土木工程楼房外文翻译

土木工程楼房外文翻译 英 文 翻 译 一 建筑结构资料原文: Footings Types and function of substructure, or foundation, is that part of a structure which is usually placed below the surface of the ground and which transmits the load to the underlying soil or rock. All soils compress noticeably when loaded and cause the supported structure to settle. The two essential requirements in the design of foundations are that the total settlement of the structure shall be limited to a tolerably small amount and that differential settlement of the various parts of the structure shall be eliminated as nearly as possible. With respect to possible structural damage, the elimination of differential settlement, i.e., different amounts of settlement within the same structure, is even more important than limitations on uniform overall settlement. To limit settlement as indicated, it is necessary to transmit the load of the structure to a soil stratum of sufficient strength and to spread the load cover a sufficiently large area of that stratum to minimize bearing pressure. If adequate soil is not found immediately below the structure, it becomes necessary to use deep foundations such as piles or caissons to transmit the load to deeper, firmer layers. If satisfactory soil directly underlies the structure, it is merely necessary to spread the load, by footings or other means. Such substructures are known as spread foundations, and it is mainly this type which will be discussed. Types of spread foundations Footings generally can be classified as wall and column footings. The horizontal outlines of the most common types are given. A wall footing is simply a strip of reinforced concrete, wider than the wall, which distributes pressure. single column footing are usually square, sometimes rectangular, and represent the simplest and most economical type. Their use under exterior columns meets with difficulties if property rights prevent the use of footing projecting beyond the exterior walls. In this case combined footings or strap footings are used enable one to design a footing which will not project beyond the wall column. Combined footings under closely spaced, heavily loaded interior columns where single footings, if they were provided, would completely or nearly merge. 1 Such individual or combined column footings are the most frequently used types of spread foundations on soils of reasonable bearing capacity. If the soil is weak and/or column loads are great, the required footing area become so large as to be uneconomical. In this case, unless a deep foundation is called for by soil conditions, a mat or raft foundation is resorted to. This consists of a solid reinforced-concrete slab which extend under the entire building and which consequently distributes the load of the structure over the maximum available area. Such a foundation, in view of its own rigidity, also minimizes differential settlement. it consists, in its simplest form, of a concrete slab reinforced in both directions. A form which provides more rigidity and at the same time is often more economical consists of an inverted beam-and girder floor. Girders are located in the column lines in one direction, which beams in the other, mostly at closer intervals. If the columns are arranged in a square pattern, girders are equally spaced in both directions and the slab is provided with two ways reinforcement. Inverted flat slab, with capitals at the bottoms of the columns, are also used for mat foundation. Factors affecting the design of concrete footings In ordinary constructions the load on a wall or column is transmitted vertically to the footing, which in turn is supported by the upward pressure of the soil on which it rests. If the load is symmetrical with respect to the bearing area, the bearing pressure is assumed to the uniformly distributed. It is known that this is only approximately true. Under footing resting on coarse-grained soils the pressure is larger the center of the footings and decrease toward the perimeter. This is so because the individual grains in such soils are somewhat mobile, so that the soil located close to the perimeter can shift very slightly outward in the direction of lower soil stresses. In contrast, in clay soils pressures are higher near the edge than at the center of the footing, since in such soils the load produces a shear resistance around the perimeter which adds to the upward pressure. It is customary to disregard these nonuniformities because their numerical amount is uncertain and highly variable, depending on type of soil, and because their influence on the magnitudes of bending moments and shearing forces in the footing is relatively small. On compressible soils footings should be loaded concentrically to avoid tilting, which will result if bearing pressures are significantly larger under one side of the footing than under the opposite side. This means that single footings should be placed concentrically under the columns and wall footing concentrically under the walls and 2 that for combine footings the controlled of the footings area should coincide with the resultant of the column loads. Eccentrically loaded footings can be used on highly compacted soils and on rock. It follow that one should count on rotational restraint of the column by a single footing only when such favorable soil conditions are present and when the footing is designed both for the column load and the restraining moment. Even then, less than full fixity should be assumed, except for footings on rock. The accurate determination of stresses, particularly in single-column footings, is not practical, since they represent relatively massive blocks which cantilever from the column in all four directions. Under uniform upward present they deform in a bowl shape, a fact which would greatly complicate an accurate stress analysis. For this reason present procedures for the design of such footings are based almost entirely on the results of two extensive experimental investigations, both carried out at the university of Illinois. These tests have been reevaluated, particularly in the light of newer concepts of strength in shear and diagonal tension. Multi—story buildings Structural framing. The l framing of a multi-story building is a system of beams, girders or trusses , and columns, designed to carry all the gravity loads of the structure and to resist wind and earthquake forces. The roof and the floor systems are directly supported by horizontal beams and girders spanning the distance between the vertical columns. The details of a typical tier or floor level usually can be duplicated and extended both horizontally to cover a wide area and vertically to skyscraper heights, except when high wind loads or earthquake loads require a modification in the framing scheme. In planning the structural framing, early attention should be given to provisions for special facilitates such a elevator shafts and stairwells. These components extend through several stories. Suggesting the fixed position of some of the columns. The rest of the columns maybe arranged in a regular pattern from a consideration of the architectural layout and the typical construction used for the roof , floor , walls , and partitions. The AISC specification allows three types of construction in steel frames based on the type and behavior of the connections. Type 1, commonly designated as ―rigid—frame‖(continuous frame), assumes that bean—to—column connections have sufficient rigidity to hold virtually unchanged the original angles between intersecting members. Type 2, commonly designated as ―simple‖ framing 3 (unrestrained,free-ended), assumes that, in so far as gravity loading is concerned, the ends of beams and girders are connected for shear only, and are free to rotate under gravity load. Type 3, commonly designated as‖semi-rigid‖ framing (partially restrained), assumes that the connections of beams and girders possess a dependent and known moment capacity 1 and the complete flexibility for Type 2. To provide lateral stiffness to the building, especially to those with frames of Type 2 construction, a system of bracing may be designed to resist lateral forces due to wind for earthquake . Wind loads acting on the exterior walls are transmitted by the floor system to braced bents or the shear walls in the steel framing system. If the floor is not sufficiently rigid to transform the loads, a horizontal bracing system muat be provided between bents. Brace bents may be placed in the outside walls, in permanent interior walls, around elevator and stairway shafts, and other service aeras where the bracing will not be an obstruction. If possible, the braced bents should be placed symmetrically across the building to avoid the twisting of the structure about its vertical axis. The distribution of the wind loads to the brace bents should take into account the eccentricity between the line of action of the resultant wind force and the center of resistance of the wind bracing system. The two approaches used to obtain stiffness in regular-shaped buildings are shown in Fig.25-1.In the core-wall type, the lateral load resisting system is integrated with a central utility core. In the bearing-wall type, the exterior walls are braced and stiffened such that the building acts like a huge cantilevered box. The use of