel are smooth curves without a definite(确定的)yield point. The limiting strain of the concrete is equal to 0.0034, regardless of the strength of the concrete. The steel and concrete are completely bonded. 假定平截面依然是平面的; 钢筋的应力-应变特点是光滑的曲线,上面没有确定的屈服点; 混凝土的极限应变等于0.0034,不考虑混凝土的强度; 钢筋与混凝土是完全粘结的; The stress diagram of the concrete at failure is such that the average concrete stress is 0.80f’c and the resultant of the stress in the concrete acts at a distance from the extreme fiber equal to 0.42 of the depth of the compression block. The strain in the top fiber under prestress alone(仅仅)is equal to zero. The section is subject to pure bending. The analysis is for the condition of static loads of short duration(持续时间). 在混凝土失效时的应力图中,平均的混凝土应力为0.80 f’c,而混凝土中的应力合力则作用 在离端部纤维的距离为0.42倍的受压区深度处; 仅在预应力作用下顶部纤维的应变等于零; 截面易遭受纯弯; 分析是针对静力荷载在短的持续时间下的情况。 As we stated above, the relationships that were developed are applicable to rectangular sections. These relationships are equally(同样得)accurate for flanged sections(带翼缘的截面), provided (假如)the neutral axis(中性轴)of the section at ultimate is within the limits of the flange. If the neutral axis falls outside of the flange area(区域), the same strains distribution applied(采用) as in the case of rectangular sections, but due to the variable width of the section, the distance to the resultant of the compressive block must be calculated. To facilitate(方便)the calculation of the location of the resultant, the compression block can be assumed to be rectangular rather than curved without introducing significant error(导致重大错误). 正如我们上面所述,那些被提出的关系式适用于矩形截面。假如在极限状态时截面的中性轴 落在翼缘的边界之内,则这些关系式对有翼缘的截面同样得准确。如果中性轴落在翼缘区域 的外面,则采用与矩形情况中相同的应变分布,但是由于截面宽度的变化,必须计算(中性 轴)至压力区合力的距离。为了方便计算合力的位置,可以假定受压区是矩形的,而不是弯 曲的,这不会导致重大的错误。 When small quantities of non-prestressed reinforcement are used in combination with small quantities of prestressed reinforcement, the additional ultimate moment due to the non-prestressed reinforcement can be calculated. For larger amounts of non-prestressed reinforcement or for members with high steel indices(index的复数形式,率), the moment should be determined by trial and error from the basic strain patterns. 当采用少量的非预应力钢筋再加上少量的预应力钢筋,则可以计算由于非预应 力钢筋引起的附加的极限弯矩。对较多数量的非预应力钢筋或具有高钢筋率的构件,其弯矩 应该根据基本的应变模式通过试算来确定。 Examination(研究)will show that small variations(微小变化)in the effective prestress have no significant effect on the ultimate strength of prestressed members. It is important to note that even if errors are made in estimating the losses of prestress, in estimating the stressing(施加应力) friction, or even if the stressing is not carried out to a high precision in the field due to poor workmanship(低劣的手艺), the effect on the ultimate moment is generally small for flexural members with bonded tendons. 研究显示有效预应力的微小变化对预应力构件的极限强度没有显著的影响。很 重要地注意到,即使错误地估计了预应力的损失和施加应力的摩擦,或即使在现场由于低劣 的手艺而没有高精度地施加应力,对有粘结钢筋束的受弯构件极限弯矩的影响通常也是小 的。 Principles of Ultimate Moment Capacity for Unbonded Members 无粘结的构件极限弯矩能力的规则 Because the prestressing tendons can slip (with respect to the concrete) during loading of an unbonded member, the relationships for ultimate moment capacity do not apply to(适用于) unbonded beams. Because the tendons can slip with respect to the concrete, other variables(另外 的变量)affect the ultimate moment capacity of unbonded prestressed concrete members. 由于在对无粘结的构件加荷期间,施加预应力的钢筋束会相对于混凝土滑移, 因此极限弯矩能力的关系式不适用于无粘结的梁。由于该钢筋束会相对于混凝土滑移,因此 另外的变量影响了无粘结的预应力混凝土构件的极限弯矩能力。 Variables that affect the ultimate moment capacity of an unbonded beam, but which do not affect bonded beams in the same manner or not at all(一点也不), include the following: Magnitude of the effective stress in the tendons. Span to depth ratio(跨高比). Characteristics of the materials. Form of loading (shape of the bending moment diagram). Profile(断面)of the prestressing tendon. Friction coefficient between the prestressing steel and duct(导管). Amount of bonded non-prestressed reinforcing. 影响无粘结的梁的极限弯矩能力,但不影响或者根本不影响相同方式下的有粘结的梁的变量 包括如下: 钢筋束中的有效应力大小; 跨高比; 材料特性; 加荷方式(弯矩图的形状); 施加预应力的钢筋束的断面; 在施加预应力的钢筋和导管之间的摩擦系数; 有粘结的非预应力钢筋的数量。 A method of computing the ultimate strength of prestressed members (with unbonded tendons) that takes into account(考虑)the variables listed above has been proposed by Pannell. This method is based upon experimental data and is considered slightly conservative. Pannell已经建议用以计算考虑上述列出变量的(具有无粘结的钢筋束的)预 应力构件极限强度的方法。该法是基于试验数据,并且考虑时稍有保守。 It should be recognized that the ultimate moment capacity of a member stressed with unbonded tendons, unlike members with bonded tendons, may be adversely(反过来)affected by unintentional(不经意的)variations in the effective prestress. Hence, it is considered prudent(谨 慎的)to exert(给予)more care in estimating the losses of prestress and in supervising(监控) the stressing(加压)of unbonded members than would be considered necessary for bonded members, in order to assure the desired results are obtained. 应该承认,不象具有有粘结的钢筋束的构件,受到无粘结的钢筋束施加应力的构件的极限弯 矩能力,可能会反过来受到有效应力不经意的变化的影响。因此,为了确保获得期望的结果, 比起需谨慎考虑有粘结的构件而言,在估计预应力损失和监控无粘结的构件加压时更加予以 小心谨慎,这被认为是谨慎的(做法)。 作业练习 通过一篇Reading Material的学习,进一步了解预应力钢筋束的粘结力。 Unit 10 第十单元 Structure Steel 结构钢 教学目标 了解钢材作为结构材料的优缺点 了解不同性能的结构钢的应力-应变关系 熟悉各种描述结构钢性能、特点的词汇 熟悉科技类文献的常用句型 熟悉sharp 、drastically、substantial、 considerable、extensive、tremendously的不同含 义;decided、appreciably、visible、clearly的不同用法;residual strain、offset strain、 scrap value 的含义;normal、usual、commonly的不同含义;follow的不同含义。 A person traveling in the United States might quite understandably decide(清楚地断定)that steel was the perfect structural material. He or she would see an endless number of(无穷无尽的)steel bridges, buildings, towers, and other structures comprising, in fact, a list too lengthy to enumerate (列举). After seeing these numerous steel structures this traveler might be quite surprised to learn(了解)that steel was not economically made in the United States until late in the nineteenth century and the first wide-flange beams were not rolled(轧制)until 1908. Advantages of Steel as a Structural Material 钢材作为结构材料的优点 一位在美国旅行的人可能会很清楚地断定钢材是理想的结构材料。他或她将看到无穷无尽的钢桥、钢的建筑物、钢塔以及其它的钢结构,实际上包含的名单太长了以至于无法列举。在观看了这些数量众多的钢结构后,这位旅行者可能会非常惊讶地了解到在美国直到19世纪 后期钢材才被经济地制造,并且直到1908年才轧制出第一根宽翼缘的梁。 The assumption of the perfection(完美)of this metal, perhaps the most versatile(通用的)of structural materials, would appear to be even more reasonable(合理的)when its great strength, light weight, ease of fabrication(制作), and many other desirable(理想的) properties are considered(考虑). These and other advantages of structural steel are discussed in detail(详细 地)in the following paragraphs. 当考虑这种金属具有高强、轻质、易制作以及很多其它理想的性能时,认为其完美的假定甚至显得更合理,或许它是最通用的建筑材料。这些和其它的结构钢的优势将在下面的段落中详细地讨论。 High Strength The high strength of steel per unit of weight means that structure weights will be small. This fact is of great importance for long-span bridges, tall buildings, and structures having poor foundation conditions(薄弱地基条件). 高强度 钢材每单位重量的高强度意味着结构的重量将是小的。这个事实对大跨的桥梁、高层建筑以及有着薄弱地基条件的结构具有重要意义。 Uniformity The properties of steel do not change appreciably(明显地)with time, as do those of reinforced-concrete structure. 一致性 钢材的性能随时间的变化不明显,正如钢筋混凝土结构的性能也随时间变化不明显。 Elasticity Steel behaves closer to(更接近于)design assumptions than most materials because it follows(遵循)Hooke’s law up to fairly high stresses. The moments of inertia(惯性矩)of a steel structure can be definitely(确切地) calculated, while the value obtained for a reinforced-concrete structure are rather indefinite(不确切). 弹性 比起大多数材料,钢材的运行更接近于设计的假定,因为它直到相当高的应力仍然遵循虎克定理。一个钢结构的惯性矩可以确切地被计算,而钢筋混凝土结构得到的该值是非常得不确切。 Permanence Steel frames that are properly maintained(维护)will last indefinitely(长期地). Research on some of the newer steels indicates that under certain conditions no painting(涂漆) maintenance whatsoever (一点也不)will be required. 持久性 适当维护的钢框架将会长期地维持下去。对一些较新钢材的研究显示在某些条件下,一点也不需要涂漆的维护。 Ductility The property of a material by which it can withstand extensive(大量的)deformation without failure under high tensile stresses is said to be its ductility. When a mild(低碳)or low-carbon structural steel member is being tested in tension(受拉测试), a considerable(相当 大的)reduction in cross section and a large amount elongation will occur at the point of failure before the actual fracture occurs. A material that does not have this property is generally unacceptable and is probably hard and brittle and might break if subjected to a sudden shock(冲 击). 延性 材料在高的拉应力下能承受大的变形而不破坏的性能被称为是延性。当一根低 碳结构钢构件正在进行受拉测试时,在实际的断裂发生之前,在破坏点处将会发生横断面的 大大缩小以及产生很大的伸长。不具有这种性能的材料通常是不被接受的,并且该材料可能 是坚硬和脆性的,如果承受一个突然的冲击,可能会断裂。 In structural members under normal(正常的)loads, high stress concentrations develop(形成) at various points. The ductile nature of the usual(普通的)structural steels enables them to yield locally at those points, thus preventing premature(过早的)failures. A further(另一个)advantage of ductile structures is that when overloaded their large deflections give visible (明显的) evidence of impending failure(即将破坏的迹象)(sometimes jokingly referred to as “running time” “逃跑时间”). 在正常荷载下的结构构件中,在不同的点上会形成高应力集中。普通结构钢 延性的特点使它们在这些点上局部地屈服,这样阻止了过早的破坏。延性结构的另一个优势 是当超载时,它们的大变形显示出明显的即将破坏的迹象(有时候戏称为“逃跑时间”)。 In Fracture Toughness Structural steels are tough(坚韧的); that is, they have both strength and ductility. A steel member loaded until it has large deformations will still be able to withstand large forces. This is a very important characteristic because it means that steel members can be subjected to large deformations during fabrication and erection(安装)without fracture – thus allowing them to be bent, hammered, sheared(剪切), and have holes punched(冲孔)in them without visible damage. The ability of a material to absorb energy in large amounts is called toughness”). 断裂韧性 结构钢是坚韧的;也就是说,它们既有强度又有延性。一根钢构件加荷至 大变形时将仍然能够承受大的力。这是非常重要的特性,因为这意味着钢构件在制作和安装 期间能承受大的变形而不断裂—这就允许它们被弯曲、锤击、剪切以及在上面冲孔而没有明 显的损害。材料吸收大量能量的能力称为韧性。 Additions to Existing Structures Steel structures are quite well(相当)suited to having additions made to them. New bays(节间)or even entire(整个)new wings(翼)can be added to existing steel frame buildings, and steel bridges may often be widened. 在对已有结构的添加 钢结构相当适合对其自身进行添加。新的节间、甚至整个新的 翼能被添加到已有的钢框架建筑上,因此钢桥常常可以被加宽。 Miscellaneous Several other important advantages of structural steel are: (a) ability to be fastened together by several simple connection devices(方法) including welds and bolts; (b) adaptation to prefabrication(预制); (c) speed of erection; (d) ability to be rolled into a wide variety of (各种各样的) sizes and shapes; (e) fatigue strength; (f) possible reuse(再利用)after a structure is disassembled(分解), and (g) scrap value(残余价值), even though not reusable (可再利用的)in its existing form. Steel is the ultimate recyclable(可循环的)material. 其它 结构钢其它的一些重要优点是:(a)能够通过一些简单的连接方法包括焊缝和 螺栓将其连接起来;(b)适合预制;(c)安装速度;(d)能够轧制成各种各样的尺寸和形状; (e)疲劳强度;(f)在结构被分解后可能的再利用;以及(g)残余价值,即使不能以其已 有的形式被再利用。钢材是最终可循环的材料。 Disadvantages of Steel as a Structural Material 钢材作为结构材料的缺点 In general, steel has the following disadvantages. 通常,钢材具有下列缺点。 Maintenance Costs Most steels are susceptible to(易受..影响)corrosion(锈蚀)when freely (直接地) exposed to air and water and must therefore be periodically(定时地)painted. The use of weathering(风化)steels, in suitable design applications, tends to eliminate(避免)this cost. 维护费用 大多数钢材在直接暴露于空气和水中时容易锈蚀,因此必须被定时地涂漆。在 合适的设计应用中,采用风化的钢材往往能避免该费用。 Fireproofing Costs Although structural members are incombustible(不燃性的), their strength is tremendously(惊人地)reduced at temperatures commonly(通常)reached in fires when the other materials in a building burn. Many disastrous fires(火灾)have occurred in empty buildings where the only fuel(燃料)for the fires was the buildings themselves. Furthermore, steel is an excellent(极好的)heat conductor(导热体), nonfireproofed(不耐火)steel members may transmit enough heat from a burning section or compartment(隔间)of a building to ignite(使..燃烧) materials with which they are in contact in adjoining sections of the building. As a result of these facts the steel frame of a building may have to be protected by materials with certain insulating characteristics, or the building may have to include a sprinkler system(自动喷水灭火系统)if it is to meet the building code requirements of the locality in question(正被讨论的地区). 防火费用 尽管结构构件具有不燃性,但它们的强度通常在火中达到的温度时会惊人地减 少,而建筑中的其它材料则会燃烧。很多火灾发生在空的建筑物中,这里着火的唯一燃料是 建筑物自己。而且,钢材是一个极好的导热体,不耐火的钢构件可以将一个房屋燃烧的区域 或隔间的足够的热量传送而使邻近建筑区域内与之接触的材料燃烧。根据这些现象,建筑物 的钢框架可能不得不采用具有一定绝热性能的材料加以保护,或者该建筑物不得不包含一个 自动喷水灭火系统,假如它符合正被讨论地区的建筑规范的要求。 Susceptibility to Buckling The longer and more slender the compression members, the greater the danger of buckling. As previously indicated, steel has a high strength per unit of weight, but when used for steel columns is not very economical sometimes because considerable material has to be used merely to stiffen(加强)the columns against buckling. 容易屈曲 受压构件越是长和细的,其屈曲的危险越大。正如前面所显示的,钢材单 位重量的强度高,但是用于钢柱时有时并不经济,因为不得不采用相当多的材料仅仅是为了 加强柱子以防屈曲。 