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GB50011
Note: This is not complete or authoritative, and is not a substitute for the code. It has not yet been
QA'd.
The Chinese "Code for Seismic Design of Buildings" is published by the China Architecture and
Building Press.
The following information is based on the English translation.The focus is on design in Macau to the
Chinese Seismic Code (which approach has been approved by the Macau Building Department). The
Macau Seismic Codeis less developed than the Chinese Seismic Code, so the building authority
permits use of other codes.
GB50011-2001
The latest Chinese seismic building code is the 2001 edition of the GB50011 - 2001 "Code for
seismic design of buildings". It has been revised by the "China Academy of Building
Research" (CABR), and it replaces GBJ 11-89, published in 1994. An English translation of this
code is available (ISBN 7-112-07528-9 [1] (http://www.china-abp.com.cn/)[2] (http://www.china-
building.com.cn/)).
Contents
� 1 GB50011-2001
� 1.1 General Comments
� 1.2 Performance Objectives
� 1.2.1 Level 1
� 1.2.2 Level 2
� 1.2.3 Level 3
� 1.3 Importance Categories
� 1.4 Site Classification
� 1.5 Characteristic Period
� 1.6 Seismic Influences (seismic zone coefficients)
� 1.7 Design Response Spectrum
� 1.8 Seismic Coefficient Graph - Design Basic Acceleration of Ground Motion
� 1.9 Seismic Detailing Requirements
� 1.10 Structural Regularity
� 1.11 Analysis Methods
� 1.12 Load Combinations
� 1.13 Macau
� 1.14 Table of Contents of Code
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Additional notes are available from Raymond Koo and will be incorporated over time..
General Comments
For seismic design, the Chinese approach is rather like the Japanese approach and similar to
performance-based FEMA 356, with multiple performance objectives.
Seismic zones are defined by intensities. The design intensity ("local fortification intensity") may be
taken from the "seismic basic intensity" on the "China Seismic Ground Motion Parameter Zonation
Map" or from Appendix A. These intensities (level 2) are associated with ground accelerations and
can be considered to be equivalent to the design basis earthquake in the IBC and Eurocode 8. Design
checks are carried out for the frequent earthquake (level 1). If the structure is irregular (in elevation,
plan, or by virtue of being too tall), then non-linear dynamic analysis to level 3 (rare earthquake)
may be required.
Design checks (strength and deformation) should be carried out for the frequent earthquake only
(level 1) unless analysis of deformations to the rare earthquake (level 3) is required or recommended
by the clauses in section 5.5.2. No analysis to the level 2 earthquake is required.
Other codes also govern seismic design, and these provisions may add to the requirements in
GB50011.
Performance Objectives
Three levels of design seismic event are defined:
� Level 1 - Frequent earthquake
� Level 2 - "Local fortification intensity earthquake"
� Level 3 - Rare earthquake
Level 1
Level 1 seismic design is done to size member to respond elastically within member strength
capacity limits, with load factors and material safety factors. The performance objective is that
buildings should either not be damaged or only slightly damaged without affecting use.
This performance level is roughly equivalent to the "immediate occupancy" structural performance
level in FEMA 356 terms. The return period is 50 years. The PHGA can be obtained from Table
5.1.4-1 on page 28. For Macau in zone 7 and a 0.1g PHGA for a 475 year event, the PGHA = 0.08g
x 0.45 = 0.036g. The maximum value on the response spectrum curve alfa max = 0.08g.This alfa
max is the same as the IBC spectral acceleration at 0.2 sec.
The elastic response spectrum is determined on page 29. There is no force reduction factor for level
one, since this is an elastic design for a frequent seismic event. Members should be sized according
to various load combinations (Table 5.1.3) and a 1.3 load factor for the seismic load, as on page 36,
eqn 5.4.1. The Chinese code requires much more stiffness than US codes so as to minimise non-
structural damage. The interstorey drifts must be limited to values in Table 5.5.1 on page 38.
The gamma_RE factor increases the member seismic resistance strength capacity by about 10% (non
ductile actions) - 25% (ductile actions). This is similar to the Japanese code for an increase in
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material short term yielding strength by about 30%. The Chinese code explanation is that this is a
reliability adjustment factor to consider the short term and accidental nature of the seismic action.