the bearing-wall type of bents was a major factor in reducing the cost of the structural framing for both the World Trade Center in New York and the John Hancock Building in Chicago. Bents may be braced in a number of ways. The full diagonal bracing is the most economical type of wind bracing. Its use is somewhat restricted by frequent requirements for window and door openings. Portal bracing is usually more costly and its use is limited to special cases. The Vierendeel type of braced bents has the advantage of being easily treated architecturally and can be used on the outside walls as part of the building façade. Floor system. The floor system of the multi-story building is a more elaborate construction than the type used in industrial buildings. It includes a framing of girder and beams which supports the floor deck. Several types of floor decks are availability 4 to the application of finished floors and ceilings and to the installation of utilities. The selection of a suitable type of floor deck depends on the occupancy requirements, structural adequacy, and cost considerations. The more common types of floor construction in use are: (1) reinforced concrete slabs,(2) concrete-pan system,(3) open-web joist system,(4) cellular steel type, and (5) other adaptations of these four basic-systems. A reinforced concrete slab is appropriate where a high degree of rigidity is desired. This system is one of the heaviest types used for floor construction in steel framed buildings, although the use of lightweight concrete has reduced the dead weight considerably. In the concrete-pan system, the metal pan and the supporting wood planks make up the forms on which the concrete is poured. This result in a ribbed concrete floor which is s lighter floor system than the conventional reinforced concrete slab. One of the lightest types of floor construction is the open-web joist system. The systems consist of a 2 to 20.5. Concrete slab poured in place over ribbed-wire fabric backed by heavy paper laid directly on the joists. The satisfactory design and construction of the joist is assured by adhering to the specifications of the steel Joist Institute. Several types of prefabricated joists are available. Cellular steel floors have weights comparable to the open-web joist system. The concrete on top of the decking usually serves merely as a finishing material, and s low-strength, lightweight concrete is adequate for the purpose. The load-carrying system consists of light gage, cold-formed cellular units. This system facilitates the installation of wiring for utilities because each cell serves as a conduit. Talling building and Steel construction Although there have been many advancements in building construction technology in general. Spectacular archievements have been made in the design and construction of ultrahigh-rise buildings. The early development of high-rise buildings began with structural steel framing.Reinforced concrete and stressed-skin tube systems have since been economically and competitively used in a number of structures for both residential and commercial purposes.The high-rise buildings ranging from 50 to 110 stories that are being built all over the United States are the result of innovations and development of new structual systems. Greater height entails increased column and beam sizes to make buildings more 5 rigid so that under wind load they will not sway beyond an acceptable limit.Excessive lateral sway may cause serious recurring damage to partitions, ceilings.and other architectural details. In addition,excessive sway may cause discomfort to the occupants of the building because their perception of such motion.Structural systems of reinforced concrete,as well as steel,take full advantage of inherent potential stiffness of the total building and therefore require additional stiffening to limit the sway. In a steel structure,for example,the economy can be defined in terms of the total average quantity of steel per square foot of floor area of the building.Curve A in Fig .1 represents the average unit weight of a conventional frame with increasing numbers of stories. Curve B represents the average steel weight if the frame is protected from all lateral loads. The gap between the upper boundary and the lower boundary represents the premium for height for the traditional column-and-beam frame.Structural engineers have developed structural systems with a view to eliminating this premium. Systems in steel. Tall buildings in steel developed as a result of several types of structural innovations. The innovations have been applied to the construction of both office and apartment buildings. Frame with rigid belt trusses. In order to tie the exterior columns of a frame structure to the interior vertical trusses,a system of rigid belt trusses at mid-height and at the top of the building may be used. A good example of this system is the First Wisconsin Bank Building (1974) in Milwaukee. Framed tube. The maximum efficiency of the total structure of a tall building, for both strength and stiffness,to resist wind load can be achieved only if all column element can be connected to each other in such a way that the entire building acts as a hollow tube or rigid box in projecting out of the ground. This particular structural system was probably used for the first time in the 43-story reinforced concrete DeWitt Chestnut Apartment Building in Chicago. The most significant use of this system is in the twin structural steel towers of the 110-story World Trade Center building in New York Column-diagonal truss tube. The exterior columns of a building can be spaced reasonably far apart and yet be made to work together as a tube by connecting them with diagonal members interesting at the centre line of the columns and beams. This simple yet extremely efficient system was used for the first time on the John Hancock 6 Centre in Chicago, using as much steel as is normally needed for a traditional 40-story building. Bundled tube. With the continuing need for larger and taller buildings, the framed tube or the column-diagonal truss tube may be used in a bundled form to create larger tube envelopes while maintaining high efficiency. The 110-story Sears Roebuck Headquarters Building in Chicago has nine tube, bundled at the base of the building in three rows. Some of these individual tubes terminate at different heights of the building, demonstrating the unlimited architectural possibilities of this latest structural concept. The Sears tower, at a height of 1450 ft(442m), is the world’s tallest building. Stressed-skin tube system. The tube structural system was developed for improving the resistance to lateral forces (wind and earthquake) and the control of drift (lateral building movement ) in high-rise building. The stressed-skin tube takes the tube system a step further. The development of the stressed-skin tube utilizes the façade of the building as a structural element which acts with the framed tube, thus providing an efficient way of resisting lateral loads in high-rise buildings, and resulting in cost-effective column-free interior space with a high ratio of net to gross floor area. Because of the contribution of the stressed-skin façade, the framed members of the tube require less mass, and are thus lighter and less expensive. All the typical columns and spandrel beams are standard rolled shapes, minimizing the use and cost of special built-up members. The depth requirement for the perimeter spandrel beams is also reduced, and the need for upset beams above floors, which would encroach on valuable space, is minimized. The structural system has been used on the 54-story One Mellon Bank Center in Pittburgh. Systems in concrete. While tall buildings constructed of steel had an early start, development of tall buildings of reinforced concrete progressed at a fast enough rate to provide a competitive chanllenge to structural steel systems for both office and apartment buildings. Framed tube. As discussed above, the first framed tube concept for tall buildings was used for the 43-story DeWitt Chestnut Apartment Building. In this building, exterior columns were spaced at 5.5ft (1.68m) centers, and interior columns were used as needed to support the 8-in . -thick (20-m) flat-plate concrete slabs. Tube in tube. Another system in reinforced concrete for office buildings 7 combines the traditional shear wall construction with an exterior framed tube. The system consists of an outer framed tube of very closely spaced columns and an interior rigid shear wall tube enclosing the central service area. The system (Fig .2), known as the tube-in-tube system , made it possible to design the world’s present tallest (714ft or 218m)lightweight concrete building ( the 52-story One Shell Plaza Building in Houston) for the unit price of a traditional shear wall structure of only 35 stories. Systems combining both concrete and steel have also been developed, an examle of which is the composite system developed by skidmore, Owings &Merril in which an exterior closely spaced framed tube in concrete envelops an interior steel framing, thereby combining the advantages of both reinforced concrete and structural steel systems. The 52-story One Shell Square Building in New Orleans is based on this system. Steel construction refers to a broad range