Fatigue Another undesirable(不受欢迎的)property of steel is that its strength may be reduced if it is subjected to a large number of stress reversals(反向应力)or even to a large number of variations of tensile stress. (We have fatigue problems only when tension is involved.) The present practice(习惯)is to reduce the estimated strengths of such members if it is anticipated(预测)that they will have more than a prescribed(规定的)number of cycles of stress variation. 疲劳 钢材另一个不受欢迎的特性是如果它承受大量的反向应力或者甚至承受大量 的拉应力的变化,则它的强度可能会降低。(只有包括拉力时我们才有疲劳问题。)目前的习 惯是如果预测到会有超过规定数量的应力变化的循环次数,则应降低该构件的估计强度。 Brittle Fracture Under certain conditions steel may lose its ductility, and brittle fracture may occur at places of stress concentration. Fatigue-type(疲劳型)loadings and very low temperatures aggravate(加重)the situation. 脆性断裂 某些条件下,钢材可能失去它的延性,并且可能在应力集中处发生脆性断 裂。疲劳型荷载和非常低的温度加重了这种情形。 Stress-strain Relationships in Structural Steel 结构钢中的应力-应变关系 In order to understand the behavior of steel structures, it is absolutely essential for the designer to be familiar with the properties of steel. Stress-strain diagrams present valuable(有价值的) information necessary to understand how steel will behave in a given situation. Satisfactory steel design methods cannot be developed(得到)unless complete information is available concerning the stress-strain relationships of the material being used. 为了解钢结构的性能,设计人员绝对有必要熟悉钢材的性能。应力-应变图显示了有价 值的信息,它对理解钢材在一个给定的条件下如何运行是必要的。除非获得关于正被使用的 材料的应力-应变关系的完整的信息,否则就不能得到满意的钢材设计方法。 If a piece of(一段)ductile structural steel is subjected to a tensile force it will begin to elongate. If the tensile force is increased at a constant(不变的)rate, the amount of elongation will increase constantly(不断地)within certain limits(范围). In other words, elongation will double when the stress goes(变成)from 6,000 to 12,000 psi (pounds per square inch). When the tensile stress reaches a value roughly(大约)equal to one-half of the ultimate strength of the steel, the elongation will begin to increase at a greater rate without a corresponding increase in the stress. 如果一段延性结构钢承受一个拉力,它便开始伸长。如果该拉力以一个不变的速度增加, 则伸长值将在一定的范围内不断地增加。换句话说,当应力从6000磅每平方英寸变成12000 磅每平方英寸时,伸长将加倍。当拉应力达到的值约等于钢材极限强度的一半时,伸长开始 以一个较大的速度增加,而应力没有相应的增加。 The largest stress for which Hooke’s law applies(适用)or the highest point on the straight-line portion of the stress-strain diagram is the proportional limit(比例极限). The largest stress that a material can withstand without being permanently(永久地)deformed is called the elastic limit (弹性极限). This value is seldom actually measured and for most engineering materials including structural steel is synonymous with(与..意思相同)the proportional limit. For this reason the term proportional elastic limit is sometimes used. 虎克定理适用的最大应力或者应力-应变图的直线部分的最高点是比例极限。一种材料 能承受的且不发生永久变形的最大应力称为弹性极限。这个值实际上很少被测出,而且对包 括结构钢在内的大多数工程材料来说,该值与比例极限同义。因此,术语弹性比例极限有时 被采用。 The stress at which there is a decided(明显的)increase in the elongation or strain without a corresponding increase in stress is said to be the yield stress. It is the first point on the stress-strain diagram where a tangent to(..的切线)the curve is horizontal. The yield stress is probably the most important property of steel to the designer, as so many(很多的)design procedures are based on this value. Beyond the yield stress there is a range in which a considerable increase in strain occurs without increase in stress. The strain that occurs before the yield stress is referred to as the elastic strain; the strain that occurs after the yield stress, with no increase in stress, is referred to as the plastic strain. Plastic strains are usually from 10 to 15 times the elastic strains. 在某个应力上伸长或应变有明显的增加而应力没有相应的增加,该应力称为屈服应力。它是 应力-应变图上其所在曲线的切线是水平的第一个点。对设计者来说,屈服应力可能是钢材 的最重要的特性,因为很多的设计方法是基于该值的。超过屈服应力后,有一段范围中应变 发生相当大的增加而应力没有增加。屈服应力发生之前的应变称为弹性应变;屈服应力发生 之后的没有应力增加的应变称为塑性应变。塑性应变通常是弹性应变的10到15倍。 Yielding of steel without stress increase may be thought to be a severe disadvantage when(而)in actuality(实际上)it is a very useful characteristic. It has often performed the wonderful(出色 的)service of preventing failure due to omissions(忽略)or mistakes on the designer’s part(在.. 方面). Should(倒装,表示如果..) the stress at one point in a ductile steel structure reach the yield point, that part of the structure will yield locally without stress increase, thus preventing premature failure. This ductility allows the stresses in a steel structure to be readjusted(重新调整). Another way of describing this phenomenon is to say that very high stresses caused by fabrication, erection, or loading will tend to equalize(使..平衡) themselves. It might also be said that a steel structure has a reserve(储备)of plastic strain that enables it to resist overloads and sudden shocks. If it did not have this ability, it might suddenly fracture, like glass or other vitreous(玻璃质的) substances. 没有应力增加的钢材屈服可能被认为是一个严重的缺点,而实际上它是一个非常有用的特 性。它已常常有效地防止了由于设计者方面的忽略或错误而导致的破坏。如果延性钢结构中 的某一点应力达到屈服点,则该结构部分将局部屈服而没有应力的增加,这样便阻止了过早 破坏。延性允许钢结构中的应力进行再调整。另一种描述这个现象的方法是说由制造、安装 或加荷引起的非常高的应力将往往使它们自身得到平衡。也可以说钢结构具有塑性应变的储 备以使它能抵抗超载和突然的冲击。如果它不具有该能力,它可能会象玻璃或其它玻璃质的 物质那样突然断裂。 Following(在..之后)the plastic strain there is a range in which additional(额外的)stress is necessary to produce additional strain. This is called strain-hardening. This portion of the diagram is not too important to today’s designer because the strains are so large. A familiar stress-strain diagram for mild or low-carbon structural steel is shown in Fig. 10-1. Only the initial part of the curve is shown here because of the great(很多的)deformation which occurs before failure. At failure in the mild steels the total strains are from 150 to 200 times the elastic strains. The curve will actually continue up to its maximum stress value and then “tail off”(减小)before failure. A sharp(急剧的)reduction in the cross section of the members takes place (called “necking”颈 缩) followed by failure. 塑性应变后有一段范围,在该段范围内要产生额外的应变必须有额外的应力。这段称为应变 硬化。这部分图对今天的设计者来说不太重要,因为应变太大了。一张熟悉的低碳结构钢的 应力-应变图如图10-1所示(图10-1是典型的低碳结构钢在室温下的应力-应变图)。这里只 显示了曲线的初始部分,因为很多的变形发生在失效之前。在低碳钢失效时,总的应变是弹 性应变的150到200倍。曲线实际上将继续至它的最大应力值,然后在破坏之前应力变小。 紧接着构件的破坏,其横截面会发生急剧的减小(称为颈缩)。 The stress-stain curve of Fig.10-1 is typical of(对..是典型的)the usual ductile structural steel and is assumed to be the same for members in tension or compression. (The compression members must be stocky(粗短的)because slender compression members subjected to compression loads tend to bend laterally(侧向地), and their properties are greatly affected by the bending moments so produced.) The shape of the diagram varies with the speed of loading, the type of steel, and the temperature. One such variation is shown in the figure by the dotted line(虚线)marked upper yield(标明屈服上限). This shape stress-strain curve is the result when a mild steel has the load applied rapidly, while the lower yield is the case for slow loading. 图10-1中的应力-应变曲线对一般的延性结构钢来说是典型的,并假定构件在受拉和受压时 是相同的。(受压构件必须是粗短的,因为细长的受压构件承受压力时往往会侧向弯曲,且 它们的性能大大地受这样形成的弯矩的影响。)图的形状随加荷的速度、钢材的类型和温度 而变化。这样的一个变化通过一根标明屈服上限的虚线显示在图中。该应力-应变曲线的形 状是低碳钢快速加载的结果,而屈服下限是缓慢加载的情况。 You should note that the stress-strain diagram of Fig.10-1 was prepared for(为..而准备)mild steel at room temperature. Steels (particularly those with rather high carbon contents) may actually increase a little in strength as they are heated to a temperature of about 700?(Fahrenheit). As temperatures are raised into the 800? to 1000? range, steel strengths are drastically(急剧地) reduced, and at 1200? they have little strength left. 你应该注意到图10-1中的应力-应变图是用于室温下的低碳钢。当钢材(特别是那些有 着相当高的碳含量的钢材)被加热至温度大约为700?时,其强度实际上可能会增加一些。 当温度被升高至800? 到 1000?的范围时,钢材的强度急剧地减少,而在1200?时几乎不 再有强度。 Typical ratios(比值)of yield stresses at high temperatures to yield stresses at room temperatures are approximately 0.77 at 800?, 0.63 at 1000?, and 0.37 at 1200?. Temperatures in these ranges can be easily reached in steel members during fires, in localized areas of members when welding is being performed, in members in foundries(铸造车间)over open flame(明火), and so on. 高温下的屈服应力与室温下的屈服应力的典型比值,在800?时约为0.77,在1000?时 约为0.63,而在1200?时约为0.37。燃烧中的钢构件、正在进行焊接的构件的局部区域、 铸造车间中明火上的构件等等,是很容易达到这段范围的温度。 When steel sections(钢部件)are cooled below 32?, their strengths will increase a little, but they will have substantial(显著的) reductions in ductility and toughness. 当钢部件被冷却至32?以下时,它们的强度将增加一些,但延性和韧性将显著地减少。 A very important property of a structure which has not been stressed beyond its yield point is that it will return to its original length when the loads are removed. Should it be stressed beyond this point it will return only part of the way to its original position. This knowledge leads to the possibility of testing an existing structure by loading and unloading. If after the loads are removed, the structure will not resume(恢复)its original dimensions, it has been stressed beyond its yield point. 在一个结构所受的应力未超过其屈服点时,一个很重要的结构性能是当移去荷载时,它 将恢复至其初始的长度。如果它所受的应力超过该点时,则将部分返回至其初始的位置。这 个知识导致有可能通过加载和卸载来测试现有的结构。如果移去荷载后,该结构没有恢复其 初始的尺寸,则它所受的应力已经超过了其屈服点。 Steel is an alloy consisting almost entirely of iron (usually over 98 percent). It also contains small quantities of carbon, silicon(硅), manganese(锰), sulfur(硫), phosphorus(磷), and other elements(元素). Carbon is the material that has the greatest effect on the properties of steel. The hardness and strength increase as the carbon percentage is increased, but unfortunately the resulting steel is more brittle and its weldability(可焊性)is adversely affected(不利影响). A smaller amount of carbon will make the steel softer and more ductile, but also weaker. The addition of such elements as chromium(铬), silicon, and nickel(镍)produces steels with considerably higher(高得多的)strengths. Though frequently quite useful, these steels, however, are appreciably more expensive and often are not as easy to fabricate. 钢材是一种合金,几乎完全由铁组成(通常超过98%)。它也包含少量的碳、硅、锰、硫、 磷和其它一些元素。碳是对钢材的性能影响最大的材料。硬度和强度随着碳的百分比的增加 而提高,但不幸的是导致钢材较脆,且它的可焊性受到不利影响。较少量的碳会使钢材变得 较软和更延性,但也较弱。添加诸如铬、硅、镍等元素使制造的钢材具有高得多的强度。虽 然这些钢材常常极为有用,但是价格明显更昂贵,并且常常难以制造。 A typical stress-strain diagram for a brittle steel is shown in Fig.10-2. Unfortunately, low ductility or brittleness is a property usually associated with high strengths in steels (although not entirely confined to(限于)high-strength steels). As it is desirable(理想的)to have both high strength and ductility, the designer may have to decide between(在两者中选择其一)the two extremes(极端) or to compromise(妥协). A brittle steel may fail suddenly without warning when overstressed, and during erection could possibly fail due to the shock(振动)of erection procedures(过程). 脆性钢材典型的应力-应变图如图10-2所示(图10-2是典型的脆性钢材的应力-应变图)。 很不幸,在钢材中低延性或脆性是一个通常与高强度联系在一起的性能(尽管不完全限于高 强钢材)。由于既有高强度又有延性是理想的状态,因此,设计者可能不得不在两个极端之 间进行选择或者决定妥协。脆性钢材在超载时可能会突然破坏而没有警告,并且在安装期间 可能会由于安装过程中的振动而破坏。 Brittle steels have a considerable(相当大的)range where stress is proportional to strain, but do not have clearly defined(明确定义的)yield stresses. Yet, to apply(应用)many of the formulas given in structural steel design specifications, it is necessary to have definite(明确的)yield stress values regardless of whether the steels are ductile or brittle. 脆性钢材在一段相当大的范围内其应力与应变是成比例的,但没有明确定义的屈服应 力。但是,为了应用在结构钢设计规范中给出的多数公式,有必要有一个明确的屈服应力值 而不管钢材是延性还是脆性。 If a mild steel member is strained beyond its elastic limit and then unloaded, it will not return to a condition of zero strain. As it is unloaded, its stress-strain diagram will follow(沿着)a new path (shown by the dotted line in Fig. 10-2) parallel to the initial straight line. The result is a permanent or residual strain. 如果低碳钢构件达到的应变超过其弹性极限,然后卸载,它将不再恢复到零应变的状态。 当它卸载时,它的应力-应变图将沿着一条平行于初始直线的新的途径(图10-2中显示的虚 线)。这个结果是一个永久应变或残余应变。 The yield stress for a brittle steel is usually defined as the stress at the point of unloading which corresponds to some arbitrarily defined (任意规定的)residual strain (0.002 being the common value). In other words, we increase the strain by a designated(指定的)amount and draw a line from that point, parallel to the straight-line portion of the stress-strain diagram, until the new line intersects the old. This intersection is the yield stress at that particular strain. If 0.002 is used, the intersection is usually referred to as the yield stress at 0.2 percent offset strain(残余应变). 脆性钢材的屈服应力通常定义为卸载点的应力,它相应于某一个任意规定的残余应变 (常用值为0.002)。换句话说,我们使应变增加一个指定量,然后从该点画出一根线,平行 于应力-应变图的直线部分,直到新老线相交。该交点是那个特定应变时的应力。如果采用 0.002,该交点通常称为残余应变为0.2%时的屈服应力。 作业练习 通过一篇Reading Material的学习,进一步了解钢结构的发展和设计,包括现代结构钢不同 类型的比较、钢构件经济的设计方法、计算机在设计中的应用等。 Unit 11 第十一单元 Steel Members 钢构件 教学目标 了解受拉钢构件的特点和断面形式 了解轴压钢构件的受力特点和失效模式 熟悉各种钢构件的名称、性能、特点的词汇 熟悉科技类文献的常用句型 熟悉bars、sections、shapes的含义;flaw、imperfection、defect的含义;flexural、buckle、 twist、bend、crookedness的不同含义;angle、tee、channel的不同含义;joist、lintel、spandrel、 stringer、floor beam、girder的不同含义;flexibility的不同含义;section的不同含义。 