The reliability on member strength capacities can be relaxed to some degree compared with those
required to resist permanent actions (gravity) and long term actions (wind).
Level 2
The Level 2 is for the 475 year event. For normal buildings the performance of this level is not
checked explicitly. The code assumes that this level of performance is implicitly satisfied if the level
1 and level 3 performance objective have been satisfied. The performance objective is that while
the building may be damaged, it may be returned to use with or without repair.
Level 3
The level 3 is for the 2,500 year event. Explicit checks must be carried out to limit the interstorey
drifts to acceptable levels as on page 40, Table 5.5.5. And as in other codes, ductile detailing
according to later sections in the code for steel, RC, masonry and hybrid steel-RC etc. The
performance objective is "Collapse Prevention".
Importance Categories
These are defined in section 3.1 (page 5).
� Category A - major buildings, or those where failure would result in secondary disasters
� Category B - buildings where continued function is required (or at least rapid recovery)
� Category C - buildings not assigned to the other categories (the default)
� Category D - less important buildings
For category A buildings, a site-specific hazard assessment (?) should be carried out, and in
fortification intensity zones 6 to 8, the seismic measures should be one grade higher than that of the
local intensity. For zones above 8 the measures should be appropriately higher.
For category B buildings, seismic measures for one grade higher should be applied in zones 6 to 8.
For zones above that the measures should be appropriately higher.
For category C buildings the measures appropriate to the local intensity should be applied.
For category D buildings, the seismic forces should comply with the local intensity zone, but the
seismic measures shall be appropriately lower (but not lower than 6).
Note that the category assignment also affects the foundation design (see section 3.3).
Site Classification
The ground conditions are defined in Chapter 4 ("Site, Subsoil and Foundation"). An equivalent
shear-wave velocity (vse) must be determined, which is defined as a weighted combination of the
shear velocity values (vs) of the underlying strata.
Site Classification (Table 4.1.6)
Overlaying thickness of soil profile
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Characteristic Period
The characteristic period is the site period (Tg) which depends on the site soil classification and upon
the design group, which is defined in Appendix A. If the soil is poor, it is likely to be type III or IV.
Note that this value should be increased by 0.05secs for rare earthqukes with intensity 8 or 9
Seismic Influences (seismic zone coefficients)
Section 3.2 - this refers to the local seismic hazard. Fortification Intensity is the basic design
intensity for design to the level 2 performance objective and is taken from maps or from the tables
that list major cities (Appendix A). Note that the code spectrum is not a uniform hazard spectrum.
The maximum values of spectral acceleration for the design response spectra are defined in the
following table.
Equivalent shear-wave velocity
(m/s)
(m)
(measured from bedrock to surface?)
vse > 500
Firm soil or rock
0
500≥vse>250
Medium firm soil
< 5 ≥ 5
250≥vse>140
Medium soft soil
< 3 3 - 50 > 50
vse≤140
Soft soil
< 3 3 - 15 > 15 - 80 > 80
Resulting Site Classification I II III IV
Characteristic period, Tg (sec)
Design Earthquake Group
(from Appendix A)
Site Class
I II III IV
Group 1 0.25 0.35 0.45 0.65
Group 2 0.30 0.40 0.55 0.75
Group 3 0.35 0.45 0.65 0.90
Max value of horizontal seismic influence coefficient - alpha_max (Combined Tables
3.2.2 & 5.1.4-1)
Earthquake Influence
Fortification Intensity (seismic zone)
6 7 7.5 8 8.5 9
Frequent Earthquake (level 1) 0.04 0.08 0.12 0.16 0.24 0.32
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For the sake of this combined table it has been assumed that the maximum coefficient (for 5%
damping) for the reference earthquake is equal to the ground acceleration divided by 0.45. The
reference PGA values (level 2) are given at the bottom of the table.
For linear (level 1) assessment, the frequent earthquake values for alpha-max should be used. A load
factor of 1.3 is specified for design combinations that include seismic load. Compliance with
performance under the level 2 earthquake is assumed to be met if the other performance levels are
assessed.