of building construction in which steel plays the leading role. Most steel construction consists of large-scale buildings or engineering works, with the steel generally in the form of beams, girders, bars, plates, and other members shaped through the hot-rolled process. Despite the increased use of other materials, steel construction remained a major outlet for the steel industries of the U.S, U.K, U.S.S.R, Japan, West German, France, and other steel producers in the 1970s. Early history. The history of steel construction begins paradoxically several decades before the introduction of the Bessemer and the Siemens-Martin (openj-hearth) processes made it possible to produce steel in quantities sufficient for structure use. Many of problems of steel construction were studied earlier in connection with iron construction, which began with the Coalbrookdale Bridge, built in cast iron over the Severn River in England in 1777. This and subsequent iron bridge work, in addition to the construction of steam boilers and iron ship hulls , spurred the development of techniques for fabricating, designing, and jioning. The advantages of iron over masonry lay in the much smaller amounts of material required. The truss form, based on the resistance of the triangle to deformation, long used in timber, was translated effectively into iron, with cast iron being used for compression members-i.e, those bearing the weight of direct loading-and wrought iron being used for tension members-i.e, those bearing the pull of suspended loading. The technique for passing iron, heated to the plastic state, between rolls to form 8 flat and rounded bars, was developed as early as 1800;by 1819 angle irons were rolled; and in 1849 the first I beams, 17.7 feet (5.4m) long , were fabricated as roof girders for a Paris railroad station. Two years later Joseph Paxton of England built the Crystal Palace for the London Exposition of 1851. He is said to have conceived the idea of cage construction-using relatively slender iron beams as a skeleton for the glass walls of a large, open structure. Resistance to wind forces in the Crystal palace was provided by diagonal iron rods. Two feature are particularly important in the history of metal construction; first, the use of latticed girder, which are small trusses, a form first developed in timber bridges and other structures and translated into metal by Paxton ; and second, the joining of wrought-iron tension members and cast-iron compression members by means of rivets inserted while hot. In 1853 the first metal floor beams were rolled for the Cooper Union Building in New York. In the light of the principal market demand for iron beams at the time, it is not surprising that the Cooper Union beams closely resembled railroad rails. The development of the Bessemer and Siemens-Martin processes in the 1850s and 1860s suddenly open the way to the use of steel for structural purpose. Stronger than iron in both tension and compression ,the newly available metal was seized on by imaginative engineers, notably by those involved in building the great number of heavy railroad bridges then in demand in Britain, Europe, and the U.S. A notable example was the Eads Bridge, also known as the St. Louis Bridge, in St. Louis (1867-1874), in which tubular steel ribs were used to form arches with a span of more than 500ft (152.5m). In Britain, the Firth of Forth cantilever bridge (1883-90) employed tubular struts, some 12 ft (3.66m) in diameter and 350 ft (107m) long. Such bridges and other structures were important in leading to the development and enforcement of standards and codification of permissible design stresses. The lack of adequate theoretical knowledge, and even of an adequate basis for theoretical studies, limited the value of stress analysis during the early years of the 20th century,as iccasionally failures,such as that of a cantilever bridge in Quebec in 1907,revealed.But failures were rare in the metal-skeleton office buildings;the simplicity of their design proved highly practical even in the absence of sophisticated analysis techniques. Throughout the first third of the century, ordinary carbon steel, without any special alloy strengthening or hardening, was universally used. The possibilities inherent in metal construction for high-rise building was 9 demonstrated to the world by the Paris Exposition of 1889.for which Alexandre-Gustave Eiffel, a leading French bridge engineer, erected an openwork metal tower 300m (984 ft) high. Not only was the height-more than double that of the Great Pyramid-remarkable, but the speed of erection and low cost were even more so, a small crew completed the work in a few months. The first skyscrapers. Meantime, in the United States another important development was taking place. In 1884-85 Maj. William Le Baron Jenney, a Chicago engineer had designed the Home Insurance Building, ten stories high, with a metal skeleton. Jenney’s beams were of Bessemer steel, though his columns were cast iron. Cast iron lintels supporting masonry over window openings were, in turn, supported on the cast iron columns. Soild masonry court and party walls provided lateral support against wind loading. Within a decade the same type of construction had been used in more than 30 office buildings in Chicago and New York. Steel played a larger and larger role in these , with riveted connections for beams and columns, sometimes strengthened for wind bracing by overlaying gusset plates at the junction of vertical and horizontal members. Light masonry curtain walls, supported at each floor level, replaced the old heavy masonry curtain walls, supported at each floor level , replaced the old heavy masonry. Though the new construction form was to remain centred almost entirely in America for several decade, its impact on the steel industry was worldwide. By the last years of the 19th century, the basic structural shapes-I beams up to 20 in. ( 0.508m) in depth and Z and T shapes of lesser proportions were readily available, to combine with plates of several widths and thicknesses to make efficient members of any required size and strength. In 1885 the heaviest structural shape produced through hot-rolling weighed less than 100 pounds (45 kilograms) per foot; decade by decade this figure rose until in the 1960s it exceeded 700 pounds (320 kilograms) per foot. Coincident with the introduction of structural steel came the introduction of the Otis electric elevator in 1889. The demonstration of a safe passenger elevator, together with that of a safe and economical steel construction method, sent building heights soaring. In New York the 286-ft (87.2-m) Flatiron Building of 1902 was surpassed in 1904 by the 375-ft (115-m) Times Building ( renamed the Allied Chemical Building) , the 468-ft (143-m) City Investing Company Building in Wall Street, the 612-ft (187-m) Singer Building (1908), the 700-ft (214-m) Metropolitan Tower (1909) and, in 1913, the 780-ft (232-m) Woolworth Building. 10 The rapid increase in height and the height-to-width ratio brought problems. To limit street congestion, building setback design was prescribed. On the technical side, the problem of lateral support was studied. A diagonal bracing system, such as that used in the Eiffel Tower, was not architecturally desirable in offices relying on sunlight for illumination. The answer was found in greater reliance on the bending resistance of certain individual beams and columns strategically designed into the skeletn frame, together with a high degree of rigidity sought at the junction of the beams and columns. With today’s modern interior lighting systems, however, diagonal bracing against wind loads has returned; one notable example is the John Hancock Center in Chicago, where the external X-braces form a dramatic part of the structure’s façade. World War I brought an interruption to the boom in what had come to be called skyscrapers (the origin of the word is uncertain), but in the 1920s New York saw a resumption of the height race, culminating in the Empire State Building in the 1931. The Empire State’s 102 stories (1,250ft. [381m]) were to keep it established as the hightest building in the world for the next 40 years. Its speed of the erection demonstrated how thoroughly the new construction technique had been mastered. A depot across the bay at Bayonne, N.J., supplied the girders by lighter and truck on a schedule operated with millitary precision; nine derricks powerde by electric hoists lifted the girders to position; an industrial-railway setup moved steel and other material on each floor. Initial connections were made by bolting, closely followed by riveting, followed by masonry and finishing. The entire job was completed in one year and 45 days. The worldwide depression of the 1930s and World War II provided another interruption to steel construction development, but at the same time the introduction of welding to replace riveting provided an important advance. Joining of steel parts by metal are welding had been successfully achieved by the end of the 19th century and was used in emergency ship repairs during World War I, but its application to construction was limited until after World War II. Another advance in the same area had been the introduction of high-strength bolts to replace rivets in field connections. Since