Tension members are found in bridge and roof trusses (屋架), towers, bracing systems, and in situation where they are used as tie rods(连杆). The selection of a section to be used as a tension member is one of the simplest problems encountered in design. As there is no danger of buckling, the designer needs only to compute the factored force(分解力)to be carried by the member and divide that force by a design stress to determine the effective cross-sectional area required. Then it is necessary to select a steel section(截面)that provides the required area. Though these introductory(介绍性的)calculations for tension members are quite simple, they do serve(完成) the important tasks(目标) of getting students started with design ideas(概念)and getting their “feet wet” regarding(涉足于) the massive(大量的)LRFD Manual. 1. Tension Members 受拉构件 受拉构件在桥梁和屋架、塔、支撑系统以及用作连杆时被见到。用作受拉构件的截面选择是 设计中遇到的最简单的问题之一。因为没有屈曲的危险,设计者只需要计算由该构件承受的 分解力,并将该力除以设计应力以确定所需的有效横截面面积。然后有必要选择一个钢截面, 它提供了需要的面积。尽管这些关于受拉构件的介绍性的计算非常简单,但它们确实完成了 这样一个重要的目标,即使学生开始拥有设计的概念,并使他们涉足于大量的LRFD手册。 One of the simplest forms(形式)of tension members is the circular rod(圆钢), but there is some difficulty in connecting it to many structures. The rod has been used frequently in the past, but has only occasional uses today in bracing systems, light trusses, and in timber construction. One important reason rods are not popular with(受..欢迎)designers is that they have been used improperly(不恰当地)so often in the past that they have a bad name(落得坏名声); however, if designed and installed correctly, they are satisfactory for many situations. 受拉构件最简单的形式之一是圆钢,但是将其与很多结构连接有一些困难。过去常 常采用圆钢,但是如今只偶然用于支撑系统、轻质桁架以及木结构。圆钢不受设计者欢迎的 一个重要原因是过去常常被不恰当地使用,以至于落得坏名声;但是如果正确地设计和安装, 它们在很多情况下是令人满意的。 The average(通常)size rod has very little(几乎没有) stiffness and may quite easily sag(下 垂)under its own weight(自重), injuring(破坏)the appearance of the structure. The threaded rods formerly used in bridges often worked loose(松掉)and rattled(发出嘎嘎声). Another disadvantage of rods is the difficulty of fabricating them with the exact lengths required and the consequent(随之发生的)difficulties of installation. 通常尺寸的圆钢几乎没有刚度,并且在自重下很容易下垂,因而破坏了结构的 外观。以前用于桥梁的有螺纹的圆钢常常松掉,并发出嘎嘎声。圆钢的另一个缺点是难以按 需要的精确长度来制作,随之发生的是安装的困难。 When rods are used in wind bracing(抗风支撑) it is a good practice(作法)to produce initial tension(初张力)in them, as this will tighten up(拉紧)the structure and reduce rattling and swaying. To obtain initial tension the member may be detailed(设计)shorter than their required lengths, a method that gives the steel fabricator very little trouble. A common rule of thumb(单凭 经验的方法)used is to detail the rods about 1/16 in. short for each 20 ft. of length. (Approximate stress f = εE = [1/16(12)(20)](29×106)= 7550 psi.) Another very satisfactory method involves tightening the rods with some sort of sleeve nut(套筒螺母)or turnbuckle(套筒螺母). Part 8 of the LRFD Manual provides detailed information for these devices(方法). 当圆钢被用作抗风支撑时,一个很好的做法是使它们产生初张力,因为这将拉紧结构,并减 少发出嘎嘎声和摇晃。为获得初张力,杆件可以设计得比它们需要的长度短,该法对钢材的 制作者来说几乎没什么麻烦。一个常用的经验法是设计该圆钢时每20英尺的长度缩短约 1/16英寸。(近似应力f = εE = [1/16(12)(20)](29×106)= 7550 psi.)另一个非常令人满意的 方法包括采用某种套筒螺母拉紧圆钢。LRFD手册的第八部分提供了有关这些方法的详细信 息。 The preceding discussion on rods should illustrate why rolled shapes(轧制型钢)such as angles have supplanted(代替) rods for most applications. In the early days of steel structures, tension members consisted of rods, bars(型钢), and perhaps cables(索). Today, although the use of cables is increasing for suspended-roof(悬索屋顶)structures, tension members usually consist of single(单)angles, double(双)angles, tees(T形钢), channels(槽钢), W sections(型钢), or sections built up from plates(薄钢板)or rolled shapes. These members look better than the old ones, are stiffer, and are easier to connect. Another type of tension section(构件) often used is the welded tension plate or flat bar(扁钢), which is very satisfactory for use in transmission towers(发射塔), signs(广告牌), foot bridges(人行桥), and similar structures. 前面关于圆钢的讨论应该阐明为什么诸如角钢的轧制型钢已在多数应用中代替了圆钢。在早 期的钢结构中,受拉构件包括圆钢、型钢以及可能是索。今天尽管索在悬索屋顶结构中的使 用不断增加,受拉构件通常包括单角钢、双角钢、T形钢、槽钢、W型钢,或由薄钢板或 轧制型钢组合成的型钢。这些构件看上去比老的更好、更结实、更容易连接。另一种常用的 受拉构件是焊接的受拉薄钢板或者是扁钢,它在用于发射塔、广告牌、人行桥以及类似的结 构中是非常令人满意的。 The tension members of steel roof trusses may consist of single angles as small as 21/2 × 2 × 1/4 for minor members. A more satisfactory member is made from two angles placed back to back(背对背)with sufficient space between them to permit the insertion of plates(金属板)(called gusset plates节点板) for connection purposes. Where steel sections(型钢)are used back-to-back in this manner, they should be connected every(每隔)4 or 5 ft. to prevent rattling, particularly in bridge trusses. Single angles and double angles are probably the most common types of tension members in use. Structural tees make very satisfactory chord members (弦杆) for welded trusses because web members (腹杆) can conveniently be connected to them. 钢屋架的受拉构件由单角钢组成,对次要构件其尺寸可小至2 1/2 × 2 × 1/4 。一种较满 意的构件是由两根背对背放置、中间有足够的间距允许插入金属板(称为节点板)以用于连 接的角钢制成。在型钢采用背对背的方式处,它们应该每隔4或5英尺连接一下以免发出嘎 嘎声,特别是在桥梁桁架中。单角钢和双角钢可能是受拉构件中最常用的类型。对焊接桁架 用结构T形钢可得到满意的弦杆,因为腹杆能方便地与它们连接起来。 For bridges and large roof trusses tension members may consist of channels, W or S shapes, or even sections built up from some(某种)combination of angles, channels, and plates. Single channels are frequently used, as they have little eccentricity(偏心)and are conveniently connected. Although, for the same weight, W sections are stiffer than S sections, they may have a connection disadvantage in(由于)their varying depths. For instance, the W12 × 79, W12 × 72, and W12 × 65 all have slightly(略微)different depths (12.38 in., 12.25 in., and 12.12 in., respectively) while the S sections of a certain(某个)nominal size(名义尺寸)all have the same depths. For instance, the S12 × 50, the S12 × 40.8 and the S12 × 35 all have 12.00 in. depths. 对桥梁和大型屋架,受拉构件可以由槽钢、W型钢或S型钢,或者甚至由角钢、槽钢和薄 钢板的某种组合而成的型钢组成。单槽钢常常被采用,因为它们几乎没有偏心,且容易连接。 尽管相同重量的W型钢比S型钢更结实,但W型钢由于其变化的厚度可能存在连接上的不 利条件。例如W12 × 79、 W12 × 72以及 W12 × 65都有略微不同的厚度(分别为12.38 英寸、 12.25 英寸以及 12.12 英寸),而有着某个名义尺寸的S型钢都有相同的厚度。例 如,S12 × 50、S12 × 40.8 以及 S12 × 35,其厚度都为12英寸。 Although single(单个)structural shapes are a little more economical than built-up sections, the latter are occasionally used when the designer is unable to obtain sufficient area or rigidity from single shapes. Where built-up sections are used it is important to remember that field(现场) connections will have to be made and paint applied; therefore, sufficient space must be available to accomplish these things. 尽管单个结构型钢比组合的型钢稍微更经济一些,但是当设计者采用单个型钢不能够得 到足够的面积或刚度时,偶然也会采用后者。在采用组合型钢处,要记住很重要的一点是将 不得不进行现场连接,并进行涂漆;因此,必须获得足够的空间来完成这些事情。 Members consisting of more than one section(截面)need to be tied(连接) together. Tie plates (also called tie bars) located(设置)at various intervals(间隔)or perforated cover plates(多 孔盖板)serve to(用以)hold the various pieces in their correct positions. These plates serve to correct(调整)any unequal(不平衡)distribution of loads between the various parts. They also keep the slenderness ratios(长细比)(to be discussed) of the individual parts within limitation and they may permit easier handling of the built-up members. Long individual members such as angles may be inconvenient(困难的)to handle due to flexibility(易弯性), but when four angles are laced(绑)together into one member, as shown in Fig. 11-1, the member has considerable stiffness. None of the intermittent(间断的)tie plates may be considered to increase the effective areas of the sections. As they do not theoretically carry portions of the force in the main sections, their sizes are usually governed by specifications and perhaps by some judgment on the designer’s part. Perforated cover plates are an exception to(..之例外)this rule, as part of their areas can be considered as being effective in resisting axial load. 由几个截面组成的构件需要连接在一起。以不同的间隔设置的连接板(也称为连杆)或多孔 盖板用以保持不同的构件均在其恰当的位置上。这些板用以调整不同部分之间的荷载分配的 不平衡。它们也使单个部分的长细比(将要讨论)保持在限制的范围内,这样他们可以允许 较容易地处理组合构件。长长的单个构件如角钢,由于易弯性可能处理时有困难,但是当四 根角钢绑扎成一根构件时,如图11-1所显示的,该构件具有相当大的刚度。可以不考虑间 断的连接板对截面的有效面积的增加。因为他们理论上不承受主截面中的部分力,它们的尺 寸通常由规范以及可能根据设计者方面的某些判断来决定。多孔盖板则是该规则的例外,因 为它们的部分面积在抵抗轴向荷载时可认为是有效的。 A few of the various types of tension members in general use are illustrated in Fig. 11-1. In this figure the dotted lines represent the intermittent tie plates or bars used to connect the shapes. 常用的不同类型的一些受拉构件被举例在图11-1中。在该图中虚线代表了用 以连接型钢的间断的连接板或连杆。 Steel cables are made with special steel alloy wire ropes(特种合金钢丝绳) which are cold-drawn(冷拉)to the desired diameter. The resulting wires with strengths of about 200,000 to 250,000 psi can be economically used for suspension bridges(悬索桥), cable supported(悬索) roofs, ski lifts(运送滑雪者上山坡的吊索设备), and other similar applications. 钢索是由冷拉至需要直径的特种合金钢丝绳制成的。形成的具有强度约为200,000 到250,000 psi的钢丝能经济地用于悬索桥、悬索屋顶、运送滑雪者上山坡的吊索设备以及 其他类似的应用。 Normally, to select a cable tension member the designer uses a manufacturer’s catalog(制造商 的产品目录). From the catalog the yield stress of the steel and the cable size required for the design force are determined. It is also possible to select clevises(马蹄钩)or other devices(装置) to use for connectors(连接器)at the cable ends. 通常,为选择索的受拉构件,设计者采用制造商的产品目录。从产品目录中可 以确定钢材的屈服应力和设计力所需要的索的尺寸。也有可能选择马蹄钩或其他的装置用作 索端的连接器。 2.Axially Loaded Compression Members 轴压构件 There are several types of compression members, the column being the best known(知明的). Among the other types are the top chords(上弦)of trusses, bracing members, the compression flanges of rolled beams and built-up beam sections(截面), and members that are subjected simultaneously to bending and compressive loads. Columns are usually thought of as being straight vertical members whose lengths are considerably greater(大得多)than their thicknesses. Short vertical members subjected to compressive loads are often called struts(支柱) or simply compression members; however, the terms column and compression member will be used interchangeably(交替地)in the pages that follow. 有多种受压构件,其中柱子是最知明的。在其他的类型中有桁架的上弦杆、支撑杆件、轧制 梁和组合梁截面的受压翼缘以及同时承受弯曲荷载和压力荷载的构件。柱子通常被认为是直 的竖向构件,其长度比它的厚度大得多。承受压力的短的竖向构件常常称为支柱或简单地称 为受压构件;但是术语柱子和受压构件在下面的页面中将被交替地使用。 There are three general modes(一般模式)by which axially loaded columns can fail. These are flexural buckling, local buckling and torsional buckling. These modes of buckling are briefly defined below. (1)Flexural buckling (also called Euler buckling欧拉屈曲) is the primary type of buckling. Members are subject to flexure or bending when they become unstable(不稳定的). (2)Local buckling occurs when some part or parts of the cross section of a column are so thin that they buckle locally in compression before the other modes of buckling can occur. The susceptibility(敏感性)of a column to local buckling is measured by the width-thickness ratios(宽厚比)of the parts of its cross section. (3)Torsional buckling may occur in columns that have certain cross-sectional configurations(外形). These columns fail by twisting(扭曲)(torsion) or by a combination of torsional and flexural buckling. 轴向受力的柱子发生失效有三种一般的模式。它们是弯曲屈曲、局部屈曲和扭转屈曲。这些 屈曲模式简单地定义如下: (1)弯曲屈曲(也称为欧拉屈曲)是主要的屈曲类型。当构件变得不稳定时,它们易于弯 曲。 (2)局部屈曲发生在柱子某部分的横截面太薄了以至于在其他屈曲模式发生之前它们便受 压局部屈曲。柱子对局部屈曲的敏感性可以通过该部分的横截面的宽厚比来测得。 (3)扭转屈曲可以发生在具有某种横截面外形的柱子中。这些柱子由于扭曲(扭转)或扭 转屈曲与弯曲屈曲的组合而失效。 The longer a column becomes for the same cross section the greater becomes its tendency(趋势) to buckle and the smaller becomes the load it will support. The tendency of a member to buckle is usually measured by its slenderness ratio, which has previously been defined as the ratio of the length of the member to its least radius of gyration(回转半径). The tendency to buckle is also affected by such factors as the types of end connections, eccentricity of load application, imperfection(缺陷)of column material, initial crookedness(弯曲)of column, residual stresses from manufacture, etc. 相同横截面的柱子越长,则屈曲的趋势越大,它能承受的荷载将越小。构件屈曲的 趋势通常根据其长细比来测定,它在先前已定义为构件的长度与它最小的回转半径之比。屈 曲的趋势也受到诸如端部连接的类型、荷载施加的偏心距、柱子材料的缺陷、柱子的初始弯 曲、制造引起的残余应力等因素的影响。 The loads supported by a building column are applied by the column section above(在..上方)and by the connections of other members directly to the column. The ideal situation is for the loads to be applied uniformly across the column, with the center of gravity(重心)of the loads coinciding with(与..一致)the center of gravity of the column. Furthermore, it is desirable(希望)for the column to have no flaws(缺陷), to consist of a homogeneous(均匀的)material, and to be perfectly straight, but these situations are obviously impossible to achieve. 建筑物中的柱子承受的荷载是由其上方的柱子部分和直接与柱子相连的其他构件 施加的。理想的情况是该荷载均匀地施加在柱子上,荷载的重心与柱子的重心一致。而且希 望柱子没有缺陷、由均匀的材料组成以及是完全笔直的,但是这些情形显然不可能达到。 Loads that are exactly centered(居中)over a column are referred to as axial or concentric(同轴 的)loads. The dead loads may or may not be concentrically placed over an interior building column and the live loads may never be centered. For an outside column the load situation is probably even more eccentric(偏心), as the center of gravity of the loads will usually fall well on(恰好落在)the inner side of the column. In other words, it is doubtful that a perfect axially loaded column will ever be encountered in practice. 在柱子上精确居中的荷载称为轴向或同轴荷载。恒载可能或不一定同轴地置于建筑 屋内部的柱子上,而活载可能永远也不会居中。外部柱子的荷载情形甚至可能更偏心,因为 荷载的重心通常恰好落在柱子的内侧。