the close of World War II, research in Europe, the U.S., and Japan has greatly extended knowledge of the behavior of different types of structural steel under varying stresses, including those exceeding the yield point, making possible more 11 refined and systematic analysis. This in turn has led to the adoption of more liberal design codes in most countries, more imaginative design made possible by so-called plastic design ?The introduction of the computer by short-cutting tedious paperwork, made further advances and savings possible. Strength under Combined Stress In many structural situations concrete is subjected simultaneously to various stresses acting in various directions. For instance,in beams much of the concrete is subject simultaneously to compression and shear stresses and in slabs and footings to compression in two perpendicular directions plus shear.By methods well knowcan be reduced to three principal stresses acting n in the study of strength of materials, any state of combined stress, no matter how complex, at right angles to each other on an appropriately oriented elementary cube in the material. Any or all of the principal stresses can be either tension or compression. If one of them is zero, a state of biaxial stress is said to exist; if two of them are zero, the state of stress is uniaxial, either simple compression or simple tension. In most cases only the uniaxial strength properties of a material are known from simple tests, such as the cylinder strength f'c and the tensile strength f't. For predicting the strengths of structures in which concrete is subject to biaxial or triaxial stress, it would be desirable to be able to calculate the strength of concrete in such states of stress, knowing from tests only either f'c or f'c and f't. In spite of extensive and continuing research, no general theory of the strength of concrete under combined stress has yet emerged. Modifications of various strength theories , such as the maximum-tension stress, the Mohr-Coulomb, and the octahedral-stress theories, all of which are discussed in strength-of-materials texts, have been adapted with varying partial success to concrete. Current experimental evidence indicates that limiting tensile strain, which is a function of mean normal stress, may be a failure criterion which is generally applicable. At present none of these theories has been generally accepted, and many have obvious internal contradictions. The main difficulty in developing an adequate general strength theory lies in the highly nonhomogeneous nature of concrete and in the degree to which its behavior at high stresses and at fracture is influenced by microcracking and other discontinuity phenomena. However, the strength of concrete has been well established by tests at least 12 for the biaxial state. Results may be presented in the form of an interaction diagram such as Fig.1 which shows the strength in direction 1 as a function of the stress applied in direction 2. All stresses are nondimensionalized in terms of the uniaxial compressive strength f'c. It is seen that in the quadrant representing biaxial compression a strength increase as great as about 20 percent over the uniaxial compressive strength is attained, the amount of increase depending upon the ratio of f2 to f1.In the biaxial tension-stress state, the strength in direction 1 is independent of tension in direction 2. When tension in direction 2 is combined with compression in direction 1, the compressive strength is reduced almost linearly. For example, lateral tension of about half the uniaxial tensile strength will reduce the compressive strength by half compared with the uniaxial compressive strength. This fact is of the greatest importance in predicting cracking in deep beams or shear walls, for example. The Mohr-Coulomb theory can be used to describe in an approximate way the influence of triaxiality on strength.It represents a special form of the Mohr theory and defines a failure envelope such that any Mohr stress circle which is tangent to the envelope represents a combination of stresses that will cause failure of the material. For Mohr's stress circle as used here, the two endpoints of the horizontal diameter are defined by the largest and smallest of the three principal stresses, so that the size and location of the crcle is not influenced by the intermediate principal stress. In Fig. 2 Circle 1 represents failure in simple tension at a stress f't and Circle 2 failure in compression at a stress f'c. The failure envelope can be approximated by two straight lines as shown. From experimental studies the slope of the line tangent to Circle 2 on the compression side has an inclination of 37。. On the tension side, the line is laid from the intercept, tangent to Circle 1. Structural Systems to resist lateral loads Commonly Used structural Systems With loads measured in tens of thousands kips, there is little room in the design of high-rise buildings for excessively complex thoughts. Indeed, the better high-rise buildings carry the universal traits of simplicity of thought and clarity of expression. It does not follow that there is no room for grand thoughts. Indeed, it is with such grand thoughts that the new family of high-rise buildings has evolved. Perhaps more important, the new concepts of but a few years ago have become commonplace in today’ s technology. Omitting some concepts that are related strictly to the materials of construction, 13 the most commonly used structural systems used in high-rise buildings can be categorized as follows: 1.Moment-resisting frames. 2.Braced frames, including eccentrically braced frames. 3.Shear walls, including steel plate shear walls. 4.Tube-in-tube structures. 5.Tube-in-tube structures. 6.Core-interactive structures. 7.Cellular or bundled-tube systems. Particularly with the recent trend toward more complex forms, but in response also to the need for increased stiffness to resist the forces from wind and earthquake, most high-rise buildings have structural systems built up of combinations of frames, braced bents, shear walls, and related systems. Further, for the taller buildings, the majorities are composed of interactive elements in three-dimensional arrays. The method of combining these elements is the very essence of the design process for high-rise buildings. These combinations need evolve in response to environmental, functional, and cost considerations so as to provide efficient structures that provoke the architectural development to new heights. This is not to say that imaginative structural design can create great architecture. To the contrary, many examples of fine architecture have been created with only moderate support from the structural engineer, while only fine structure, not great architecture, can be developed without the genius and the leadership of a talented architect. In any event, the best of both is needed to formulate a truly extraordinary design of a high-rise building. While comprehensive discussions of these seven systems are generally available in the literature, further discussion is warranted here .The essence of the design process is distributed throughout the discussion. Moment-Resisting Frames Perhaps the most commonly used system in low-to medium-rise buildings, the moment-resisting frame, is characterized by linear horizontal and vertical members connected essentially rigidly at their joints. Such frames are used as a stand-alone system or in combination with other systems so as to provide the needed resistance to horizontal loads. In the taller of high-rise buildings, the system is likely to be found inappropriate for a stand-alone system, this because of the difficulty in mobilizing sufficient stiffness under lateral forces. 14 Analysis can be accomplished by STRESS, STRUDL, or a host of other appropriate computer programs; analysis by the so-called portal method of the cantilever method has no place in today’s technology. Because of the intrinsic flexibility of the column/girder intersection, and because preliminary designs should aim to highlight weaknesses of systems, it is not unusual to use center-to-center dimensions for the frame in the preliminary analysis. Of course, in the latter phases of design, a realistic appraisal in-joint deformation is essential. Braced Frames The braced frame, intrinsically stiffer than the moment –resisting frame, finds also greater application to higher-rise buildings. The system is characterized by linear horizontal, vertical, and diagonal members, connected simply or rigidly at their joints. It is used commonly in conjunction with other systems for taller buildings and as a stand-alone system in low-to medium-rise buildings. While the use of structural steel in braced frames is common, concrete frames are more likely to be of the larger-scale variety. Of special interest in areas of high seismicity is the use of the eccentric braced frame. Again, analysis can be by STRESS, STRUDL, or any one of a series of two –or three dimensional analysis computer programs. And again, center-to-center dimensions are used commonly in the preliminary analysis. Shear walls The shear wall is yet another step forward along a progression of ever-stiffer structural systems. The system is characterized by relatively thin, generally (but not always) concrete elements that provide both structural strength and separation between building functions. In high-rise buildings, shear wall systems tend to have a relatively high aspect ratio, that is, their height tends to be large compared to their width. Lacking tension in the foundation system, any structural element is limited in its ability to resist overturning moment by the width of the system and by the gravity load supported by the element. Limited to a narrow overturning, One obvious use of the system, which does have the needed width, is in the exterior walls of building, where the requirement for windows is kept small. Structural steel shear walls, generally stiffened against buckling by a concrete overlay, have found application where shear loads are high. The system, intrinsically 15 more economical than steel bracing, is particularly effective in carrying shear loads down through the taller floors in the areas immediately above grade. The sys tem has the further advantage of having high ductility a feature of particular importance in areas of high seismicity. The analysis of shear wall systems is made complex because of the inevitable presence of large openings through these walls. Preliminary analysis can be by truss-analogy, by the finite element method, or by making use of a proprietary computer program designed to consider the interaction, or coupling, of shear walls. Framed or Braced Tubes The concept of the framed or braced or braced tube erupted into the technology with the IBM Building in Pittsburgh, but was followed immediately with the twin 110-story towers of the World Trade Center, New York and a number of other buildings .The system is characterized by three –dimensional frames, braced frames, or shear walls, forming a closed surface more or less cylindrical in nature, but of nearly any plan configuration. Because those columns that resist lateral forces are placed as far as possible from the cancroids of the system, the overall moment of inertia is increased and stiffness is very high. The analysis of tubular structures is done using three-dimensional concepts, or by two- dimensional analogy, where possible, whichever method is used, it must be capable of accounting for the effects of shear lag. The presence of shear lag, detected first in aircraft structures, is a serious limitation in the stiffness of framed tubes. The concept has limited recent applications of framed tubes to the shear of 60 stories. Designers have developed various techniques for reducing the effects of shear lag, most noticeably the use of belt trusses. This system finds application in buildings perhaps 40stories and higher. However, except for possible aesthetic considerations, belt trusses interfere with nearly every building function associated with the outside wall; the trusses are placed often at mechanical floors, mush to the disapproval of the designers of the mechanical systems. Nevertheless, as a cost-effective structural system, the belt truss works well and will likely find continued approval from designers. Numerous studies have sought to optimize the location of these trusses, with the optimum location very dependent on the number of trusses provided. Experience would indicate, however, that the location of these trusses is provided by the optimization of mechanical systems and by 16 aesthetic considerations, as the economics of the structural system is not highly sensitive to belt truss location. Tube-in-Tube Structures The tubular framing system mobilizes every column in the exterior wall in resisting over-turning and shearing forces. The term‘tube-in-tube’is largely self-explanatory in that a second ring of columns, the ring surrounding the central service core of the building, is used as an inner framed or braced tube. The purpose of the second tube is to increase resistance to over turning and to increase lateral stiffness. The tubes need not be of the same character; that is, one tube could be framed, while the other could be braced. In considering this system, is important to understand clearly the difference between the shear and the flexural components of deflection, the terms being taken from beam analogy. In a framed tube, the shear component of deflection is associated with the bending deformation of columns and girders (i.e, the webs of the framed tube) while the flexural component is associated with the axial shortening and lengthening of columns (i.e, the flanges of the framed tube). In a braced tube, the shear component of deflection is associated with the axial deformation of diagonals while the flexural component of deflection is associated with the axial shortening and lengthening of columns. Following beam analogy, if plane surfaces remain plane (i.e, the floor slabs),then axial stresses in the columns of the outer tube, being farther form the neutral axis, will be substantially larger than the axial stresses in the inner tube. However, in the tube-in-tube design, when optimized, the axial stresses in the inner ring of columns may be as high, or even higher, than the axial stresses in the outer ring. This seeming anomaly is associated with differences in the shearing component of stiffness between the two systems. This is easiest to under-stand where the inner tube is conceived as a braced (i.e, shear-stiff) tube while the outer tube is conceived as a framed (i.e, shear-flexible) tube. Core Interactive Structures Core interactive structures are a special case of a tube-in-tube wherein the two tubes are coupled together with some form of three-dimensional space frame. Indeed, the system is used often wherein the shear stiffness of the outer tube is zero. The United States Steel Building, Pittsburgh, illustrates the system very well. Here, the inner tube is a braced frame, the outer tube has no shear stiffness, and the two systems 17 are coupled if they were considered as systems passing in a straight line from the ―hat‖ structure. Note that the exterior columns would be improperly modeled if they were considered as systems passing in a straight line from the ―hat‖ to the foundations; these columns are perhaps 15% stiffer as they follow the elastic curve of the braced core. Note also that the axial forces associated with the lateral forces in the inner columns change from tension to compression over the height of the tube, with the inflection point at about 5/8 of the height of the tube. The outer columns, of course, carry the same axial force under lateral load for the full height of the columns because the columns because the shear stiffness of the system is close to zero. The space structures of outrigger girders or trusses, that connect the inner tube to the outer tube, are located often at several levels in the building. The AT&T headquarters is an example of an astonishing array of interactive elements: 1.The structural system is 94 ft (28.6m) wide, 196ft(59.7m) long, and 601ft (183.3m) high. 2.Two inner tubes are provided, each 31ft(9.4m) by 40 ft (12.2m), centered 90 ft (27.4m) apart in the long direction of the building. 3.The inner tubes are braced in the short direction, but with zero shear stiffness in the long direction. 4.A single outer tube is supplied, which encircles the building perimeter. 5.The outer tube is a moment-resisting frame, but with zero shear stiffness for the center50ft (15.2m) of each of the long sides. 6.A space-truss hat structure is provided at the top of the building. 7.A similar space truss is located near the bottom of the building 8.The entire assembly is laterally supported at the base on twin steel-plate tubes, because the shear stiffness of the outer tube goes to zero at the base of the building. Cellular structures A classic example of a cellular structure is the Sears Tower, Chicago, a bundled tube structure of nine separate tubes. While the Sears Tower contains nine nearly identical tubes, the basic structural system has special application for buildings of irregular shape, as the several tubes need not be similar in plan shape, It is not uncommon that some of the individual tubes one of the strengths and one of the weaknesses of the system. This special weakness of this system, particularly in framed tubes, has to do with the concept of differential column shortening. The shortening of a column under load 18 is given by the expression?