换句话说,在实际中曾遇到一个完全轴向受荷的柱子 是令人怀疑的。 The other desirable situations are also impossible to achieve because of the following: imperfections of cross-sectional dimensions, residual stresses, holes punched for bolts, erection stresses, and transverse loads. It is difficult to take into account all of these imperfections in a formula. 由于下列的原因,其他希望的情形也是不可能达到:横截面尺寸的缺陷;残余应力;螺 栓冲孔;安装应力;横向荷载。很难在一个公式中考虑所有的这些缺陷。 Slight(微小的)imperfections in tension members and beams can be safely disregarded(忽略) as they are of little consequence(后果). On the other hand(相反), slight defects(缺陷)in columns may be of major significance(重大意义). A column that is slightly bent at the time it is put in place(就位)may have significant(很大的)bending moments equal to the column load times the initial lateral deflection. 受拉构件和梁中微小的缺陷可以安全地忽略掉,因为它们几乎没有什么后果。相反, 柱子中微小的缺陷可能意义重大。柱子就位时的轻微弯曲可能产生很大的弯距,它等于柱子 上的荷载乘以初始的横向挠度。 Obviously, a column is a more critical(关键的)member in a structure than is a beam or tension member because minor(较小的) imperfections in materials and dimensions mean a great deal. The fact can be illustrated by a bridge truss that has some of its members damaged by a truck. The bending of tension members probably will not be serious as the tensile loads will tend to straighten(使..伸直)those members; but the bending of any compression members is a serious matter(问 题), as compressive loads will tend to magnify(扩大)the bending in those members. 显然,比起梁或受拉构件,结构中的柱子是较为关键的构件,因为材料和尺寸中较 小的缺陷意味着很多。该事实可通过一个桥梁桁架来说明,其有一些被卡车损坏的构件。受 拉构件的弯曲可能不是严重的问题,因为拉力往往使这些构件伸直;但是任何受压构件的弯 曲则是一个严重的问题。因为压力往往扩大了这些构件中的弯曲。 The preceding(前述的)discussion should clearly show that column imperfections cause them to bend and the designer must consider stresses due to those moments as well as due to axial loads. 前述的讨论应该清楚地表明是柱子的缺陷使它们弯曲,并且设计者必须考虑由于这 些弯距和轴向力引起的应力。 The spacing(间距)of columns in plan establishes(确定)what is called a bay(开间). For instance, if the columns are 20 ft. on center in one direction and 25 ft. in the other direction the bay size is 20 ft ×25 ft.. Larger bay sizes increase the user’s flexibility(灵活性)in space planning. As to economy, a detailed study by John Ruddy indicates that when shallow spread footings(扩展基础) are used, bays with length-to-width ratios of about 1.25 to 1.75 and areas of about 1000 sq ft. are the most cost efficient(费用最经济). When deep foundations are used, his study shows that larger bay areas are more economical. 平面上柱子的间距确定了什么是一个开间。例如如果柱子在某个方向的中心距为20英尺, 在另一个方向的中心距为25英尺,则开间尺寸为20 英尺×25英尺。较大的开间尺寸加大 了使用者在空间布置时的灵活性。就经济性而言,John Ruddy 进行的详细研究表明,当采 用浅的扩展基础时,长宽比约为1.25至1.75的开间、面积约为1000平方英尺是费用最经济 的。当采用深基础时,他的研究显示较大的开间面积更经济。 Type of Beams Beams are usually said to(被认为) be members that support transverse loads. They are probably thought of as being used in horizontal positions and subjected to gravity of vertical loads; but there are frequent exceptions – rafters(椽子), for example. 3. Beams 梁 梁的种类 梁通常被认为是支撑横向荷载的构件。它们可能被认为是用于水平位置,并且承受 竖向的重力荷载;但是常常有例外-例如椽子。 Among the many types of beams are joists(搁栅), lintels(过梁), spandrels(托梁), stringers (纵梁), and floor beams(横梁). Joists are the closely spaced beams supporting the floors and roofs of building, while lintels are the beams over openings in masonry walls such as windows and doors.A spandrel beam supports the exterior walls of buildings and perhaps part of the floor and hallway(走廊)loads. The discovery that steel beams as a part of a structural frame could support masonry walls (together with the development of passenger elevators) is said to(据说) have permitted(使..成为可能)the construction of today’s “skyscrapers”. Stringers are the beams in bridge floors(桥面)running parallel to the roadway(车道), whereas floor beams are the larger beams in many bridge floors which are perpendicular to the roadway of the bridge and are used to transfer the floor loads(板面荷载) from the stringers to the supporting girders(大梁)or trusses. The term girder is rather loosely(不严格)used but usually indicates a large beam and perhaps one into which smaller beams are framed(构成). These and other types of beams are discussed in the sections(章节)to follow. 在很多梁的类型中有搁栅、过梁、托梁、纵梁和横梁。搁栅是支撑建筑物楼面和屋面的密布 梁,而过梁是在砌体墙中诸如窗洞和门洞以上的梁。托梁支撑建筑物的外墙以及可能部分的 楼面和走廊的荷载。据说发现钢梁作为结构框架的一部分能支撑砌体墙(加上载人电梯的发 展)使今天的摩天大楼的建造成为可能。纵梁是桥面中平行于车道布置的梁,而横梁是很多 桥面中垂直于桥梁车道的较大的梁,被用来将纵梁上的板面荷载传递至支撑大梁或桁架。术 语大梁的采用是相当的不严格,但通常显示了一根较大的梁,或许是一根由较小的梁构成的 大梁。这些和其他类型的梁在下面的章节中进行讨论。 Sections Used as Beams The W shapes will normally prove to be the most economical beam sections(型钢梁) and they have largely replaced channels and S sections for beam usage. Channels are sometimes used for beams subjected to light loads, such as purlins(檩条), and in places where clearances available(可利用的净空)require narrow flanges. They have very little resistance to lateral forces and need to be braced. The W shapes have more steel concentrated in their flanges than do S beams and thus have larger moments of inertia and resisting moments for the same weights. They are relatively wide(较宽)and have appreciable lateral stiffness. (The small amount of space(范 围)devoted to (供..用)S beams in the LRFD Manual clearly shows how much their use has decreased from former years(前些年). They are today used primarily for special situation as where narrow flange widths are desirable, or where shearing forces are very high, or where the greater flanges thickness next to the web may be desirable where lateral bending occurs as perhaps with(就象)crane rails.) 梁的断面 W型钢通常证明是最经济的型钢梁,而且作为梁的使用,它们已经大量地代替了槽钢 和S型钢。槽钢有时用作支撑轻负荷的梁如檩条,以及用在可利用的净空需要狭窄翼缘的 位置处。它们对横向力几乎没有抵抗力,因此需要被支撑。W型钢的钢材比S型钢梁更多 的集中在它们的翼缘上,这样同样重量时就有较大的惯性矩和抵抗弯距。它们较宽,并有明 显的横向刚度。(在LRFD手册中供S型钢梁用的少量的范围清楚地显示了它们的使用从前 些年开始已经降低了多少。今天它们主要被用于特殊的情况如需要狭窄的翼缘宽度处,或者 剪力很大处,或者紧接着腹板处发生横向弯曲可能需要较大的翼缘厚度处,大概就象吊车轨 道。) Another common type of beam section is the open web joist(空腹搁栅)or bar joist(型钢搁栅). This type of section which is commonly used to support floor and roof slabs is actually a light shop-fabricated parallel chord truss(平行弦桁架). It is particularly economical for long spans and light loads. 另一个普通的梁截面的类型是空腹搁栅或型钢搁栅。这种通常用来支撑楼面板和屋面板的断 面类型实际上是一个轻质的工厂制造的平行弦桁架。它在大跨度和轻负荷时特别经济。 Unit 13 第十三单元 Survey 测量 教学目标 了解测量的内容、方法、范围和原理 了解常用的测量类型 熟悉各种测量方法和类型的词汇 熟悉科技类文献的常用句型 熟悉map、chart、plot、construction、draw的含义;so far、heretofore、by far的含义;have to do with、be referred to、be related to的含义;compatible with、pertain to 、application to 的 含义;;layout、staking out 的含义;construction的不同含义。 Surveying has to do with(与..有关)the determination of the relative spatial location(相对空间 位置)of points on or near the surface of the earth. It is the art(技术)of measuring horizontal and vertical distance between objects, of measuring angles between lines, of determining the direction of lines, and of establishing points by predetermined angular and linear measurements(角测量法 和线性测量法). 测量是关于确定地球表面上或接近地球表面的点的相对空间位置。它是测量物体之间水 平与垂直距离、测量线条之间夹角、确定线条方向以及通过预先确定角测量法和线性测量法 来建立点的技术。 Accompanying the actual measurement(度量)of survey are mathematical calculations. Distance, angles, directions, locations, elevations, areas, and volumes are thus determined from data of survey. Also, much of the information of the survey is portrayed graphically(图示描述)by the construction of maps, profiles(纵剖面图), cross sections(横剖面图), and diagrams(图表). 数学计算伴随着测量中的实际量度。根据测量数据就可确定距离、角度、方向、位置、 标高、面积以及体积。而且,测量中的很多信息是通过绘制地图、纵横剖面图和图表,以图 示形式被描述。 The equipment available and methods applicable for measurement and calculation have changed tremendously in the past decade. Aerial photogrammetry(航空摄影测量), satellite observation, remote sensing, inertial surveying(惯性测量), and electronic distance measurement(电子测距) laser techniques are examples of modern systems(现代方法)utilized to collect data usable in the surveying process. The relatively easy access to(利用)electronic computers of all size(各种容 量)facilitates the rigorous(精确的)processing and storage(处理和储存)of large volumes of data. 对测量和计算,可利用的设备和可应用的方法在过去十年中已经发生了惊人的变化。航 空摄影测量、人造卫星观测、遥感、惯性测量以及电子测距激光技术是现代方法中的例子, 被用来收集测量过程中可使用的数据。较容易地利用各种容量的电子计算机有助于精确地处 理和储存大量的数据。 With the development of these modern data acquisitions(收集)and processing systems, the duties of the surveyor have expanded beyond(超出)the traditional tasks of the field(现场)work of taking measurements and the office work of computing and drawing. Surveying is required not only for conventional construction engineering projects(项目), mapping, and property(地籍) surveys, but is also used increasingly by other physical sciences, such as geology(地质学)and geophysics(地球物理学); biology, including agriculture, forestry, grasslands(草原), and wildlife (野生动植物); hydrology(水文地理学)and oceanography(海洋学); and geography, including human and cultural resources(人文资源). 随着现代数据收集和处理系统的发展,测量员的职责已经超出了传统的现场进行测量和室内 进行计算和制图的任务。不仅一般的建筑工程项目、绘制地图、地籍测量需要测量,而且也 越来越多地用于其他的自然科学,如地质学和地球物理学;生物学,包括农业、林业、草原 和野生动植物;水文地理学和海洋学;以及地理学,包括人文资源。 The tasks in these physical science operations(活动)need to be redefined to include design of the surveying procedure(程序)and selection of equipment appropriate for the project; acquisition of data in the field or by way of remote station; reduction(整理)or analysis of data in the office or in the filed; storage of data in a form compatible with(适合于)feature retrieval(特征检索); preparation(整理)of maps or other displays in the graphical(绘图)(including photographic摄影) or numerical form needed for the purpose of survey; and setting of monument(界标)and boundaries in the field as well as control for construction layout(施工放样). Performance of these tasks requires a familiarity with the uses of surveying, knowledge of fundamentals of the surveying process(方法), and knowledge of various means by which data can be prepared for presentation. 这些自然科学活动的任务需要重新定义,包括设计测量程序和选择适合该项目的设备;在现 场或通过远距离的测站收集数据;在室内或现场整理或分析数据;以适合于特征检索的形式 储存数据;以测量所需的绘图(包括摄影)或数字形式整理地图或其他显示;在现场设置界 标和边界并控制施工放样。这些任务的实施需要熟悉测量的使用、测量方法的基本原理的知 识以及数据准备表达的不同方法的知识。 The earliest surveys known were for the purpose of establishing(确定)the boundaries of land, and such surveys are still important work of many surveyors. 最早了解的测量是用来确定土地的边界,这样的测量仍然是很多测量员的重要工作。 Every construction project of any magnitude(规模)is based to some degree upon measurements taken during the progress(发展)of a survey and is constructed about lines and points established by the surveyor. Aside from land surveys, practically all surveys of a private nature(私营性质) and most of those conducted by public agencies(公共机构)are of assistance in the conception(规划), design, and execution (施工)of engineering works. 在测量的发展过程中,任意规模的每个建筑项目在某种程度上都是根据所采用的测量方 法,然后绘制由测量员确定的线和点。除了土地测量外,实际上所有私营性质的测量和大多 数由公共机构经营的测量都对工程的规划、设计和施工有帮助。 For many years the government, and in some instances(在某些情况下)the individual states, have conducted surveys over large areas for a variety of purposes. The principal work so far(迄今为 止)accomplished consists of the fixing(确定)of national and state boundaries; the charting(绘 制)of coastlines(海岸线) and navigable(适于航行的)streams and lakes; the precise location(定位)of definite reference points(固定基准点)throughout the country; the collection of valuable facts(论据)concerning the earth’s magnetism(磁力) at widely scattered stations; establishment(建立)and observation of a greater network of gravity station(重力站)throughout the world; the establishment and operation(运转)of tidal and water level (潮位和水位)station; the extension(扩充)hydrographic(与水文地理学有关)and oceanographic(与海洋学有关) charting and mapping(绘制)into the approximately three-fourths of the world which is essentially(本来)unmapped; and the extension of topographic(地形的)mapping of the land(陆地) surfaces of the earth. 很多年来,政府以及在某些情况下各个州已经对大量的各种用途的区域进行了测量。迄今为 止,已经完成的主要工作包括确定了国家和州的边界线;绘出了海岸线和适于航行的河流和 湖泊;精确定位了遍及全国的固定基准点;收集了遍布各个分散测站的关于地球磁力的有价 值的论据;建立和观测了遍布世界的较大网络的重力站;建立和运转了潮位和水位站;扩充 绘制了本来未绘制的约3/4的世界范围内与水文地理学和海洋学有关的图表和地图;扩充绘 制了地球表面陆地的地形图。 Observations of a worldwide net of satellite triangulation stations(三角测量卫星观测站) were made during the decade 1964-1974. Results of the computations have been completed by 1985. They allow(有助于) determination of the shape of the earth from one to two orders of magnitude(数量级)better than has heretofore(迄今为止)been known. Consequently, surveys of global extent(全球范围)have been performed and will become common in the future. 在1964到1974年的十年间建立了全世界网络的三角测量的卫星观测站。到1985年已 经完成了计算结果。它们有助于更精确地确定地球的形状,其精度要比迄今为止所知的高出 一到两个数量级。因此,已经进行了全球范围的测量,这在将来成为平常事。 Thus surveys are divided into three classes: (a) those for the primary purpose of establishing the boundaries of land, (b) those providing information necessary for the construction of public or private works, and (c) those of large extent and high precision conducted by the government and to some extent by the states. There is no hard and fast line of demarcation(严格的界线)between surveys of one class and those of another(不同类型) regarding the methods employed, results obtained, or the use of the data of the survey. 因此,测量被分为三类:(a)主要用于确定土地边界的测量;(b)为公共或私人工程的 建造提供必要信息的测量;(c)由政府以及在某种程度上由州进行的大范围和高精度的测量。 不同类型的测量在采用的方法、取得的成果或测量数据的使用方面没有严格的界线。 