=ΣfL/E For buildings of 12 ft (3.66m) floor-to-floor distances and an average compressive stress of 15 ksi (138MPa), the shortening of a column under load is 15 (12)(12)/29,000 or 0.074in (1.9mm) per story. At 50 stories, the column will have shortened to 3.7 in. (94mm) less than its unstressed length. Where one cell of a bundled tube system is, say, 50stories high and an adjacent cell is, say, 100stories high, those columns near the boundary between .the two systems need to have this differential deflection reconciled. Major structural work has been found to be needed at such locations. In at least one building, the Rialto Project, Melbourne, the structural engineer found it necessary to vertically pre-stress the lower height columns so as to reconcile the differential deflections of columns in close proximity with the post-tensioning of the shorter column simulating the weight to be added on to adjacent, higher columns. Civil engineering Civil engineering is a creative profession. Until the nineteenth century, engineers generally were craftsmen or project organizers who learned their skills through apprenticeship, on-the-job training, or trial and error. With the increase in scientific knowledge, engineering has grown into a profession. Engineering is the practical application of the findings of theoretical science so that they can be put to work for the benefit of mankind. Engineering is one of the oldest occupations in the history of mankind. Without the skills that are included in the field of engineering, our present-day civilization could never have evolved. Concrete Concrete is a rock-like material produced by adding water to a mixture of powdered cement, sand , and stones. Water causes chemical reactions to take place in the cement, and as a result, the paste of cement and water sets hard and grips firmly the sand and stones embedded in it, forming a strong, dense mass. Concrete is a material which is high in compressive strength but low in tensile strength. The tensile strength of concrete is extremely low, about one-tenth of its compressive strength. Cement is a material with adhesive and cohesive properties which enable it to bond mineral fragments. The cements used in building have the property of setting and hardening under water and are usually described as hydraulic cements, with sub-classifications natural, Portland and aluminous. Concrete has been used as a building material for centuries. In the early 19 nineteenth century artificial Portland cement was invented, and this is now the material most commonly used in making concrete for buildings. Concrete and steel are the most commonly used structural materials. They sometimes complement one another, and sometimes compete with one another so that structures of a similar type and function can be built with either of these materials. And yet, the engineer often knows less about the concrete of which the structure is made than about the steel. On a concrete building site the situation is totally different. It is true that the quality of cement is guaranteed by the manufacturer in a manner similar to steel and provided suitable cement is chosen it is hardly ever a cause of faults in a concrete structure. Surprisingly, the ingredients of a good concrete are exactly the same, and it is only the ―know-how‖, often without additional cost of labor, that is responsible for the difference. Interest in the various properties of concrete-density, durability, tensile strength, impermeability, resistance to abrasion, resistance to sulphate attack, and many others-has recently been heightened since modern specifications tend to state requirements for particular properties of concrete rather than simply to stipulate the quality and quantity of the constituent materials. Strength of concrete Strength of concrete is commonly considered its most valuable property, although in many practical cases other characteristics such as durability and impermeability may in fact be more important. Aggregate was originally viewed as an inert material dispersed throughout the cement paste largely for economic reasons. It is possible, however, to take an opposite view and to look on aggregate as a building material connected into a cohesive whole by means of the cement paste, in a manner similar to masonry construction. In fact, aggregate is not truly inert and its physical, thermal, and sometimes also chemical properties influence the performance of concrete. Aggregate is cheaper than cement and it is, therefore, economical to put into the mix as much of the former and as litter of the latter as possible. Curing of Concrete In order to obtain good concrete the placing of an appropriate mix must be followed by curing in a suitable environment during the early stages of hardening. Curing is the name given to procedures used for promoting the hydration of cement. It 20 consists of controlling temperature and moisture movement into and out of the concrete. More specifically, the object of curing is to keep concrete saturated, or as nearly saturated as possible until the originally water-filled space in the fresh cement paste has been filled to the desired extent by the products of the hydration of the cement. In the case of site concrete, active curing nearly always long before the maximum possible hydration has take place. The necessity for curing arises from the fact that the hydration of cement can take place only in water-filled capillaries must be prevented. Furthermore, water lost internally by self-desiccation has to be replace by water from the outside, Self-desiccation is thus of importance in mixes with water/ cement ratios below about 0.5, for higher water/cement ratios the rate of hydration of a sealed specimen equals that of a saturated specimen. This statement is of considerable importance as it was formerly thought that, provided a concrete mix contained water in excess of that required for the chemical reactions with cement, a small loss of water during hardening would not adversely affect the process of hardening and gain of strength. Creep and Shrinkage of Concrete Like many other structural materials, concrete is to a certain degree elastic. Under sustained loading, however, strain increases with time, i.e. concrete exhibits creep. In addition, whether subjected to load or not, concrete contracts on drying, undergoing shrinkage. The relation between stress and strain for concrete is a function of time: the gradual increase in strain with time is due to creep. Creep in concrete members is dependent on the magnitude of the stress, the length of time that the stress has been applied, and the age and strength of the concrete when the stress is applied. In reinforced concrete columns, creep results in a gradual transfer of load from the concrete to the reinforcement. Once the steel yields, any increase in load is taken by the concrete, so that the full strength of both the steel and the concrete is developed before failure takes place—a fact recognized by the design formulae. The loss of pre-stress due to creep is well known and, indeed, accounts for the failure of all early attempts at prestressing. It was only the introduction of high tensile steel, whose elongation is several times the contraction of concrete due to creep and shrinkage that made prestrssing a successful proposition. 21 The importance of shrinkage in structures is largely related to cracking. Material shrinkage may be reduced up to 40%, however, by decreasing the amount of water used in the original mix. This is accomplished by using high plasticizing admixtures allowing for further reduction in the amount of water required, and by curing the concrete at lower temperatures, so that less water is absorbed into the surrounding air as the concrete hardens. Reinforced Concrete Reinforced concrete is by reason of its strength, durability, availability and adaptability an economical material eminently suited for many types of permanent structures. Concrete is relatively strong in compression and can be made sufficiently massive to provide lateral stability. Steel, on the other hand, is strong in tension but often lacks adequate lateral stability in compression due to its slender proportions. A reinforced concrete member in which the concrete resists compression, while the steel resists tension is therefore an ideal structural partnership. The widespread use of concrete in engineering construction stems from its cheapness compared with other structural materials currently available. Its lack of tensile strength is overcome by including reinforcement, usually in the form of steel bars, to produce a composite material known as reinforced concrete. Although the steel reinforcement does not prevent cracking of the concrete in regions of tension, it does prevent the cracks from widening, and it provides an effective means for resisting the internal tensile forces. The quantity of reinforcement needed is usually quite small, relative to the volume of concrete, so that the total cost of reinforced concrete construction remains commercially very competitive. Thus a rectangular arrangement of vertical and horizontal steel bar is introduced into regions of a beam where inclined cracks can form as a result of combined shearing action and bending moment. Cracking in concrete may be caused not only by external loading, but also by temperature gradients and differential or restrained shrinkage. Secondary reinforcement is therefore provided to control such cracking, which may be unsightly and even dangerous. Prestressed concrete Concrete is essentially a compression material. Its strength in tension is much 22 lower than in compression, and in many cases in design the tensile resistance is discounted altogether. The prestressing of concrete, there, naturally involves application of a compressive loading , prior to applying the anticipated design loads, so that tensile stresses that otherwise would occur are reduced or eliminated. In the sense of improved serviceability, such partial prestressing represents a substantial improvement, not only over conventional reinforced concrete construction, but also over the original form of full prestressing which, while eliminating service-load cracking often produced a troublesome upward camber. Pretensioning is a particularly economical method of prestressing, not only because the standardization of design permits reusable steel or fiberglass forms, but also because the simultaneous prestressing of many member at once results in great saving of labor. Although the anchorage fittings remain in place to transfer the main prestressing force to the concrete, grouting improves the performance of the member should it be overloaded, and increases its ultimate flexural strength. Structures To assure the adequate and reliable performance of an engineered structure, the structural engineer must be able to accurately predict the overall response of the structural system to probable disturbances (forces, loads, displacements, etc.). The prediction of this structural response and behavior must be based upon the analysis of a model whose behavior approximates, as closely as is practical, that of the actual conceived structure. Each cycle may also introduce some feedback on the applied loading, as in the case of dynamic conditions which are dependent upon the mass distribution and deformations of the structural model. The structural design itself induces two different tasks, the design of the structure, in which the sizes and locations of the main members are settled, and the analysis of this structure by mathematical or graphical methods or both, to work out how the loads pass through the structure with the particular member chosen. But for any unusual structure the tasks of design and analysis will have to be repeated many times until, after many calculations, a design has been found that is strong, stable and lasting. These floors are generally of reinforced or prestressed concrete because they resist fire better than steel or wood, an important consideration for a tall building. 23 Ribbed floors are therefore lighter than solid floors, but it is more difficult to cast them with holes through them unless these holes are carefully planned beforehand. These bars are very thin and be hidden in a door frame or window frame so that for such a building there need be no noticeable obstruction so sight or horizontal movement in any direction outwards from the core. 译文: 基础 下部结构的类型和作用 下部结构(或称基础)通常是设置在地面以下、并将荷载传递给下面土壤或岩石的结构部分。所以土壤在受荷作用时明显受到压缩，并引起所支撑的建筑物沉降。在基础设计中有两个基本要求，一是结构总的沉降要限制到尽量小的程度，二是要尽可能消除结构物各部分的不均匀沉降。就建筑物被破坏的可能性而言，避免不均匀沉降，即避免同一建筑物的沉降差值比限制均匀的总沉降更为重要。 为了限制上述沉降，必须把建筑物的荷载传递到有足够强度的土层，把荷载分布在该土层足够大的面积上，以减少支撑压力，如果建筑物下就近找不到合适的土层，必须采用深基础，例如桩或沉箱，以便把荷载传递到较深的坚实土层上，如果正好在建筑物的下面就有良好的土层，仅需要用基础或其他手段来扩散荷 载。这样的荷载叫做扩展基础。 扩展基础的种类 基础通常分墙基础和 柱基础，墙基础只不过是比墙稍宽的钢筋混凝土条带，它分散墙体的压力，单柱基础通常是正方形，有时是长方形，都是最简单最经济的形式，如果地产权不允许基础突出外墙，外柱使用这种基础就会有麻烦，在这种情况下，可采用不突出墙柱以外的复式基础或条形基础，在间距小的重载内柱下可采用两柱或更多柱的复式基础，如果这种情况下采用单个基础，它们将完全连在一起。 在有较好承载能力的土层上，单个柱基或复式柱基是扩展基础的最常用形 式，如果土质软或柱荷载大，需要的基础面积将太大而不符合经济要求，在这种情况下，除非根据土壤条件需要深基础，否则就采用板式基础，这种基础是铺在 24 整个建筑物下面的钢筋混凝土实心板。因此可以把结构荷载分布到较大的面积上，从这种基础本身的刚度看，也会减少不均匀沉降，它的最简单形式是从两个发现配筋的混凝土，另一 种刚度更大、且通常是最经济的形式，倒置的肋梁楼盖，主梁在柱列中沿一个方向设置，沿另一个发现设置次梁，次梁通常排列紧密，如果柱列为方形，梁在两个方向的间距相当，板双向配筋，柱底部带柱头的倒置平板也用与板式基础。 影响混凝土基础设计的因素 在一般建筑物中，墙或柱上的荷载竖直的穿给基础，并有基础下面向上的土压力所支撑，如果荷载对称与支撑面积，支撑压力可假设为均匀分布，大家知道这是近似的，埋置在粗颗粒的土中的基础压力在基础中心处大，并向周边减弱，因为粗颗粒土中个别颗粒多少可以滑动，使周边的受荷载土向着土压力低的地方移动。依次相反。在黏土中，靠近基础周边处的土压力比基础中心处高，因为在粘性土中，荷载在基础周边引起抗剪切力，从而增加向上的土压力，人门习惯于不考虑这些不均匀性，因为不均匀性的数值不明，土质变化很大，不均匀性对弯矩的影响很大。 在压缩性土中，基础中心加载，以避免由于基础的一边的支撑压力比另一边的大的多而产生倾斜，单个基础应该与柱对中，墙基础应该与墙对中，偏心荷载的基础可用于较密实的土层，可见，当土层良好时，单独基础约束柱子的转动，除非基础位于岩石之上。 精确的确定应力，特别是对单柱基础而言，在均匀向上的压力作用下，基础底部变成碗型，这将使精确的应力分析大为复杂，目前这种基础的设计方法完全基于两种广泛的实验，都是在伊利诺斯大学完成的，这些实验已经被重新估价，特别是在剪切和斜拉方面，从较新的强度理论观点，进行了重新评价。 多层建筑物 结构框架多层建筑物的框架是梁、次梁、或珩甲、以及柱子的体系，用以承受结构的全部重力荷载和抵抗风荷载和地震力。屋面和楼板系统直接支撑在跨越竖直柱子间距的水平主次梁上。 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 楼层的详图通常可以在水平方向和 竖直方向重复和延伸，以覆盖更大的面积和达到摩天大楼的高度，只是强风或很大的地震荷载要求在框架设计上做一些修改。 在设计结构框架时，应尽早注意电梯井和楼梯井等特殊设施。这些构件穿过若干楼层，决定了某些柱子的固定位置。其他的柱子可以按通常的方式布置，要考虑的是建筑艺术要求和屋面、楼板、墙体和间壁的典型构造。 根据连接的类型和性能，美国框架结构学会 规范 编程规范下载gsp规范下载钢格栅规范下载警徽规范下载建设厅规范下载 允许三种钢框架构造类型，第一类通常叫做“刚架”(连续框架)假设梁与柱子的结合具有足够的刚度以保 25 持相连杆件之间的初始夹角实际不变。第二类通常叫做简支框架，(无约束自由端)就重力荷载而言，假设主次梁的端部仅传递剪力，在重力荷载下，端部可以自由转动，第三类通常叫做半刚度框架，(部分约束)假定主梁和次梁之间的连接具有相关的及已知的抗弯能力，在程度上界于第一类的完全刚性和第二类的完全柔性之间。 为了保证建筑物，特别是第二类构造刚架的侧向刚度，可以设计一个支撑系统来抵抗由于风和地震影响引起的侧向力，作用在外墙上的风荷载通过楼板系统传递给该框架体系的支撑排架和剪力墙，如果楼面没有足够的刚度去传递这些荷载，那么还必须在 排架之间增加水平支撑系统。 支撑排架可以设置在外墙内、永久性内墙内，电梯井和楼梯井周围，以及设在不会给使用造成障碍的其他服务面积内，如果可能，支撑排架最好对称的布置在整个建筑物内，以避免结构绕其竖轴发生扭转，支撑排架在承受风荷载时，应考虑到风的合力作用线与抗风支撑系统的抵抗中心之间的偏心。 规则形状的建筑物为获得刚度而采用的良种方法，在核心墙类型间， 抗侧荷载系统与中央设备核心连成一个整体，在承重墙类型中，外墙被支撑加强了，因此建筑物的作用就如一个巨大的悬臂箱体纽约的世界贸易中心和芝加哥的汉库克大厦之所以能降低结构框架的造价，主要是采用了拍架结构。 排架的支撑方法有多种，最经济的抗风支撑形式是完全对角支撑，但经常由于门窗开洞口的影响，使得这种支撑的采用在一定程度上受到了限制，门架式支撑较贵，只有在特殊情况才使用，格构支撑排架，具有易于建筑处理的特点。因此可用于外墙作为建筑物立面的一部分。 楼面系统 多层房屋的楼面系统比工业建筑的楼面系统更为复杂，它包括支撑楼板的主次梁骨架，有若干种楼板可供挑选，他们具有不同的耐久性、抗火性、重量、以及对铺设地面，天花板和安装设备的不同适应能力，选择合适的楼板适应类性取决与居住要求、合理结构、和造价因素。 比较通用的楼面构造类型:(1)钢筋混凝土板(2)混凝土托盘体系(3)空腹托梁体系(4)蜂窝钢板型(5)这四种基本体系的其他演变类型。 钢筋混凝土板适合于要求刚度大的地方，虽然使用轻混凝土已经大大降低了自重，钢筋混凝土板仍然是用语钢骨架建筑物的楼板构造中最重的体系之一。在混凝土托盘体系中，金属托盘和支撑木板形成了在其上浇注混凝土的 模板 个人简介word模板免费下载关于员工迟到处罚通告模板康奈尔office模板下载康奈尔 笔记本 模板 下载软件方案模板免费下载 ，最后成为比传统钢筋混凝土板轻的类型混凝土楼板体系。 空腹托梁体系是最轻的楼板构造形式之一，在托梁上直接铺设其背面有厚纸的肋形钢丝网，再在其上浇注2 ---20.5英寸的的混凝土板就够成了这种体系，按 26 照规范进行工作，可以保证得到良好的设计和构造，有若干种预制托梁可供挑选。 蜂窝楼板的重量和空腹托梁体系不相上下，板顶上的混凝土通常只做饰面材料，因此，只需要低强度的轻混凝土就足够了，承重体系由薄壁冷弯蜂窝状单元构成，由于每个蜂窝都可以用做导管，所以该体系有利于敷设设备管线。 高层结构与钢结构 近年来，尽管一般的建筑结构设计取得了很大的进步，但是取得显著成绩的还要属超高层建筑结构设计。 最初的高层建筑设计是从钢结构的设计开始的。钢筋混凝土和受力外包钢筒系统运用起来是比较经济的系统，被有效地运用于大批的民用建筑和商业建筑中。50层到100层的建筑被定义为超高层建筑。而这种建筑在美国得广泛的应用是由于新的结构系统的发展和创新。 这样的高度需要增大柱和梁的尺寸，这样以来可以使建筑物更加坚固以至于在允许的限度范围内承受风荷载而不产生弯曲和倾斜。过分的倾斜会导致建筑的隔离构件、顶棚以及其他建筑细部产生循环破坏。除此之外，过大的摇动也会使建筑的使用者们因感觉到这样的的晃动而产生不舒服的感觉。无论是钢筋混凝土结构系统还是钢结构系统都充分利用了整个建筑的刚度潜力，因此不能指望利用多余的刚度来限制侧向位移。 在钢结构系统设计中，经济预算是根据每平方英寸地板面积上的钢材的数量确定的。图示1中的曲线A显示了常规框架的平均单位的重量随着楼层数的增加而增加的情况。而曲线B显示则显示的是在框架被保护而不受任何侧向荷载的情况下的钢材的平均重量。上界和下界之间的区域显示的是传统梁柱框架的造价随高度而变化的情况。而结构工程师改进结构系统的目的就是减少这部分造价。 钢结构中的体系:钢结构的高层建筑的发展是几种结构体系创新的结果。这些创新的结构已经被广泛地应用于办公大楼和公寓建筑中。 刚性带式桁架的框架结构:为了联系框架结构的外柱和内部带式桁架，可以在建筑物的中间和顶部设置刚性带式桁架。1974年在米望基建造的威斯康森银行大楼就是一个很好的例子。 框架筒结构 如果所有的构件都用某种方式互相联系在一起，整个建筑就像是从地面发射出的一个空心筒体或是一个刚性盒子一样。这个时候此高层建筑的整个结构抵抗风荷载的所有强度和刚度将达到最大的效率。这种特殊的结构体系首次被芝加哥的43层钢筋混凝土的德威特红棕色的公寓大楼所采用。但是这种结构体系的的所有应用中最引人注目的还要属在纽约建造的100层的双筒结构的世界贸易中心大厦。 27 斜撑桁架筒体: 建筑物的外柱可以彼此独立的间隔布置，也可以借助于通过梁柱中心线的交叉的斜撑构件联系在一起，形成一个共同工作的筒体结构。这种高度的结构体系首次被芝加哥的John Hancock 中心大厦采用。这项工程所耗用的刚才量与传统的四十层高楼的用钢量相当。 筒体 随着对更高层建筑的要求不断地增大。筒体结构和斜撑桁架筒体被设计成捆束状以形成更大的筒体来保持建筑物的高效能。芝加哥的110层的Sears Roebuck 总部大楼有9个筒体，从基础开始分成三个部分。这些独立筒体中的终端处在不同高度的建筑体中，这充分体现出了这种新式结构观念的建筑风格自由化的潜能。这座建筑物1450英尺(442米)高，是世界上最高的大厦。 薄壳筒体系统:这种筒体结构系统的设计是为了增强超高层建筑抵抗侧力的能力(风荷载和地震荷载)以及建筑的抗侧移能力。薄壳筒体是筒体系统的又一大飞跃。薄壳筒体的进步是利用高层建筑的正面(墙体和板)作为与筒体共同作用的结构构件，为高层建筑抵抗侧向荷载提供了一个有效的途径，而且可获得不用设柱，成本较低，使用面积与建筑面积之比又大的室内空间。 由于薄壳立面的贡献，整个框架筒的构件无需过大的质量。这样以来使得结构既轻巧又经济。所有的典型柱和窗下墙托梁都是轧制型材，最大程度上减小了组合构件的使用和耗费。托梁周围的厚度也可适当的减小。而可能占据宝贵空间的墙上镦梁的尺寸也可以最大程度地得到控制。这种结构体系已被建造在匹兹堡洲的One Mellon银行中心所运用。 钢筋混凝土中的各体系:虽然钢结构的高层建筑起步比较早，但是钢筋混凝土的高层建筑的发展非常快，无论在办公大楼还是公寓住宅方面都成为刚结构体系的有力竞争对手。 框架筒:像上面所提到的，框架筒构思首次被43层的迪威斯公寓大楼所采用。在这座大楼中，外柱的柱距为5.5英尺(1.68米)。而内柱则需要支撑8英寸厚的无梁板。 筒中筒结构 另一种针对于办公大楼的钢筋混凝土体系把传统的剪力墙结构与外框架筒相结合。该体系由柱距很小的外框架与围绕中心设备区的刚性剪力墙筒组成。这种筒中筒结构(如插图2)使得当前世界上最高的轻质混凝土大楼(在休斯顿建造的独壳购物中心大厦)的整体造价只与35层的传统剪力墙结构相当。 钢结构与混凝土结构的联合体系也有所发展。Skidmore ,Owings 和Merrill共同设计的混合体系就是一个好例子。在此体系中，外部的混凝土框架筒包围着内部的钢框架，从而结合了钢筋混凝土体系与钢结构体系各自的优点。在新奥尔 28 良建造的52层的独壳广场大厦就是运用了这种体系。 钢结构是指在建筑物结构中钢材起着主导作用的结构，是一个很宽泛的概念。大部分的钢结构都包括建筑设计，工程技术、工艺。通常还包括以主梁、次梁、杆件，板等形式存在的钢的热轧加工工艺。上个世纪七十年代，除了对其他材料的需求在增长，钢结构仍然保持着对于来自美国、英国、日本、西德、法国等国家的钢材厂钢材的大量需求。 发展历史:早在Bessemer和Siemens-Marton(开放式炉)工艺出现以前，钢结构就已经有几十年的历史了。而直到此工艺问世之后才使得钢材可以大批生产出来供结构所用。对钢结构诸多问题的研究开始于铁结构的使用，当时很著名的研究对象是1977年在英国建造的横跨斯沃河的Coalbrook dale 大桥。这座大桥以及后来的铁桥设计再加上蒸汽锅炉、铁船身的设计都刺激了建筑安装设计以及连接工艺的发展。铁结构对材料的需求量较小是优胜于砖石结构的主要方面。长久以来一直用木材制作的三角桁架也换成铁制的了。承受由直接荷载产生的重力作用的受压构件常用铸铁制造，而承受由悬挂荷载产生的推力作用的受拉构件常用熟铁制造。 把铁加热到塑性状态，使之从卷状转化为扁平状与圆状之间的某一状态的工艺，早在1800年就得以发展了。随后，1819年角钢问世，1894年第一个工字钢被建造出来作为巴黎火车站的顶梁。此工字钢长17.7英尺)(5.4米)。 1851年英国的Joseph Paxtond为伦敦博览会建造了水晶宫。据说当时他已有这样的骨架结构构思:用比较细的铁梁作为玻璃幕墙的骨架。此建筑的风荷载抵抗力是由对角拉杆所提供的。在金属结构的发展历史中，有两个标志性事件:首先是从木桥发展而来的格构梁由木制转化为铁制;其次是锻铁制的受拉构件与铸铁制的受压构件受热后通过铆钉连接工艺的发展。 十九世纪五六十年代，Bessemer 与 Siemens-Martin工艺的发展使钢材的生产能满足结构的需求。钢的受拉强度与受压强度都好于铁。这种新型的金属常被有想象力的工程师所利用，尤其倍受那些参与过英国、欧洲以及美国的道桥建设的工程师的喜爱。 其中一个很好的例子就是Eads大桥(也被称为路易斯洲大桥)(1867-1874)。在这座大桥中，每隔500英尺(152.5米)设有由钢管加强肋形成的拱。英国的Firth of Forth悬索桥设有管件支撑，直径大约为12英尺(3.66米)，长度为350英尺(107)米。这些大桥以及其他结构在引导钢结构的发展，规范的实施，许用应力的设计方面起到了很重要的作用。1907年Quebec悬索大桥的偶然破坏揭露了二十世纪初期由于缺乏足够的理论知识，甚至是缺乏足够的理论研究的基础知识，而导致在应力分析方面出现了很多的不足。但是，这样的损坏却很少出 29 现在金属骨架的办公大楼中。因为尽管在缺乏缜密的分析的情况下，这些建筑也表现出了很高的实用性。在上个世纪中叶，没有经过任何特殊合金强化、硬化过的普通碳素钢已经被广泛地使用了。 在1889年巴黎召开的世界博览会上，金属结构表现出了在超高层建筑运用上的内在潜力。在这次会上，法国著名的桥梁设计师埃非尔展示了他的杰作-300米高的露天开挖的铁塔。无论是它的高度(比著名的金字塔的两倍还高)，架设的速度-人数不多的工作人员仅用几个月的时间就完成了整个工程任务，还是很低的工程造价都使它脱颖而出。 首批摩天大厦:在刚结构发展的同时，美国的另一个是也蓬勃的发展起来了。1884-1885年，芝加哥的工程师Maj.William Le Baron Jennny设计了家庭保险公司大厦。这座大厦也是金属结构的，有十层高。大厦的梁是钢制的，而柱是铸铁所制。铸铁制的过梁支撑着窗洞口上方的砌体，同时也需要铸铁制的柱支撑着。实心砌体的天井与界墙提供抵抗风载的侧向支撑。不到十年的功夫，芝加哥和纽约已经有超过30座办公大楼是利用这种结构。钢材在这些结构中起了非常大的作用。这种结构利用铆钉把梁与柱连接在一起。有时为了抵抗风荷载还是在竖向构件和横向构件的连接点出贴覆上节点板来加固结构。此外，轻型的玻璃幕墙结构代替了老式的重质砌体结构。 尽管几十年来之中建筑形式主要是在美国发展的，但是它却影响着全世界钢材工业的发展。十九世纪的最后几年，基本结构形状工字型钢的厚度已经达到20英寸(0.508米)，非对称的Z字型钢和T型钢可以与有一定宽度和厚度的板相联结，使得构件具体符合要求的尺寸和强度。1885年最重的型钢通过热轧生产出来，每英寸不到100磅(45千克)。到二十世纪六十年代这个数字已经达到每英寸700磅(320千克)。 紧随着钢结构的发展，1988年第一部电梯问世了。安全载客电梯诞生，以及安全经济的钢结构设计方法的发展促使建筑高度迅猛增加。1902年在纽约建造的高286英寸(87.2米)的Flatiron大厦不断地被后来的建筑所超越。这些建筑分别是高375英尺(115米)的时代大厦(1904)，(后来改名为联合化工制品大厦)。1908年在华尔街建造的高468英尺(143米)的城市投资公司大厦，高612 英尺(187米)的星尔大厦，以及700英尺(214米)的都市塔和780英尺高(232米)的Woll worth大厦。 房屋高度与高宽比的不断增加也带来了许多的问题。为了控制道路的阻塞，要对建筑的缩进设计进行限定。侧向支撑的设置也是其中一项技术问题，例如，埃非尔铁塔所采用的对角支撑体系对于要靠太阳光来照明的办公大厦就不实用了。而只有考虑到具体的单独梁与单独柱的抗弯能力以及梁柱相交处的刚度的框 30 架设计才是可靠的。