Different types of surveying undertake(承担)the tasks of three classes. Geodetic surveying(大 地测量) is employed in the third class, which takes into account the true shape of the earth. Surveys making use of the principles of geodesy(测地学)are of high precision and generally extend(遍布)over large areas. Where the area involved is not great, as for a state, the required precision may be obtained by assuming that the earth is a perfect sphere(球体). Where the area is large, as for a country, the true spheroidal(椭球体)shape of the earth is considered. Surveys of the latter character have been conducted primarily through the agencies of governments. In the United States such surveys have been conducted principally by the U.S. National Geodetic Survey. Geodetic surveys have also been conducted by the Great Lake Survey, the Mississippi River Commission, several boundary commissions, and others. 不同类型的测量承担着这三类任务。大地测量被用于第三类的任务,它考虑了地球的实际形 状。利用测地学原理的测量具有很高的精度,且通常遍布很大的范围。对包含的范围不大如 一个州时,则可通过假定地球完全是个球体可以得到所需的精度。对范围较大如一个国家时, 则要考虑地球实际的椭球体形状。对后者特征的测量主要通过政府机构进行。在美国这样的 测量主要由美国国家大地测量局进行。大地测量也已由大湖勘测局、密西西比河委员会、一 些边界线委员会以及其他机构进行。 Though relatively few engineers and surveyors are employed full time in geodetic work(测量工 作), the data of the various geodetic surveys are of great importance in that they furnish(提供) precise points of reference to which the multitude of(大量)surveys of lower precision may be tied (连接). For each state, a system of plane coordinates(平面坐标系统)has been devised(建 立), to which all points in the state can be referred without an error of more than one part in 10 000 in distance or direction arising from the difference (差异)between the reference surface and the actual mean surface of the earth. 尽管较少的工程师和测量员专职从事测量工作,但是各种大地测量的数据很重要,它们 提供了精确的基准点,大量较低精度的测量可与其联测。每个州都已建立了一个平面坐标系 统,州内各点均可以参考这一坐标系统,基准面与实际的地球平均面之差所引起的距离或方 位的误差不会大于1/10000。 That type of surveying in which the mean surface of the earth is considered as a plane, or in which its spheroidal shape is neglected, is generally defined as plane surveying. With regard to horizontal distances and directions, a level line(水平线)is considered as mathematically straight, the direction of the plumb line(铅垂线)is considered to be same at all points within the limits of the survey, and angles are considered to be plane angles. By far(到目前为止)the greater number of all surveys are of(属于)this type. In general the surveys necessary for the works of human beings are plane survey. The shape of the earth must be taken into consideration only in surveys of precision covering(涉及)large areas. 认为地球的平均面是一个平面或忽略椭球体形状的测量通常定义为平面测量。关于水平距离 和方向,水平线在数学意义上被认为是直的,铅垂线的方向在测量限制范围内的所有点上被 认为是相同的,而角度被认为是平面角。到目前为止,大多数的测量都属于这种类型。通常 对人类工程必需的测量是平面测量。地球的形状只在涉及大范围的精确测量时才被考虑。 The operation(工作)of determining elevation is usually considered as a division(一部分)of plane surveying. Elevations are referred to(与..有关)a spheroidal surface, a tangent at any point in the surface being normal to(垂直于)the plumb line at that point. The curved surface of reference, usually mean sea level(平均海平面), is called a “datum” or curiously and incorrectly, a “datum plane”. The procedure ordinarily used in determining elevations automatically takes into account the curvature(曲率)of the earth, and elevation referred to the curved surface of reference are secured(获得)without extra effort on the part of the surveyor. In this procedure, the curvature of the earth’s surface can not be neglected even for very rough(粗略的)values of elevations. 确定标高的工作通常被认为是平面测量的一部分。标高和椭球体表面有关,该表面上任意一 点的切线垂直于该点的铅垂线。通常是平均海平面的参考曲面被称为“基准面”,或奇怪地、 不恰当地称为“基准平面”。通常用来确定标高的方法自动考虑了地球的曲率,而关于参考 曲面的标高,测量员没有额外的费力就可获得。在该方法中,地球表面的曲率不能被忽略, 即使对非常粗略的标高值。 Here a brief description of the various types of surveys will be given. Most of them employ plane rather than geodetic techniques. 这里将给出一个关于不同测量类型的简短描述。它们中多数采用平面技术而不是大地测 量技术。 Land surveys are the oldest type of survey and have been performed since earliest recorded history. They are plane surveys made for locating property lines(地籍线), subdividing land into smaller parts(分割土地), determining land areas and any other information involving the transfer of land from one owner to another(土地产权转移). These surveys are also called property surveys, boundary surveys, or cadastral surveys. 土地测量是最老的测量类型,自从最早有历史记载以来就已有之。它们属于平面测量方 法,用以定位地籍线、分割土地、确定土地面积以及其他包括土地产权转移在内的信息。这 些测量也称为地籍测量、边界测量或地产测量。 Topographic surveys(地形测量)are made for locating objects and measuring the relief(地貌), roughness(粗糙度), or three-dimensional variations of the earth’s surface. Detailed information is obtained pertaining to(关于)elevations as well as to the locations of man-made and natural features(人工和自然地物) (buildings, roads, streams, and so on) and the entire information is plotted on maps (called topographic maps). 地形测量用以定位物体以及测出地球表面的地貌、粗糙度或三向空间的变化。在得到了 关于人工和自然地物(建筑物、道路、河流等)的标高和位置的详细信息后,将全部的信息 绘在地图上(称为地形图)。 Route surveys(路线测量)involve the determination of the relief and the location of natural and artificial objects along a proposed(拟定的)route for a highway, railroad, canal, power line(输 电线), or other utility(应用). They may further involve the location or staking out(放样)of the facility and the calculation of earthwork quantities(土方工程量). 路线测量包括确定自然和人工的物体如公路、铁路、运河、输电线或其他应用沿着拟定 路线的地貌和位置。它们可进一步包括设施的定位或放样,并计算土方工程量。 City survey are made within a given municipality for the purpose of laying out(定位)streets, planning(布置)sewer systems(排水系统), preparing maps, and so on. When the term is used, it usually brings to mind(使人想起)topographic surveys in or near a city for the purpose of planning urban expansions or improvements. 城市测量是在一个特定的城市范围内用以定位街道、布置排水系统以及制作地图等。当 采用该术语时,它通常使人想起在一个城市中或城市边进行的地形测量,用以规划城市的扩 张和改进。 Construction surveys are made for purposes of locating structures and providing required elevation points during their construction. They are needed to control(指导)every type of construction project. 建筑测量用以确定建筑的位置,并在施工期间提供所需的标高点。它们被需要用来指导 每种建筑工程。 Hydrographic surveys(水文测量)pertain to(适合)lakes, streams, and other bodies of water(水域). Shore lines(海岸线)are charted, shapes of areas beneath water surface are determined, water flow(水流量) of streams is estimated, and other information needed relative to(相对于) navigation, flood control(防洪), development of water resources, and so on, is obtained. These surveys are usually made by a governmental agency. When hydrographic and topographic surveying are combined the resulting surveys are sometimes called cartographic survey(地图制图 测量). 水文测量适合于湖泊、河流以及其他水域。绘出海岸线、确定水面下区域的形状、估计 河流的水流量以及得到其他相对于航海、防洪、水资源发展等所需要的信息。这些测量通常 由政府机构进行。当水文测量与地形测量结合起来形成的测量有时称为地图制图测量。 Marine surveys(海洋测量)are related to hydrographic surveys but they are thought to cover a broader area. They include the surveying necessary for offshore platforms(近海平台), the science of navigation, theory of tides(潮汐学说)as well as the preparation of hydrographic maps and charts(海图). 海洋测量与水文测量有关,但被认为包含更广泛的区域。它们包括近海平台、航海科学、 潮汐学说以及制作水文图和海图所必需的测量。 Mine surveys(矿井测量)are made to obtain the relative positions and elevations of underground shafts(矿井), geological formations (地质组成), and so on and to determine quantities and establish lines and grades for work to be done. 矿井测量用以获得地下矿井的相对位置和标高、地质组成等,并确定将要进行的工作的 数量、路线和等级。 Forestry and geological surveys(林地和地质测量)are probably much more common than the average(一般的)layman realizes(了解). Foresters(林务员)use surveying for boundary locations, timber cruising, topography, etc. Similarly, surveying has much application in the preparation of geological maps(地质图). 林地和地质测量可能比一般的非专业人员所了解的普遍的多。林务员进行边界位置测 量、森林勘测测量、地形测量等。类似的,测量在制作地质图时有很多应用。 Photogrammetric surveys(摄影测量)are those in which photographs (generally aerial) are used in conjunction with(加上)limited(有限的)ground surveys (used to establish or locate certain control points visible from the air). Photogrammetry is extremely valuable because of the speed with which it can be applied, the economy, the application to(适用于)areas difficult to access(达 到), the great detail provided, etc. Its uses are becoming more extensive each year. 摄影测量是利用照片(通常是空中的)加上有限的地面测量进行的测量(用以确定从空 中能看见的某些控制点的位置)。摄影测量非常有价值,因为这种测量速度快、经济、适用 于难以到达的地区以及提供大量的详细资料等。它的使用一年比一年广泛。 In the decades to come there will undoubtedly be the other special types of surveying which will develop. Surveyors might very well(极有可能)have to establish boundaries under the ocean, in the Arctic and Antarctic, and even on the moon and other planets. Great skill and judgment by the surveying profession(测量业)will undoubtedly be required to handle these tasks. 在今后的几十年里,毫无疑问会有其他特殊类型的测量将逐步发展。测量员极有可能不 得不在海洋下、在北极和南极、甚至在月球和其他行星上确定边界。毫无疑问测量业将需要 很多的技能和判断来处理这些任务。 Unit 13 第十五单元 Soil Mechanics 土力学 教学目标 了解土的颗粒尺寸 熟悉土壤类型及其力学和物理性能的词汇 熟悉科技类文献的常用句型 熟悉frictional、cohesive的不同含义;drop、lower、sink、settle的不同含义。 Grain size(颗粒尺寸)is the basis of soil mechanics, since it is this which decides whether a soil is frictional(有摩阻力的)or cohesive(有粘结力的), a sand or a clay(粘土). Starting with the largest sizes, boulders(漂石)are larger than 10 cm, cobbles(卵石)are from 5 cm to 10 cm, gravel (砾石)or ballast(碎石)is from about 5 cm to 5 mm, grit(粗砂)is from about 5 mm to 2 mm, sand is from 2 mm to 0.06 mm. All these soils are frictional, being coarse(粗糙的)and thus non-cohesive. Their stability depends on their internal friction. For the cohesive or non-frictional soils the two main internationally accepted size limits(范围)are: silt(淤泥)from 0.02 mm to 0.002 mm, and clay for all finer material. There are, of course, many silty clays(粉质粘土)and clayey silts(粘质粉土). 土力学的基础是颗粒尺寸,因为是它决定了土壤是有摩阻力的还是有粘结力的,是砂还是粘 土。从最大的尺寸开始,漂石大于10cm,卵石在5cm到10 cm之间,砾石或碎石约在5cm 到5mm之间,粗砂约在5mm到2mm之间,砂在2mm到0.06mm 之间。所有这些土壤都 是有摩阻力的,是粗糙的,因而是没有粘结力的。它们的稳定性依赖于内摩擦力。对于有粘 结力或无摩擦力的土壤,国际上能接受的两个主要的尺寸范围是:淤泥在0.01mm到 0.002mm,而粘土为所有较细的材料。当然还有很多粉质粘土和粘质粉土。 Every large civil engineering job starts with a soil mechanics survey(地基勘测)in its early stage. The first visit on foot(踏勘)will show whether the site might be suitable, in other words, whether money should be spent on sending soil-sampling equipment out to it. The soil samples and the laboratory results obtained from the triaxial test, shear test and so on will show at what depth the soil is likely to be strong enough to take the required load. For a masonry or steel structure, this is where soil mechanics survey will end, having rarely cost more than 2 percent of the structure cost. 每一项大的土木工程任务在它的早期阶段是从地基勘测开始的。通过最初的踏勘显示该场地 是否适合,换句话说,是否应该花一定的费用运送土壤取样设备至现场。土壤样本以及根据 三向试验、剪切试验等所获得的实验室结果将显示在哪个深度上土壤可能足够坚固,能承受 所需的荷载。对砌体或钢结构来说,其地基勘察将到此结束,所需费用很少超过结构费用的 2%。 Generally, the strength of a soil increases with depth. But it can happen that it becomes weaker with depth. Therefore, in choosing the foundation pressure(地基压力)and level(深度)for this sort of soil, a knowledge of soil mechanics is essential, since this will give an idea of(对..有所了 解)the likely settlements. 通常,土的强度随深度而增加。但会发生强度随深度变弱的情况。因此,在选择这种土 的地基压力和深度时,土力学的知识是必要的,因为这将对可能的沉降有所了解。 There are, however, several other causes of settlement apart from consolidation(固结)due to load. These causes are incalculable(不可计算的)and must be carefully guarded against(预防). They include frost(霜冻)action, chemical change in the soil, underground erosion(侵蚀)by flowing water, reduction of the ground water level, nearby construction of tunnels(隧道)or vibrating machinery(机械)such as vehicles. 但是,除了荷载引起的固结外,还有其他一些沉降的原因。这些原因是不可计算的,必 须小心预防。它们包括霜冻作用、土壤中的化学变化、流水引起的地下侵蚀、地下水位的减 少、附近隧道的施工或者振动的机械如车辆。 Static load can cause elastic (temporary) or plastic (permanent) settlement, consolidation settlement being permanent. However, when plastic flow(塑性流)is mentioned in English, it generally means the failure of a soil by overload in shear. Consolidation settlement occurs mainly in clays or silts. 静荷载会引起弹性(暂时的)或塑性(永久的)的沉降,其中固结沉降是永久的。但是, 在英语中提到塑性流,它通常意味着超载引起土壤的剪切失效。固结沉降主要发生在粘土或 淤泥中。 From dynamic load alone the commonest settlements are found in sands or gravels, caused by traffic or other vibration, pile driving(打桩)or other earth shocks(冲击). A drop(降低) in the ground water level will often cause the soil to shrink and a rise may cause expansion(膨胀) of the soil. Ground water is lowered by the drainage(排水)which can be caused by any deep excavation(深开挖). The shrinkage which can occur with drying(干燥)is well shown by the clay underlying Mexico City, a volcanic ash. After seven weeks drying this clay shrinks to 6.4 percent of its initial volume. It is an unusual clay with the very high voids ratio(孔隙比)of 93.6 / 6.4 = 14.6. 在砂或砾石中发现了仅由动荷载如交通或其他振动,打桩或其他土地冲击引起的最普通的沉 降。地下水位的下降常常引起土壤的收缩,上升可能引起土壤的膨胀。由任何深开挖引起的 排水可导致地下水位的降低。干燥引起的收缩可通过墨西哥城下的粘土即火山灰来很好地说 明。在七个星期的干燥后,该粘土比它的初始体积收缩了6.4%。它是一种与众不同的粘土, 具有很高的孔隙比,为93.6/6.4=14.6。 Underground erosion is the removal of solids(固体颗粒的流失), usually fines(细颗粒), from the soil by the flow of underground water. The solids can be removed as solids(固态) or in solution(溶解状态), though only a few rocks are soluble enough(充分溶解)to be removed in this way. Rock salt(岩盐)is the commonest example of a soluble rock. Potassium salts(钾盐) also are soluble. 