随着现代内部采光体系的不断发展，抵抗风荷载的对角支撑又重新被利用起来了。芝加哥的John Hancock 中心就是一个很显著的例子。外部的对角支撑成为此结构立面的一个很显眼的部分。 第一次世界大战暂时中断了所谓摩天大厦(当时这个词并没有确定)的蓬勃发展，但是二十世纪二十年代又恢复了这一趋势。1931年建造的帝国大厦把词潮流推向了顶峰。102层高1250英尺(381米)的帝国大厦在后来的40年一直保持着世界最高的地位。它的建造速度充分证明了这种新的结构形式已经被当时的技术所掌握。次项工程所需要的梁是由Bayonne海湾对岸的军械库所提供的。是由用精密仪器控制的驳船和卡车负责运输的。由九架起重机将这些梁提升到指定的位置。由工业轨道装置把钢材和其他材料移到每一层上去。先是螺栓连接紧接着铆钉连接，最后是装修，整个工程的最终完成只用了一年零45天。 二十世纪三十年代席卷全世界的大萧条以及第而次世界大战使钢结构的发展又一次受到了阻碍。但是与此同时，焊接代替了铆钉连接则是一个很重要的发展。 十九世纪末，利用焊接把各个钢零件相连接已取得了很好的成绩，并在第一次世界大战中被运用于救生船的修理。但直到第二次世界大战后才用于建筑结构中。同时在连接领域中又一进步就是高强螺栓代替了铆钉。 二战结束后，欧洲，美国，日本等国都扩大了对在不定应力(包括超过屈服点的情况)作用下各种结构钢的性质的研究，并进行了更为精确、系统的分析。此后，许多国家采用了一些更为自由灵活的 设计规范 民用建筑抗震设计规范配电网设计规范10kv变电所设计规范220kv变电站通用竖流式沉淀池设计 和更为理想化的弹性设计规范。计算机在工程上的运用代替了冗长的手工计算，从而更加促进了钢结构的发展，并大大的减低了造价。 在复合应力作用下的(混凝土)强度 在许多结构中,混凝土同时受到不同方向各种应力的作用.例如在梁中大部分混凝土同时承受压力和剪力,再楼板和基础中,混凝土同时承受两个相互垂直方向的压力外加剪力的作用.根据材料力学学习中已知的方法,无论怎样复杂的复合应力状态,都可化为三个相互垂直的主应力,它们作用在材料适当定向的单元立方体上.三个主应力中的任意一个或者全部既可是拉应力,也可是压应力.如果其中一个主应力为零,则为双轴应力状态。如果有两个主应力为零，则为单轴应力状态，或为简单压缩或为简单拉伸。在多数情况下，根据简单的试验，如圆柱体强度f'c和抗拉强度f't，只能够确定材料在单轴应力作用下的性能。为了预测混凝土在双轴应力或三轴应力作用下的结构强度，在通过试验仅仅知道f'c 或f'c与f't的情况下，需要通过计算确定混凝土在上述复合应力状态下的强度。 尽管人们连续不断地进行了大量的研究，但仍然没有得出有关混凝土在复合 31 应力作用下的强度的通用理论。经过修正的各种强度理论，如最大拉应力理论、莫尔-库仑理论和八面体应力理论 (以上理论都在材料力学课本中讨论过)应用于混凝土，取得了不同程度的进展。现在的试验结果表明，极限拉应变 (它是平均正应力的函数)可能是一个通用的混凝土破坏标准。目前这些理论中没有一个被普遍接受，其中许多还有明显的自相矛盾的地方。建立一个通用的强度理论的主要困难在于混凝土的高度非均质特性和混凝土在高应力下和断裂时，其性能受微小裂缝和其他不连续现象的影响程度较大。 然而，至少对双轴应力的各种试验确定了混凝土的强度。各种试验结果可用图1这样的相互作用图的形式表现出来。该图把朝方向1的强度表示为作用在方向2的应力的函数。所有的应力都根据单轴抗压强度f'c而无量纲化了。在表示双轴压力的象限中可以看出，其强度可达到比单轴抗压强度大20%左右，强度增加的量取决于f2和f1的比值。在双轴受拉情况下，方向1的强度与方向2的拉应力无关。当方向2的拉应力与方向1的压应力同时作用时，抗压强度几乎呈线性下降。例如，大约是单轴抗拉强度的一半的横向拉应力，将使抗压强度减小到单轴抗压强度的一半。这一点在预测深梁或剪力墙内裂缝的出现方面具有非常重要的意义。 混凝土三轴强度的实验研究很少，主要是因为在三个方向同时加荷实际上难以避免由加荷设备产生的很大约束。根据现有资料，关于混凝土三轴强度可得出以下初步结论:(1)在三轴压应力相等状态下，混凝土的强度可能比单轴抗压强度高一个数量级，(2)对于双轴压应力相等并在第三个方向上有一较小的压应力的状态，其强度可指望增加20%以上，(3)在压应力与至少另外一个方向的拉应力同时作用的应力状态下，中间主应力是无足轻重的，抗压强度可以根据图1可靠地预计出来。 莫尔-库仑理论可用来近似地描述三轴应力对强度的影响。它代表莫尔理论的特殊形式，规定材料破坏的包络线，使任何一个与包络线相切的莫尔应力圆都代表引起材料破坏的复合应力。对于此处的莫尔应力圆，水平直径的两个端点由三个主应力中的最大和最小主应力所决定，因此应力圆的大小和位置不受中间主应力的影响。图2中的应力圆1表示应力为f't时简单拉伸引起的破坏，而应力圆2表示应力为f'c时的压力破坏。破坏的包络线可以近似地用两条直线表示，如图。试验研究表明，在受压一侧与应力圆2相切的直线具有37。的倾角。在受拉一侧，直线是一截线，与应力圆1相切 抗侧向荷载的结构体系 常用的结构体系 若已测出荷载量达数千万磅重，那么在高层建筑设计中就没有多少可以进行极其复杂的构思余地了。确实，较好的高层建筑普遍具有构思简单、表现明晰的 32 特点。 这并不是说没有进行宏观构思的余地。实际上，正是因为有了这种宏观的构思，新奇的高层建筑体系才得以发展，可能更重要的是:几年以前才出现的一些新概念在今天的技术中已经变得平常了。 如果忽略一些与建筑材料密切相关的概念不谈，高层建筑里最为常用的结构体系便可分为如下几类: 1.抗弯矩框架。 2.支撑框架，包括偏心支撑框架。 3.剪力墙，包括钢板剪力墙。 4.筒中框架。 5.筒中筒结构。 6.核心交互结构。 7.框格体系或束筒体系。 特别是由于最近趋向于更复杂的建筑形式，同时也需要增加刚度以抵抗几力和地震力，大多数高层建筑都具有由框架、支撑构架、剪力墙和相关体系相结合而构成的体系。而且，就较高的建筑物而言，大多数都是由交互式构件组成三维陈列。 将这些构件结合起来的方法正是高层建筑设计方法的本质。其结合方式需要在考虑环境、功能和费用后再发展，以便提供促使建筑发展达到新高度的有效结构。这并不是说富于想象力的结构设计就能够创造出伟大建筑。正相反，有许多例优美的建筑仅得到结构工程师适当的支持就被创造出来了，然而，如果没有天赋甚厚的建筑师的创造力的指导，那么，得以发展的就只能是好的结构，并非是伟大的建筑。无论如何，要想创造出高层建筑真正非凡的设计，两者都需要最好的。 虽然在文献中通常可以见到有关这七种体系的全面性讨论，但是在这里还值得进一步讨论。设计方法的本质贯穿于整个讨论。设计方法的本质贯穿于整个讨论中。 抗弯矩框架 抗弯矩框架也许是低，中高度的建筑中常用的体系，它具有线性水平构件和垂直构件在接头处基本刚接之特点。这种框架用作独立的体系，或者和其他体系结合起来使用，以便提供所需要水平荷载抵抗力。对于较高的高层建筑，可能会发现该本系不宜作为独立体系，这是因为在侧向力的作用下难以调动足够的刚度。 我们可以利用STRESS，STRUDL 或者其他大量合适的计算机程序进行结 33 构分析。所谓的门架法分析或悬臂法分析在当今的技术中无一席之地，由于柱梁节点固有柔性，并且由于初步设计应该力求突出体系的弱点，所以在初析中使用框架的中心距尺寸设计是司空惯的。当然，在设计的后期阶段，实际地评价结点的变形很有必要。 支撑框架 支撑框架实际上刚度比抗弯矩框架强，在高层建筑中也得到更广泛的应用。这种体系以其结点处铰接或则接的线性水平构件、垂直构件和斜撑构件而具特色，它通常与其他体系共同用于较高的建筑，并且作为一种独立的体系用在低、中高度的建筑中。 尤其引人关注的是，在强震区使用偏心支撑框架。 此外，可以利用STRESS，STRUDL，或一系列二维或三维计算机分析程序中的任何一种进行结构分析。另外，初步分析中常用中心距尺寸。 剪力墙 剪力墙在加强结构体系刚性的发展过程中又前进了一步。该体系的特点是具有相当薄的，通常是(而不总是)混凝土的构件，这种构件既可提供结构强度，又可提供建筑物功能上的分隔。 在高层建筑中，剪力墙体系趋向于具有相对大的高宽经，即与宽度相比，其高度偏大。由于基础体系缺少应力，任何一种结构构件抗倾覆弯矩的能力都受到体系的宽度和构件承受的重力荷载的限制。由于剪力墙宽度狭狭窄受限，所以需要以某种方式加以扩大，以便提从所需的抗倾覆能力。在窗户需要量小的建筑物外墙中明显地使用了这种确有所需要宽度的体系。 钢结构剪力墙通常由混凝土覆盖层来加强以抵抗失稳，这在剪切荷载大的地方已得到应用。这种体系实际上比钢支撑经济，对于使剪切荷载由位于地面正上方区域内比较高的楼层向下移特别有效。这种体系还具有高延性之优点，这种特性在强震区特别重要。 由于这些墙内必然出同一些大孔，使得剪力墙体系分析变得错综复杂。可以通过桁架模似法、有限元法，或者通过利用为考虑剪力墙的交互作用或扭转功能设计的专门计处机程序进行初步分析 框架或支撑式筒体结构: 框架或支撑式筒体最先应用于IBM公司在Pittsburgh的一幢办公楼，随后立即被应用于纽约双子座的110层世界贸易中心摩天大楼和其他的建筑中。这种系统有以下几个显著的特征:三维结构、支撑式结构、或由剪力墙形成的一个性质上差不多是圆柱体的闭合曲面，但又有任意的平面构成。由于这些抵抗侧向荷载的柱子差不多都被设置在整个系统的中心，所以整体的惯性得到提高，刚度也是 34 很大的。 在可能的情况下，通过三维概念的应用、二维的类比，我们可以进行筒体结构的分析。不管应用那种方法，都必须考虑剪力滞后的影响。 这种最先在航天器结构中研究的剪力滞后出现后，对筒体结构的刚度是一个很大的限制。这种观念已经影响了筒体结构在60层以上建筑中的应用。设计者已经开发出了很多的技术，用以减小剪力滞后的影响，这其中最有名的是桁架的应用。框架或支撑式筒体在40层或稍高的建筑中找到了自己的用武之地。除了一些美观的考虑外，桁架几乎很少涉及与外墙联系的每个建筑功能，而悬索一般设置在机械的地板上，这就令机械体系设计师们很不赞成。但是，作为一个性价比较好的结构体系，桁架能充分发挥它的性能，所以它会得到设计师们持续的支持。由于其最佳位置正取决于所提供的桁架的数量，因此很多研究已经试图完善这些构件的位置。实验表明:由于这种结构体系的经济性并不十分受桁架位置的影响，所以这些桁架的位置主要取决于机械系统的完善，审美的要求， 筒中筒结构: 筒体结构系统能使外墙中的柱具有灵活性，用以抵抗颠覆和剪切力。“筒中筒”这个名字顾名思义就是在建筑物的核心承重部分又被包围了第二层的一系列柱子，它们被当作是框架和支撑筒来使用。配置第二层柱的目的是增强抗颠覆能力和增大侧移刚度。这些筒体不是同样的功能，也就是说，有些筒体是结构的，而有些筒体是用来支撑的。 在考虑这种筒体时，清楚的认识和区别变形的剪切和弯曲分量是很重要的，这源于对梁的对比分析。在结构筒中，剪切构件的偏角和柱、纵梁(例如:结构筒中的网等)的弯曲有关，同时，弯曲构件的偏角取决于柱子的轴心压缩和延伸(例如:结构筒的边缘等)。在支撑筒中，剪切构件的偏角和对角线的轴心变形有关，而弯曲构件的偏角则与柱子的轴心压缩和延伸有关。 根据梁的对比分析，如果平面保持原形(例如:厚楼板)，那么外层筒中柱的轴心压力就会与中心筒柱的轴心压力相差甚远，而且稳定的大于中心筒。但是在筒中筒结构的设计中，当发展到极限时，内部轴心压力会很高的，甚至远远大于外部的柱子。这种反常的现象是由于两种体系中的剪切构件的刚度不同。这很容易去理解，内筒可以看成是一个支撑(或者说是剪切刚性的)筒，而外筒可以看成是一个结构(或者说是剪切弹性的)筒。 核心交互式结构: 核心交互式结构属于两个筒与某些形式的三维空间框架相配合的筒中筒特殊情况。事实上，这种体系常用于那种外筒剪切刚度为零的结构。位于Pittsburgh的美国钢铁大楼证实了这种体系是能很好的工作的。在核心交互式结构中，内筒 35 是一个支撑结构，外筒没有任何剪切刚度，而且两种结构体系能通过一个空间结构或“帽”式结构共同起作用。需要指出的是，如果把外部的柱子看成是一种从“帽”到基础的直线体系，这将是不合适的;根据支撑核心的弹性曲线，这些柱子只发挥了刚度的15%。同样需要指出的是，内柱中与侧向力有关的轴向力沿筒高度由拉力变为压力，同时变化点位于筒高度的约5/8处。当然，外柱也传递相同的轴向力，这种轴向力低于作用在整个柱子高度的侧向荷载，因为这个体系的剪切刚度接近于零。 把内外筒相连接的空间结构、悬臂梁或桁架经常遵照一些规范来布置。美国电话电报总局就是一个布置交互式构件的生动例子。 1.结构体系长59.7米，宽28.6米，高183.3米。 2.布置了两个筒，每个筒的尺寸是9.4米×12.2米，在长方向上有27.4米的间隔。 3.在短方向上内筒被支撑起来，但是在长方向上没有剪切刚度。 4.环绕着建筑物布置了一个外筒。 5.外筒是一个瞬时抵抗结构，但是在每个长方向的中心15.2米都没有剪切刚度。 6.在建筑的顶部布置了一个空间桁架构成的“帽式”结构。 7.在建筑的底部布置了一个相似的空间桁架结构。 8.由于外筒的剪切刚度在建筑的底部接近零，整个建筑基本上由两个钢板筒来支持。 框格体系或束筒体系结构: 位于美国芝加哥的西尔斯大厦是箱式结构的经典之作，它由九个相互独立的筒组成的一个集中筒。由于西尔斯大厦包括九个几乎垂直的筒，而且筒在平面上无须相似，基本的结构体系在不规则形状的建筑中得到特别的应用。一些单个的筒高于建筑一点或很多是很常见的。事实上，这种体系的重要特征就在于它既有坚固的一面，也有脆弱的一面。 这种体系的脆弱，特别是在结构筒中，与柱子的压缩变形有很大的关系，柱子的压缩变形有下式计算: ?=ΣfL/E 对于那些层高为3.66米左右和平均压力为138MPa的建筑，在荷载作用下每层柱子的压缩变形为15(12)/29000或1.9毫米。在第50层柱子会压缩94毫米，小于它未受压的长度。这些柱子在50层的时候和100层的时候的变形是不一样的，位于这两种体系之间接近于边缘的那些柱需要使这种不均匀的变形得以调解。 36 主要的结构工作都集中在布置中。在Melbourne的Rialto项目中，结构工程师发现至少有一幢建筑，很有必要垂直预压低高度的柱子，以便使柱不均匀的变形差得以调解，调解的方法近似于后拉伸法，即较短的柱转移重量到较高的邻柱上。 土木工程是一个创造性的职业。19世纪以前，工程师们一般都是手艺人或是工程项目的组织者，他们都是通过学徒，在职训练，或是从不断摸索中学到技术的。随着科学知识的增长，土木工程就发展成为一种职业。 土木工程是建筑科学理论的具体应用，因此，可使它们为人类造福。在人类历史上，土木工程是最古老的一种职业。没有土木工程技术的发展也没有今天城市化的演化。 混凝土 混凝土是一种类似石头的材料，它是把水加入强度水泥、砂和骨料的混合物中而形成的。在水泥中水引起了化学反应，结果，水泥浆和水牢固的结合在一起，并把砂子和骨料牢固的嵌入里面，就形成了坚固、密实的物质。混凝土是一种有很高抗压强度低抗拉强度的材料。混凝土的抗拉强度非常的低，大约为抗压强度的十分之一。 水泥是一种有着黏结力和固结力特性的材料，它能够把各种矿物颗粒很好的结合到一起。用于建筑的水泥具有在水中凝结和硬化的性能，通常称作水硬水泥，又细分为天然水泥、波特兰水泥和矾土水泥 混凝土作为建筑材料已经好几个世纪了。在十九世纪早期，人造波兰特水泥就被发明了，现在这种材料还广泛的用于建造房屋的混凝土中。混凝土和钢筋是最普通的建筑材料。它们有时互相补充，有时相互作用，因此这些材料可用于建造形式相似和功能的建筑物。而且，工程师一般知道的结构混凝土比钢筋要少。 在混凝土结构中是不同的。确实,水泥的质量如同钢材一样,也是由生产厂家来保证的,只要选择适当的水泥,它就决不会成为混凝土结构不合格的原因。 令人惊奇的是,优质混凝土配料的各组分与劣质混凝土的完全相同,而正是这种“专门技术‖(然而往往无需增加工作量)决定着两种混凝土的差别。 近年来对混凝土的各种性能如密实度，耐久性，抗拉强度，抗渗透性，耐磨性，抗硫酸盐浸蚀以及其他一些性能的兴趣大为增长，因为现代规范需要阐明对混凝土特殊性能的要求，而不是简单地规范混凝土组成材料的数量和质量。 混凝土的强度 混凝土的强度通常被认为它具有价值的性能实际上是很重要的，在许多实际的工程中另一些特性，例如耐久性和抗渗透性。 骨料一般被认为是一种惰性材料，由于经济原因认为它和水泥不能很好的黏 37 结。但从相反的观点来看，也可把骨料看成是一种建筑材料，借助于水泥浆，就像圬工建筑一样，连接成一个粘聚性整体。事实上，骨料不是真正的惰性材料，它的物理特性温度，化学特性影响着混凝土的质量。 骨料比水泥便宜，因此，在混凝土拌合料中尽量多用骨料而少用水泥是经济的。 混凝土的养护 在早期硬化阶段，混凝土在适宜的环境中养护，适当的混合得到优质的混凝土。养护是用于提高水泥水化的一种措施，它通过控制温度和湿度使混凝土完全硬化。 更确切的说，养护的目的是要使混凝土保持或尽可能接近于饱和状态，直至新鲜水泥浆中原始充水空间为水泥水化物填充到所要求的程度为止。在混凝土中,在水化达到接近最大值时养护作用开始发生. 养护的必要性事实上是水泥的水化作用只发生在充水的毛细管中。由于这个原因，必须阻止一些水从毛细管中蒸发，而且水蒸发形成的自干作用必然被外界的水所代替。 因此，自干作用在水灰比低于0.5左右的拌和物中才有其重要性;至于在高水灰比的情况下，密封试件的水化速度则与饱和试件的水化速度相同。这一说明十分重要，因为原先曾认为只要混凝土拌和物水量超过与水泥水化反应所需用水量，则在硬化期间即使有少量的失水也不会对硬化过程和强度的增长产生有害的影响。 混凝土的徐变与收缩 如同许多其他的建筑材料混凝土存在着一定程度的弹性，然而，在持续的荷载作用下，随着时间的增长应变也增长。例如:混凝土出现徐变现象，另外，无论构件是否承受荷载，混凝土因干燥缩小产生收缩。 混凝土的应变与应力的关系是一个时间函数，一般随着时间应变的增长是由于混凝土徐变。 混凝土构件的徐变量与应力的大小,应力作用时间的长短,施加应力时混凝土的龄期与强度等都有关系。 在钢筋混凝土柱中，徐变一般会导致荷载从混凝土传到钢筋混凝土构件上。一旦钢筋发生屈服，荷载的任何增加都要混凝土承受，因此。在破坏之前钢筋与混凝土二者的强度都得到充分利用——这一性质已为设计公式所采用。 众所周知，由于混凝土的徐变产生的预应力的损失。确实，它是造成所有构件预应力损失的原因。只有采用了高强度钢筋，其延伸率数倍于混凝土徐变与收缩引起的缩短，预应力技术才获得成功。 38 结构中混凝土的收缩的重要性在于很大程度上会导致裂缝。然而，在普通的混合中通过减少用水量，材料收缩可能会减少到40%。减少用水量是通过采用高性能的塑化剂以进一步降低用水量，并采取在较低的温度下养护混凝土，使混凝土硬化时周围的空气所吸收的水分较少来实现的。 钢筋混凝土 钢筋混凝土因其强度大，经久耐用，可获量大，适应性强而成为一种很适合许多永久型建筑物的经济的建筑材料。 混凝土的抗拉强度相对的教高，能够有足够的物质去提供稳定性。另一方面，钢筋抗拉强，但是由于它的柔弱的特性会缺少足够的抗压稳定性。钢筋混凝土构件中的混凝土抵抗压力，钢筋抵抗拉力，因而是一个理想的结构关系。 与当前可行的其他建筑材料相比，建筑结构工程中混凝土的广泛应用来源于它的经济性。它缺少的抗拉强度是通过钢筋来克服的，通常，在钢筋形式中，生产一种复合材料称为钢筋混凝土。 虽然钢筋不能防止混凝土受拉区裂缝的产生，但确实能限制裂缝的发展，因此提供了抵抗内拉力的有效手段。 比起混凝土的用量，钢筋的数量通常需要的少，因此钢筋混凝土建筑物的总造价在商业上保持着竞争性。 因而在由于剪切和弯曲联合作用而使梁产生斜裂缝的区域要放置成矩形配置的垂直钢筋和水平钢筋。 混凝土的开裂可能是由外界的荷载引起的，也可能由温度梯度引起的。因此，辅助钢筋能够控制这种可能细微甚至危险的裂缝。 预应力混凝土 混凝土是一种基本的抗压的材料。它的抗拉强度比抗压强度要低，在许多的设计中忽略它的抗拉强度。这里所说的预应力混凝土一般包括抗压力的应用，预先的在混凝土中施加设计的载荷，以致于抗拉强度的减少或消失。因此，对混凝土预加应力，本质上就是在施加预期的设计荷载之前施加应力载荷，以使不然会出现的拉应力得以减少或被消除。 从改善使用性能的意义上来说，这样的部分预加应力，不仅比普通钢筋混凝土结构，而且比原来的全预应力方式，都显示出其重大改进，全预应力方式虽然消除了使用载荷下的裂缝，但往往产生令人伤脑筋的上拱度。 先张法是一种非常经济的施加预应力的方法，不仅是由于设计的标准化可以重复利用钢模或玻璃纤维板，而且也是因为同时对许多构件迅速的施加预应力，结果大大节省劳力。 虽然锚固装置在本身位置就将预张拉力传给混凝土。然而压浆可改善构件在 39 超载时的工作性能，并增加构件的极限抗弯强度 结构 为了假定一个结构工程的可靠性和稳定性，当遇到可能的干扰(外力、荷载、移动等)，建筑工程师必须精确的预测这整个结构的反应。结构的这种反应和性能的预测必须基于对其性能与实际构想结构性能尽可能接近的模型所进行的分析。 正像在取决于质量分布和结构模型变形的动态条件情况下一样，每次循环也都可能对施加的荷载产生一些相应的反应。 结构设计本身包括两项不同的任务，即决定主要构件尺寸和布置的结构设计和用数学方法或图解方法或两者并用对该结构进行分析，以计算出在采用了所选特定构件的结构物中荷载是如何传递的。 但对任何一个异乎寻常的结构，分析和设计工作必须重复多次，直到经过多次计算之后，得到一个坚固、稳定而耐久的设计 方案 气瓶 现场处置方案 .pdf气瓶 现场处置方案 .doc见习基地管理方案.doc关于群访事件的化解方案建筑工地扬尘治理专项方案下载 为止。 这些楼板通常为钢筋混凝土或是预应力混凝土，因为它们的耐久性能比钢和木材的好，这对高层建筑来说，是一个重要的考虑因素。 因而肋式楼板比实心楼板要轻得多，但要浇注具有贯穿孔洞的肋式楼板是比较困难的，除非事先把这些孔洞仔细的布置好。 这些钢筋很细，可以隐藏在门框或窗框里，因此，这种建筑物对视线不至于有明显的障碍，或不至于妨碍人们从核心部分往外向任何方向的水平往来活动。 40