地下侵蚀是由于地下水的流动引起的固体颗粒通常是细颗粒从土壤中流失。固体颗粒能 在固态或溶解状态时流失,尽管只有一些岩石能以这种形式充分溶解后流失。岩盐是可溶解 的岩石中最普通的例子。钾盐也是可溶解的。 The permeability(渗透性)of a soil is important for calculations of underground flow(地下潜 流), for example of oil or water to a well, or of water into a trench(排水沟)dug for a foundation, or of water through an earth dam(土坝). Of the loose soils which can be dug with spade(铲), clays are the least permeable, silts slightly more(稍大), sands yet more(更大), and gravels even more. In other words, the permeability is in direct proportion to(与..成正比)the grain size of the soil. 土壤的渗透性对计算地下潜流是重要的,例如计算井中的石油或水,或计算为基础开挖 的排水沟中的水,或计算通过土坝的水。在可用铲开挖的疏松土壤中,粘土的渗透能力是最 小的,淤泥稍微大一些,砂更大一些,砾石甚至还要大。换句话说,渗透性与土壤的颗粒尺 寸成正比。 When a well is being pumped(抽水), the water flows towards(流向)it from every direction and the ground water surface (water table地下水位) around it sinks. As the distance from the well increases, the water table is lowered rather less, so that around the well it becomes shaped like a funnel(漏斗形), though it is usually called a cone of depression(降落锥体). 当井在抽水时,水从每个方向流向井中,在它周围的地下水表面(地下水位)便下沉。 随着离开井的距离的增加,地下水位降低得相当少,以致井的周围变成漏斗形,但它通常称 为降落锥体。 Unit 17 第十七单元 Tendering Procedure 招投标 教学目标 了解招投标过程 了解项目策略的确定与投标预审程序 熟悉招投标过程中的专业词汇 熟悉科技类文献中的常用句型 熟悉in accordance with、in connection with、in compliance with的不同含义;cover、comprise、 contain的含义;anticipated、intended、envisaged、prospective的用法;tender的不同含义。 This document presents(介绍)a systematic approach for tendering and awarding of contracts(签 订合同)for international construction projects. It is intended to assist the employer / engineer to receive sound competitive tenders(公开投标)in accordance with the tender(招标)documents so that they can be quickly and efficiently assessed. At the same time, an effort has been made to provide the opportunity and incentive(鼓励)to contractors to respond easily to invitations to tender for(投标)projects which they are qualified to implement. It is hoped that the adoption of this procedure will minimize tendering costs and ensure that all tenderers receive a fair and equal (公正与公平)opportunity to submit(提交)their offers(建议)on a reasonable and comparable(同等的)basis. Introduction 本文介绍了国际间的建筑工程的招投标和签订合同的系统方法。它用以帮助雇主/工程师收 到合理的、与招标文件一致的公开投标,从而对它们进行快速和有效地评估。同时,努力地 给予承包商机会和鼓励,使他们顺利地接受邀请而对他们有资格履行的工程进行投标。希望 采用这种方法将使招投标的费用最小,并确保所有的投标者在合理和同等的基础上能获得公 正与公平的机会来提交他们的建议。 介绍 Establishment of Procurement Method and Form of Tendering In the context(上下文)of this document the word “project’ covers all the stages from the initial idea to construct a given physical asset(有形资产)to the final taking-over(接收)by the employer of the completed work. 建立获取投标的方法和形式 在本篇的上下文中,“项目”一词包括了从最初建造一个特定 的有形资产的构思到最后雇主接收已完工程的全部阶段。 Project Strategy 项目策略 Projects may be organized and implemented in accordance with different strategies. Which strategy is best suited for the purpose depends on, for example, the nature and complexity of the project, the access to finance(融资渠道), life cycle(生命周期)costs of the projects, the technical and administrative capability of the employer and the general political and economic environment. 项目可以根据不同的策略进行组织和实施。何种策略最适合于项目的目标,依赖于如项 目的性质和复杂性、融资渠道、项目的生命周期费用、雇主的技术和管理能力以及总的政治 与经济环境。 The project strategy defines(规定)the way in which the project will be implemented, determines the role of each party involved and, where appropriate(适当处), specifies(指定)the way the project will operate. To a large degree contractual relationship(合同关系)between the parties and their individual rights, duties and risks are thereby also determined by the project strategy. 项目策略规定了项目实施的途径,确定了有关各方的任务,并在适当处指定了项目运作 的方法。因此,在很大程度上双方的合同关系以及各自的权利、义务和风险也由项目的策略 来确定。 At the implementation stage of a project, tendering serves as a method to ensure that the work is procured(获得)at competitive terms(条件). 在项目的执行阶段,投标作为一种确保在竞争的条件下获得该项工作的方法。 The choice of strategy is a major(较重要的)decision which has far-reaching consequences(深 远意义). Once a strategy has been settled it is of great importance that it be followed(遵循) throughout the implementation of the project. Lack of (没有)strict adherence(遵守)to the strategy may lead to flaws in the procurement process(获取过程), resulting in claims(索赔), disputes(争端)and extra cost for all concerned. 策略的选择是具有深远意义的较重要的决定。一旦定下策略,它即具有非常重要的意义, 应在整个项目的执行过程中被遵循。没有严格遵守该策略可能导致获取过程中的缺陷,导致 索赔、争端以及所有有关的额外费用。 Any part of a project which can be covered by a separate contract may in principle(通常) be made subject to(根据)tendering. 一份单独合同所包含的项目中的任何一部分通常都可以根据投标进行。 As soon as the project strategy has been decided, the employer, assisted by his engineer, should establish procurement methods and forms of tendering to be used in the project. 一旦确定项目策略,雇主应该在工程师的帮助下建立用于该项目的获取投标的方法和形 式。 The procurement methods and forms of tendering are established by determining: (1)The parts of the project for which tenders are to be sought(试图获得); (2)The conditions of contract to be adopted; (3)The award criteria; and (4)The tendering procedure. 通过确定下列内容来建立获取投标的方法和形式: (1)试图获得投标的项目部分; (2)采用的合同条件; (3)授予合同的标准; (4)投标过程。 Once these basic preconditions(前提)have been determined and agreed between the employer and his engineer, the planning of when and how the tendering can be carried out may commence. 一旦这些基本的前提被确定并在雇主和工程师之间协商一致,则何时和如何进行投标的 计划便可开始。 If, for unforeseen(无法预料的)reasons, changes in principle and form have to be made at a later stage in the project the implications(含意)of such changes have to be considered and assessed carefully. 由于无法预料的原因,如果在项目的后期不得不发生原则和形式上的变化,则必须小心 考虑并估计这些变化的含意。 Preparation of Programmes The tendering procedure, as described in this document, implies that certain activities have to be carried out in connection with(连同)each part of the project for which a separate tender is to be called(招标) . 计划的准备 正如本文所描述的,投标过程意味着某些活动必须连同项目的各个部分一起进 行,而该项目是进行单独招标的。 It is important that these activities are carried out in a systematic and timely(适时的)manner. They should therefore be planned carefully and incorporated in(并入)the programme for the project. 这些活动应该系统和适时地进行,这点很重要。因此,它们应该被仔细地计划,且并入 项目的计划中。 Normally, preliminary overall programme covering all major activities of the project is prepared in the initial stage of the project. As a minimum(作为最低要求), such programme should comprise the main phases of the project, that is: -Project definition -Tendering procedure -Design -Construction -Taking-over and should establish all milestones of significance in connection with(与..有关的)each phase. 通常在项目的初期准备好初步的、包括项目所有主要活动的总体计划。作为最低要求,该计 划应包含项目的主要阶段,即: —项目定义 —投标过程 —设计 —施工 —接管 并且应该设立与各个阶段有关的所有的重要的里程碑。 Calling tenders for a given part of the project should be carried out in compliance with(按照)the overall programme. 对特定项目部分的招标应该按照总体计划进行。 In order to ensure this compliance(一致性), detailed programmes should be made for implementing the tendering procedure for each part of the project. As a minimum, these programmes should specify duration(持续时间)and deadlines(最终期限)for the following activities in connection with each potential contract. -Preparation of tender documents -Preparation of prequalification(预审)document -Prequalification of tenderers -Obtaining tenders -Opening of tenders -Evaluation of tenders -Award of contract 为了确保一致性,应该对履行项目各个部分的投标过程作详细的计划。作为最低要求,这些 计划应该规定下列与各个潜在合同有关的活动的持续时间和最终期限。 —准备投标文件 —准备预审文件 —投标人的预审 —获得投标 —开标 —评标 —签定合同 Time should be allowed(留出)in each programme for the employer to make necessary decisions and give required approvals(批准). 在每一项计划中应该留给雇主一定的时间,以使他作出必要的决定,并给出所需的批准。 Further information about content and scope of each of these activities is given in the following section of this document. 关于每一项活动的内容和范围的进一步信息,在本文后面的章节中给出。 Prepration of Prequalification Documents General: Prequalification is recommended to ensure that tenders are sought only from contractors whom the employer / engineer has already established(确定)as having the requisite(必要的)resources and experience to perform the intended(预期)work satisfactorily. 预审文件的准备 一般:预审被建议用来确保投标只从那些雇主/工程师已经确定的、具有 必要的资源和经验从而能圆满地完成预期工作的承包商中去寻找。 Prequalification of Tenderers 投标人的资格预审 The aim of prequalification is to establish a list of capable(有可能的)firms whilst(同时)ensuring that a proper level of competition is safeguarded(维护). To achieve these objectives and to give added(更多的)encouragement for contractors to respond to invitations to tender(招标), no more than seven organizations should be prequalified unless the rules of the employer or financing institution otherwise dictate(另外规定). 预审的目的是为了确定有可能的公司名单,同时确保维护适当的竞争水平。为了达到这 些目的,并给予承包商更多的鼓励,使他们响应招标,预审应该不超过七个组织,除非雇主 或贷款机构的规则另有规定。 Prequalification Document Prequalification documents should give information about the project, the tendering procedure and the prequalification procedure. They should also specify what data is required from contractors wishing to prequalify. 预审文件 预审文件应该提供关于项目、投标过程和预审过程的信息。它们也应该规定来自 承包商的哪些数据是需要的,并希望预审。 The documents are prepared by the employer / engineer and will normally include the following: -Letter of invitation to prequalify -Information about the prequalification procedure -Project information -Prequalification application 该文件由雇主/工程师准备,且通常将包括下列内容: —预审的邀请信 —预审过程的信息 —项目信息 —预审申请 The documents should include inter alia(尤其)the following: -Name and address of the employer -Name and address of the engineer -Location of the project -Description(类型)of the project and scope of work included in the contract -Anticipated(预期的)programme, indicating the tender period(周期), contract award date, design/construction/ commissioning(试运转)periods and any other key dates -Conditions of contract to be used -Criteria for evaluation of tenders -Criteria for prequalification -Details(详细资料)of any work intended to be undertaken by nominated subcontractor(s)(指定分 包商) -Anticipated sources of finance (including any requirement for contractor financing筹措资金) -Payment arrangements envisaged(预期的) (including currencies) -Any financial guarantees to be given by contractors -Whether price escalation arrangements(涨价计划) will be included -Language and law of the contract -Any aspect of the intended work which is unusual and would(可能)thus have a bearing on (对..有影响)the contractors obligations(职责) -Charges for(收..费)purchase of tender documents, if applicable 该文件尤其应该包括下列内容: —雇主的姓名和地址 —工程师的姓名和地址 —项目的地点 —合同中包括的项目类型和工作范围 —预期的计划,指出投标的周期、合同签定日期、设计/ 施工/试运转周期以及其他关键的日期 —合同采用的条件 —评标标准 —预审标准 —打算由指定的分包商承担的工作的详细资料 —预期的财政来源(包括需要承包商筹措的资金) —预期的支付安排(包括货币) —承包商提供的财政保证 —是否包括涨价的计划 —合同语言和规则 —预期工作中与众不同的方面,因而可能会影响到承包商 的职责 —如果合适,对购买投标文件的收费 Applicants should also be advised of(告知): -The policy of the employer concerning domestic preference(国内 优惠) -The attitude of the employer to joint ventures(联合体). It is recommended that Joint ventures should be allowed to prequalify but that the subsequent formation of Joint ventures from amongst(从..中)prequalified organizations should be controlled as this reduces the breadth(范围)of competition. A prequalified organization should be allowed to strengthen its capability(实 力)by the subsequent incorporation, during the tender period, of non-prequalified firm(s), subject to the approval of the employer. -The number of copies of prequalification applications to be submitted. -The name, address and latest date(截止时间)for receipt of submissions (提交物), including any particular instructions for labeling(标注). -The language to be used for the submissions -The currency to be used for presenting(提供)financial information(报告). 申请者也应该被告知下列情况: —雇主有关国内的优惠政策 。 —雇主对联合体的态度。建议应该允许预审联合体, 但是随后从预审过的组织中形成的联合体应该加以 控制,因为这将缩小竞争的范围。应该允许预审过 的组织在投标期间,通过随后与未预审的公司的联 合来加强他们的实力,以易于获得雇主的认可。 —递交预审申请的复印件的数量。 —名称、地址、接受提交物的截止时间,包括特别标 注的说明。 —提交物所使用的语言。 —提供的财务报告所使用的货币。 Invitation to Prequalify The employer/engineer should publish a notice(发布通告) of inviting interested contractors to apply for prequalification documents, stating(声明)that tender(招标) documents will be issued only to(发给)a limited number(少数的)of companies/joint ventures selected by the employer/engineer as having the necessary qualifications(条件)to perform the work satisfactorily. 预审邀请 雇主/工程师应该发布通告邀请有兴趣的承包商来申请预审文件,声明招标文件 仅发给由雇主/工程师选择的、具备圆满完成该工作的必要条件的少数公司/联合体。 The notice should be published in appropriate newspapers and journals to give sufficient publicity (宣传)according to the particular circumstances of the project. The notice may also be issued to financing institution representatives, if relevant, and to government agencies responsible for foreign trade(外贸)so that the international community(团体)receives timely notification of the proposed project and instructions on how to apply. 根据该项目的特定环境,通告应发表在适当的报纸和杂志上以给予足够的宣传。如果有 关联,通告也可以发给贷款机构的代表,以及负责外贸的政府机构,使国际团体能及时地收 到被提议项目的通告和如何申请的说明。 The notice should be reasonably brief and where feasible contain: -Name of the employer. -Name of the engineer. -Location of the project. -Description of the project and scope of work. -Source of finance. -Anticipated programme (i.e. award of contract, completion and any other key dates). -Planned dates for issue of tender(招标)documents and submission of tenders(标书). -Instructions for applying for prequalification documents. -Date by(到..时为止)which applications(申请表)to prequalify must be submitted. -Minimum qualification requirements(限制条件)and any particular aspects which could be of concern(至关 重要)to prospective(预期的)tenderers. 通告应该适当地简短,可能包括: —雇主名称 —工程师名称 —项目地点 —项目类型与工作范围 —资金来源 —预期计划(即签定合同的日期、完工日期以及其它 的关键日期) —招标文件发布和标书递交的计划日期 —申请预审文件的说明。 —预审申请表必须递交的截止日期。 —最低的限制条件以及对预期的投标人至关重要的特 殊 情况。 Issue and Submission of Prequalification Documents On(一旦)receipt of requests from contractors, the employer/engineer should issue the prequalification document. 预审文件的发布与递交 一旦收到承包商的请求,雇主/工程师应该发给预审文件。 The letter of invitation to prequalify should state(说明)how the application is to be packaged and sent. 邀请预审的信件中应该说明 申请书 入党申请书下载入党申请书 下载入党申请书范文下载下载入党申请书民事再审申请书免费下载 将如何包装和送交。 The employer/engineer should acknowledge(确认)receipt of the completed prequalification applications from the contractors. 雇主/工程师应该对收到来自承包商的已完的预审申请书加以确认。 Analysis of Prequalification Applications The employer/engineer should evaluate the prequalification applications to identify(确定)those companies/joint ventures whom they consider to be suitably qualified(条件合适)and experienced to undertake the project. 预审申请书的分析 雇主/工程师应该对预审申请书进行评价,以确定被他们认为是条件合 适并有经验承担该项目的公司/联合体。 The evaluations should determine, for each company or joint venture: -Structure and organization. -Experience in both the type of work and the country or region in which it is to be undertaken. -Available resources, in terms of(在..方面) management capability, technical staff, construction and fabrication facilities, maintenance and training facilities, or other relevant factors. -Quality assurance procedures(措施)and environmental policy. -Extent to which any work would be likely to be subcontracted. -Financial stability and resources necessary to execute the project. -General suitability, taking into account any potential language difficulties. -Litigation(诉讼)or arbitration(仲裁)history. 对每个公司或联合体,评价时应该确定: —结构与组织 —对即将承担的工作类型以及工作所在的国家或地区 的经验 —在管理能力、技术人员、建造和安装设施、维修和 培训设施或其它相关的因素方面可利用的资源 —质量保证措施和环境政策 —有可能被分包的工作范围 —完成项目必须的财政稳定性和资金来源 —一般的适应性,考虑可能的语言困难 —诉讼或仲裁史 Selection of Tenderers If the resulting list, after those firms who were found unsuitable have been excluded, exceeds six potential tenderers and there are no special regulations or conditions imposed on(影响)the employer, the selection procedure should be continued to eliminate the less well-qualified(不太适合)in order to arrive at no more than six. 选择投标人 在那些被发现不适合的公司被排除以后,如果作为结果的名单超过了六个可能 的投标者,且没有影响雇主的特别规则或条件,则应该继续进行选择的过程来排除不太适合 的,以便获得不超过六个的投标者。 Notification of Applicants When the list of the selected tenderers has been prepared, successful applicants should be notified and requested to confirm(确认)their intention to submit a tender. This should ensure, as far as possible, an adequate number of competitive tenders. If a potential tenderer wishes to drop out(放弃)at this stage, the next best-placed should be invited and asked to confirm as above. Following this, all applicants should be notified of the list of selected tenderers without giving explanation for the decisions. 通知 关于发布提成方案的通知关于xx通知关于成立公司筹建组的通知关于红头文件的使用公开通知关于计发全勤奖的通知 申请者 当挑选的投标者的名单准备好时,应该通知成功的申请者,并要求确认他们递 交标书的意向。应该尽可能地确保有足够数量的竞争性投标。如果在这个阶段有潜在的投标 者想要放弃,则应该邀请下一个名次最列前的公司,并要求其确认上面所说的内容。接着将 挑选的投标者的名单通知所有的申请者,而对该决定不作解释。 Unit 18 第十八单元 Building Construction 建筑施工 教学目标 了解各类承包商和承包过程 了解承包过程中各方的关系 熟悉建筑施工中的专业词汇 熟悉科技类文献中的常用句型 熟悉be subject to 的不同含义;several 的不同含义;be engaged with、be engaged by的不同 含义;address、cite、argue的用法;Given..的用法;specification的不同含义。 The construction industry consists of numerous types of projects to include residential units, commercial institutions and industrial projects, and heavy and highway projects(市政项目). One means of classifying(分类)construction contractors is to identify(确定)the firms consistent with the type of work they perform; i.e., a residential contractor, a building or commercial contractor, or a heavy and highway contractor. 建筑业由很多类型的工程项目组成,包括住宅单元、商业机构和工业项目以及市政项目。 划分工程承包商类型的一种方法是确定该公司与他们所履行的工作类型是一致的;即住宅承 包商,建筑或商业承包商,或市政承包商。 Construction Contractors 工程承包商 (page 243) While(虽然)the purpose of this handbook addresses(针对..而写)the building/commercial contractor, it is helpful in understanding the characteristics of the building/commercial contractor, to contrast the characteristics of the firm to (将..与..形成对照)those of the residential and/or heavy and highway contractor. 虽然本手册的目的是针对建筑/商业承包商而写的,但它在理解建筑/商业承包商的特征 时,有助于将公司的特征与住宅承包商和/或市政承包商的特征形成对照。 As pointed out there is the advantage of less sensitivity to the economy for the firm that has skills and performs each of the three types of work. On the other hand, it is not possible for every firm to involve itself in(陷于)the three types of construction work in that(因为)the physical (自然 科学的)and management skills required differ for the three types of work. Obviously, not every firm can or should strive(努力)to possess all the skills required to enable its performing each of the three types of work. 正如所指出的,有着一定技术、并履行这三种工作的公司具有对经济不太敏感的优势。 另一方面,每个公司不可能将其自身陷于三种施工工作,因为三种工作所需的自然科学和管 理技术是不同的。显而易见,不是每一个公司都能够或应该努力拥有所有所需的技术,使其 能够履行三种工作。 Residential Contractor The decision to specialize in(专攻)residential, commercial, or heavy and highway construction should recognize the unique characteristics of each of the three types of work. Residential construction is characterized by(表现为..的特征)severe cycles in volume(数 量). The residential contractor is subject to(受..的支配)the policies of the government. Due in major part to changes in the government’s fiscal and monetary policies(财政和货币政策), new residential housing(住宅建设)starts may approach(接近)two million units one year and one million the next. Variations in starts from one year to the next and from one season to the next often create unique management problems for the residential contractor. His available cash(可用 现金)through stack volume(堆积,可引申为建设)periods can make the difference(区别对 待)between a continuing firm and a bankrupt firm. 住宅承包商 决定专攻住宅建设、商业建设还是市政建设时,应该承认这三种工作各自独特 的特性。住宅建设表现为数量上严重循环的特征。住宅承包商受政府政策的支配。主要由于 政府财政和货币政策的变化,新的住宅建设的启动可能这一年接近两百万套,下一年一百万 套。启动时,从这一年到下一年、从这一季到下一季的变化常常引起住宅承包商独特的管理 问题。在整个建设期间,他的可用现金允许在继续运作的公司和破产的公司之间区别对待。 Residential contractors have the advantages of being able to operate on a low volume in that they normally have relatively low overhead(企业管理费用) versus the building or heavy and highway contractors. Whereas the building or heavy and highway contractor must compete against above average-sized contractors, each having relatively sound(合理的)management practices(经 验), the residential contractor compete against much smaller firms who normally have less sophisticated(完善)management skills. This is not to say that the residential contractor does not have competition, the opposite is in fact true. However, the size of the average competitor and the management skills of the average competitor allow the residential contractor to actually operate out of his house(脱离其机构)as a one-man show(独角戏). Because of this, the number of residential contractors is numerous, often leading to excessive competition, low profit margins(利 润率), and bankruptcies. 住宅承包商具有能够少量运作的优势,因为他们相对于建筑承包商或市政承包商来说,具有 相对低的企业管理费用。住宅承包商与小得多的公司竞争,那些小公司通常有着不太完善的 管理技术,而建筑承包商或市政承包商必须与超出一般规模的承包商竞争,那些承包商都具 有相对合理的管理经验。这不是说住宅承包商没有竞争,事实上正好相反。但是,一般竞争 者的规模和管理技术实际上允许住宅承包商脱离其机构独自运作。因此,住宅承包商的数量 众多,常常引起过多的竞争、低的利润率以及破产。 Heavy and Highway Contractor Several differences exist between the building contractor and the heavy and highway contractor. For one, the building contractor is normally less dependent on the need for expensive equipment than is the heavy and highway contractor. Because of its high investment in equipment, the main management task for the heavy and highway contractor centers on(集中)the ability to effectively utilize equipment and to minimize idle equipment(闲置设备) time. On the other hand, the building contractor is more dependent on the use of labor. Its management needs center on effective personnel management(人事管理)and the ability to control the many materials that flow to the commercial building construction project. 市政承包商 在建筑承包商和市政承包商之间存在一些区别。一方面是建筑承包商通常比市 政承包商更少依赖于昂贵设备的需要。由于对设备的高额投资,市政承包商的主要管理任务 集中在能够有效地利用设备,并使闲置设备的时间最小。另一方面,建筑承包商更依赖于劳 动力的使用。其管理要求集中在有效的人事管理以及能够控制流向商业建筑施工项目的大量 材料。 The heavy and highway contracting firm tends to be less subject to(遭受)bankruptcy than the residential contractor or the commercial building contractor. Perhaps this is due in part(部分地) to the fact that heavy and highway work (sometimes categorized as(归类为)public-works construction) tends to be more stable as to profit margin earned. In additional, because of the high equipment investment needed to operate, the heavy and highway contractor tends to be a large firm with a relatively sound financial structure(财务结构). Several of these differences in the types of firms are summarized in Fig. 18-2 and 18-3. 市政承包公司往往比住宅承包商或商业建筑承包商更少遭受破产。这可能部分是由于市 政工程(有时归类为公共工程建设)往往在赚取的利润率上更稳定。而且,由于需要高额的 设备投资进行运作,市政承包商往往是一个大型的公司,具有相对合理的财务结构。不同类 型公司中的这些区别总结在图18-2和图18-3中。 General v. Subcontractor Within the classifications of residential, building, and heavy and highway contractors is a class of(一类)contractors referred to as specialty contractors or subcontractors. These types of firms continue to be founded by craftsmen(工匠)and highly skilled(非常熟练的)individuals(个体). Typically(一般), the subcontractors are small as to the number of employees and its volume of work. Subcontractors normally have relatively low overhead but are highly dependent on labor and labor productivity. Competition tends to be high and profit margins vary depending on the type of speciality work performed. Unlike the general contractor, the subcontractor is normally responsible for his own work. As such(同样地)the management skills needed to coordinate(协调)the skills of several(不同的)labor crafts(工 艺)or flows(流通)of several types of materials are not vital to the subcontractor’s profit on a project or its financial stability. What is needed is an ability to perform a highly skilled type of work and to be able to obtain high productivity while carrying out the work. 总承包商与分包商 在住宅承包商、建筑承包商和市政承包商的分类范围中,有一类承包商 称为专业承包商或分包商。这类公司不断地由工匠和非常熟练的个体创办。分包商在雇员数 量和工作量方面一般是小规模的。分包商通常具有相对低的企业管理费用,但是高度依赖于 劳动力和劳动生产力。竞争往往是激烈的,利润率随进行的专业工作的类型而变化。不象总 承包商,分包商通常只负责其自己的工作。同样地,为协调不同劳动工艺的技能或不同种类 的材料的流通所需的管理技能对分包商的项目利润或其财务稳定性不是至关重要的。分包商 所需要的是能够非常熟练地履行某类工作以及在进行该项工作时能够获得高的生产力。 The building or commercial contractor is normally engaged as a prime contractor(总承包商) directly with (打交道)the project owner. The contractor has responsibility for delivering the completed construction project to (移交)the project owner. In effect (实际上)the contract it signs(签署)places the firm in a role of independent contractor. In this process, specialty contractors are typically engaged(雇佣)by the contractors serving as subcontractors. The General Contracting Process 总承包过程 The General Contracting Process 总承包过程 (page 249) The building or commercial contractor serving(适合于)the role outlined above is referred to as the general contractor for the project. The process itself is commonly referred to as the general contracting process. The process is illustrated in Fig. 18-4. 适合于上面所描述的角色的建筑或商业承包商称为项目总承包商。该过程本身通常称为 总承包过程。该过程如图18-4所示。 The majority of building construction contracts are let(签定)using the general contracting process (note: the next chapter addresses(提出)an alternative process). Advocates(提倡者)of the general contracting process point to several reasons for their preference for the general contracting process. Project owners cite(列举)the fact that by means of soliciting bids(招标)on one single contract for their entire project via(通过)the single general contract, they are able to secure the most competitive (i.e., lowest) price for the proposed project. Some project owners also argue(指出) that another advantage of this process is the fact that they, as the project owner, only have to deal with(与..打交道)a single contractor instead of having to contract and deal with individual specialty contractors. 大多数建筑施工合同采用总承包的方法被签定(注意,下一章节提出另一种可选择的方法)。 总承包方法的提倡者对他们偏爱该方法指出了几个理由。项目的业主列举了这样一个事实, 即通过采用单独总承包的方式对他们整个项目进行单独承包的招标,他们能获得被提议项目 最有竞争性(即最低)的价格。一些项目业主也指出该方法的另一个优势,即作为业主,他 们只须与单个承包商打交道而不必与各个专业承包商签定合同并打交道。 The general contractor himself may favor(偏爱)the process relative to another process (e.g., construction management) in that the potential for substantial(很多)profits exists if the contractor performs efficiently. The general contract typically signs a lump-sum contract(总价合同)for its services. If the firm is able to construct the project for less than the contract amount(承包价), the entire difference(差额)becomes profit for the firm. Naturally, the competitive bidding(竞标) process limits the amount of profit that a firm can realize. However, given the documentation that as much as 50% of all on-site time is non-productive, the potential for that profits associated with eliminating or even reducing this non-productive time is substantial. It is this potential profit that the general contractor seeks. In effect the general contractor takes on(承受)a lump-sum contract risk as a means of seeking a large profit. Naturally it also follows(必然是)that while having a potential for a significant profit on a job, the possibility of a significant dollar(财富)loss also exists. 相对于另一个方法(比如施工管理),总承包商自身可能偏爱该方法(总承包),因为如果承 包商有效地完成任务,就会有很多潜在利润。总承包对它的服务一般签署总价合同。如果公 司能以少于承包价建造该项目,全部的差价就成为公司的利润。自然,竞标过程限制了公司 能实现的利润值。但是,据文献记载多达一半的现场时间是无生产效益的,则消除或甚至减 少该无生产效益的时间带来的潜在利润是很大的。这正是总承包商寻求的潜在利润。实际上, 总承包商以承受总价合同的风险作为寻求巨大利润的方法。自然,当一项工作具有巨大的潜 在利润时,它也必然存在巨大财富损失的可能。 The architect/engineer designer illustrated as part of the project team in Fig. 18-4 may also argue(表明)in favor of the general contracting process. In particular the architect/engineer designer may cite the benefit of only having to write contract documents for a single contractor rather than write contract documents for a series of multiple specialty contracts. In addition most designers would likely favor administering a single construction contract rather than multiple contracts. 如图18-4 中所示的建筑师/工程师设计人员,其作为项目组的一部分可能也表明喜欢总承包 的方法。特别是建筑师/工程师设计人员可能列举了只须为单个承包商而不是一系列的多个 专业合同书写合同文件的好处。而且,多数设计师可能喜欢管理单个施工合同而不是多个合 同。 Independent of(与..无关)the project owner, the designer, or the general contractor, an independent party(独立方)might argue(认为)that the general contracting process enhances efficiency, technological change(科技进步)and free trade. Each and every bidder(投标人)in the general-contracting process has an equal opportunity to be low(低价)bidder for the owner’ s project. Given the competitive bidding process, it can be argued(表明)that the contractor will seek out efficient means of performing construction methods to include seeking new technology and cost-control means. Given this fact, it follows that the general contracting process promotes a more cost-effective construction industry(建筑业). 与项目业主、设计师或总承包商无关的某一独立方可能认为总承包方法提高了效率、增进了 科技进步和自由贸易。在总承包方法中每个投标人具有同等的机会成为业主项目的低价投标 人。通过竞标过程可以表明,承包商将寻找有效的方法进行施工,包括寻求新的技术和费用 控制的方法。鉴于这个事实,则总承包方法必然促进了一个成本更有效的建筑业。 As an alternative(另一选择)to the competitive bidding procedure, the potential owner or his architect/engineer may negotiate with(与..协商)a contractor for building the project. This contractor is usually chosen because of his skill, his reasonable price, and his dependability(可靠 性). In order to assure himself of work in a negotiated contract environment, the construction contractor must maintain a respectable reputation(不错的信誉)with potential construction project owners. 作为竞标方式的另一种选择,可能的业主或他的建筑师/工程师可以与承包商协商来建 造该项目。该承包商通常由于其技能、合理的价格以及可靠性而被选择。为了确保其自身在 一个议标合同的环境下工作,工程承包商必须同可能的工程项目的业主保持不错的信誉。 Negotiated Contracts 议标合同 (page 252) Negotiated contracts often have the advantage of producing better coordination(配合)between the owner, the architect/engineer, and the contractor. This improved(改进的)coordination often results in less construction delay time, better project quality, and savings in money for the owner. 议标合同常常具有在业主、建筑师/工程师和承包商之间形成较好配合的优势。改进的 配合常常导致较少的施工拖延时间、较高的项目质量以及业主资金的节约。 By using a negotiated contract, construction on a project may actually start before the completion of the plans(设计)and specifications(合同条款). In this case, the owner signs a letter of intent (意向书)with the contractor. This letter of intent assures the contractor that he will be paid for his services, even though the final contract for the project has not been signed, owing to the lack of(没有)the finalization(最后决定)of the plans and specifications. The contractor is paid for his costs plus a negotiated fixed fee or percentage of the project’s costs. 通过采用议标合同,项目的施工实际上可以在设计和合同条款完成之前开始。在这种情 况下,业主与承包商签署一份意向书。该意向书确保承包商将对他的服务获得支付,即使由 于没有最后定下设计和合同条款,项目的最后合同还未签定。承包商获得其付出的成本加上 一个协商的固定费用或项目成本的某个百分比。 Arguments(观点)against negotiated contracts include higher contract prices and a lack of contractor incentive(鼓励)in finding new construction methods to do the job for a lower cost. The argument of higher owner project cost is debatable(有争议的); i.e., competitive contract owner costs must include advertising and lettering(发信函)cost. In addition, the owner is more apt to (易于)get an irresponsible(不可靠的)contractor in a competitive bidding procedure versus a negotiated contract procedure. Negotiated contracts are gaining popularity(普及)in the construction industry. However, the competitive bidding procedure remains the rule(统治)in awarding construction contracts. 反对议标合同的观点包括较高的合同价格,并缺乏鼓励承包商寻找新的施工方法从而以较低 的费用进行工作。业主较高的项目费用的观点是有争议的;即业主竞争性合同的费用必须包 括登广告和发信函的费用。而且,竞标方式相对于议标合同方式,业主更易于获得不可靠的 承包商。议标合同在建筑业获得了普及。但是,在签定施工合同时竞标方式依然处于统治地 位。 A single contractor will seldom construct an entire project for the project owner. This might only occur on a small project, such as a home owner hiring a contractor to pour a driveway(车道). In this book, the construction project is meant to imply a somewhat large project; i.e., several(一些) trades(交易)or skills are required for the building of the project. Projects such as home building, industrial construction, highway construction, and dams require several(不同的)types of contracting skills. Owing in part to the restricted size(有限的规模)of contracting firms and the unfeasibility of overexpanding (过分扩张的不可能性), the average construction contractor is usually restricted to a few skills or types of work which he can perform. As a result, projects which require several(各种)different types of labor trades(手艺)or skills will have several contractors. Contractor Responsibility to Owner 承包商对业主的职责 单个承包商很少建造项目业主全部的工程。这只可能发生在小项目,如住宅业主雇佣一个承 包商浇灌一条车道。在本篇中,建筑项目意味着一个稍大的项目;即项目的建造需要一些交 易或技能。诸如住宅建设、工业建设、公路建设以及水坝的项目需要不同类型的承包技能。 部分是由于承包公司有限的规模以及不可能过分扩张,一般的 工程承包商通常被限制于其 能履行的一些技术或工作类型上。因此,需要各种不同类型的劳动手艺或技能的项目必须有 不同的承包商。 In a normal contract, the owner will select a general contractor (either by a competitive bidding procedure or by negotiation). This general contractor will usually perform some of the actual project construction, but not all of it. Some states(规定)require that on their public construction projects, the general contractor perform, at least, a defined percentage (规定的比例)of the actual construction. This is done with the intent of facilitating better overall project coordination between the project’s contractors. In the normal contract, the general contractor is given the responsibility of the entire project. On the other hand, the owner can hire a so-called(通常所说的)construction manager(工程项目经理)who recommends a need and a design, supervise the overall project (including financing), and coordinates the project’s contractors. Such an arrangement is referred to as a management contract or as construction management. 在一般的合同中,业主会选择一个总承包商(通过竞标方式或商议)。总承包商通常会履行 实际项目施工的一部分,但不是全部。有些规定要求对公共建设项目,总承包商至少应履行 实际建设的规定比例。这样做是为了更好地促进整个项目在项目承包商之间的配合。在一般 的合同中,总承包商对整个项目负责。另一方面,业主可以雇佣通常所说的工程项目经理, 他会建议某个需要和某个设计,监督整个项目(包括筹措资金),并配合项目的承包商。这 样的安排称为管理合同或施工管理。 In the general contracting process, the project designer and general contractor each typically sign contracts directly with the project owner. However, whereas the designer contract with the project owner is typically an agency contract, the general contractor is engaged by the project owner via all independent contractor agreement(协议). 在总承包过程中,项目设计师和总承包商一般各自直接与项目的业主签定合同。但是, 总承包商通过所有独立的承包商协议而受项目业主的雇佣,而设计师与项目业主的合同一般 是代理合同。 Designer – General Contractor Relationship 设计师与总承包商的关系 In the general contracting process set out(展示)in Fig. 18-4, the general contractor and the project designer have no direct contract relationship. However, given the fact that the designer serves as the project owner’s agent, one might argue(认为)that the designer has the contract rights of the project owner and thus has an indirect contract relationship with the general contractor. 在图18-4中所展示的总承包过程中,总承包商与项目设计师没有直接的合同关系。但 是鉴于设计师作为项目业主的代理人,可以认为设计师拥有项目业主的合同权,这样与总承 包商有着间接的合同关系。 In actuality the designer does not direct(指导)the actions of the general contractor and vice versa(反之亦然). In fact, the designer typically goes out of its way(特意)not to direct the general contractor because the designer does not want to take on the liability(责任)for the general contractor’s actions or performance. For example, the designer’s on-site project representative does not attempt to advise the general contractor’s subcontractors directly or(否则)the designer may subsequently be subject to legal damages(法律赔偿金). 实际上,设计师不指导总承包商的活动,反之亦然。事实上,设计师一般不特意指导总 承包商,因为设计师不想对总承包商的活动或行动承担责任。例如,设计师的现场项目代表 不会试图直接建议总承包商的分包商,否则设计师可能随后易遭受法律赔偿金。 While(尽管)the project designer does no “direct” the general contractor, the designer does have project administration-contract duties. In particular, the architect/engineer designer must “observe” the put-in-place(恰当的)construction of the contractor to determine that the work is compatible with the contract specifications. The designer must also aid the general contractor in the interpretation of the contract documents to include the drawings and specifications(说明). It is also the designer’s duty to pass judgment on (评定)the amount of work completed by the contractor and to approve(核准)owner progress payments(分期付款)to the contractor. 尽管项目设计师不“指导”总承包商,但设计师确实具有项目管理合同的职责。特别是,建 筑师/工程师设计人员必须“观察”承包商恰当的施工,以确定该项工作与合同条款的一致 性。设计师也必须帮助总承包商解释合同文件,包括图纸和说明。评定承包商已完的工作量 和核准业主对承包商的分期付款也是设计师的职责。 Given this somewhat “policing” role(管制角色)of the project designer in regard to the general contractor, on occasion(有时)there has been somewhat of an adverse(敌对)relationship between the designer and general contractor. This potential adverse relationship aids neither the project owner, the designer, nor the contractor. A spirit of cooperation is necessary between all these entities(实体)in the general contracting process to enable a project to be built on a time-and-cost budget and to satisfy the quality standards set out(列出) in the specifications. 鉴于项目设计师对于总承包商有点“管制”的角色,设计师与承包商之间有时有一些敌 对的关系。这种潜在的敌对关系既无助于项目业主、设计师,也无助于承包商。在总承包过 程中所有的实体之间的合作精神是必须的,使项目能在预算的时间和费用下被建造,并且满 足合同条款中列出的质量标准。 Whether the owner of a project is an individual, a company, or a government agency, the owner is responsible for the definition(解释)of the project and establishment of the budget to finance it. Upon becoming interested in a potential project, the owner usually employs an architect to plan(规划)overall designs; others require an engineer to determine the most economical and safe design. In addition, many projects require the services of both an architect and an engineer. Projects designed solely(完全地)by architects are referred to as building construction(建筑构 造)projects, whereas products designed solely by engineers are referred to as engineering construction(工程建设)projects. From this point on, the individual or company the owner hires to design his project will be referred to as the architect/engineer. Owner – Architect/Engineer Relationship 业主-建筑师/工程师的关系 无论项目的业主是个人、公司还是政府机构,业主负责解释项目和确定预算以筹集资金。一 旦对某一潜在的项目感兴趣,业主通常雇佣一位建筑师规划整个设计;其余的需要一位工程 师来确定最经济和最安全的设计。而且,很多项目需要建筑师和工程师两方的服务。完全由 建筑师设计的项目称为建筑构造项目,而完全由工程师设计的成果称为工程建设项目。从这 点上看,业主雇佣的、为其设计项目的个体或公司将称为建筑师/工程师。 The architect/engineer is responsible for the drawings and specifications for the owner’s projects and for supervision of construction of the project. The owner usually pays the architect/engineer on an hourly basis, a fee as a percentage of the total cost, or on a fixed fee basis. The architect/engineer is most commonly(常见)chosen through negotiation rather than through a competitive bidding process. Some large projects do have a competitive bidding procedure to determine the architect/engineer. However, it is much more common for a potential project owner to seek out(找到)an architect/engineer on the basis of his past performances(业绩). The reputation of an architect/engineer is an extremely important attribute(品质)when he is seeking work with(与..合作)potential project owners. 建筑师/工程师负责业主项目的图纸和说明,以及负责监督项目的施工。业主通常给建筑师/ 工程师的工资以每小时、总费用的一个百分比费用或固定的费用来支付。选择建筑师/工程 师最常见的是通过协商而不是通过竞标过程。一些大型的项目确实通过竞标过程来确定建筑 师/工程师。但是,对潜在的项目业主,更常见的是根据其过去的业绩找到建筑师/工程师。 当建筑师/工程师在寻找与潜在的项目业主一起合作时,其信誉是一项非常重要的品质。 Although in most cases the construction project owner, the architect/engineer, and the contractor are three separate(独立)individuals or firms, some projects will have the architect/engineer internal to(属于)the owner’s company or organization. Many large corporation(公司)(e.g., Procter and Gamble宝洁) design and supervise their own construction projects. In such instances, the owner and architect/engineer become one and the same(同一个)individual or company. 虽然工程项目的业主,建筑师/工程师,以及承包商在绝大多数情况下是三个独立的个 体或公司,但是某些项目的建筑师/工程师属于业主的公司或机构的。许多大型公司(如宝 洁)自己设计并监督他们的工程项目。在这种情形下,业主和建筑师/工程师成为同一个个 体或公司。 作业练习 通过一篇Reading Material的学习,进一步了解工程管理(CM)中所涉及的内容。
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