Design Response Spectrum
The peak of the design spectrum is the relevant value of alpha_max from the table above, modified
to account for the level of structural damping. In general 5% damping is assumed, under which case
the modification factor for the plateau force (eta_2) is unity. The start of the plateau is assumed to be
at 0.1 seconds, and the end of the plateau is at Tg. The spectrum is not defined beyond 6.0 seconds at
which point specialist assessments should be made. For 5% damping the velocity coefficient (eta_1)
is 0.2, and the resulting curve between Tg and 5Tg is defined by αmax * (T/Tg)0.9.
Reference earthquake (level 2) 0.11 0.22 0.33 0.44 0.67 0.89
Rare Earthquake (level 3) - 0.50 0.72 0.90 1.20 1.40
Design basic ground acceleration (g) 0.05 0.10 0.15 0.20 0.30 0.40
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Seismic Coefficient Graph - Design Basic Acceleration of Ground Motion
Seismic Detailing Requirements
For concrete buildings (chapter 6) there are four "grades" of detailing, which are defined according
to structural height and form and depend upon the site fortification intensity, and which result in
different calculations and design details (see Table 6.1.2). This affects a number of items including,
for example, the "strong column - weak beam" factor.
For masonry buildings (chapter 7) and steel buildings (chapter 8), detailing requirements are based
on the number of storeys and the fortification intensity.
For site class I (typically rock sites), the seismic detail requirements may be taken as follows (section
3.3.2):
� Importance Category A or B - as per zone intensity
� Importance Category C - as per one intensity level lower than the zone intensity (but not less
than 6)
Structural Regularity
Section 3.4.1 states that, "The architectural design shall be made in accordance with the requirements
of seismic conept design of buildings, a seriously irregular design scheme of building shall not be
adopted." The conditions are laid out in the sections following 3.4.1 and are roughly equivalent to
those from other seismic codes.
Analysis Methods
Analyses are only required for the level 1 earthquake and under certain conditions for the level 3
earthquake. No analysis at level 2 is required.
Basic Ground Acceleration for Selected Cities
City Group Intensity Level Design Ground Motion
Beijing 1 8 0.20g
Shanghai 1 7 0.10g
Chengdu 1 7 0.10g
Guangzhou 1 7 0.10g
Shenzhen 1 7 0.10g
Hong Kong 1 7 0.15g
Earthquake
Level
Analysis
Method Comments
Frequent
(section 5.1.2)
Base shear
method
May be used for simple regular structures with
uniform distribution of mass and stiffness in
elevation.
Response
spectrum
For fairly regular buildings that do not meet the
criteria for the base shear method.
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Load Combinations
When calculating the building mass for seismic analysis, some prorpotion of certain live loads
(variable loads) should be considered (as per the table below). Section 5.1.3 - When calculating
seismic forces, "the representative value of gravity load of the building shall be taken as the sum of
characteristic values of the weight of the structure and members plus the combination values of
variable loads on the structure. The combination coefficients for different variable loads shall be
taken from Table 5.1.3."
Note: "When the hanging weight of crane with hard hooks is bigger, the combination coefficient
shall be adopted according to the actual condition" (?)
For seismic load combinations see section 5.4.1.
Note that for the seismic load combinations, the load-bearing capacity of structural members may be
increased by dividing by the gamma_RE coefficients (see Table 5.4.2) - between 0.75 and 1.0.
Macau
The last line on page 158 refers to Macau which in Chinese seismicity terms is in zone 7 equivalent
to between UBC zone 1 and zone 2A. The 475 year return period event has a peak ground
acceleration of 0.1g, in Group 1 (group refers to the magnitude-distance bin which contributes most
of the hazard).
The Level 3 seismic force for the Macau area is:
Maximum spectral acceleration alfa max (Spectrum value at 0.2 sec) = 0.50g. This is in the 3rd row
of Table 5.1.4-1 Peak horizontal ground acceleration = 0.45x 0.50g = 0.225g.
analysis
Elastic time
history analysis
Required for those buildings in importance category
A, those having "extremely irregular configuration"
and those over the height limits in table 5.1.2-1.
Rare (section
5.5.2)
Non-linear time
thistory
analysis
Elasto-plastic deformation checks should be made
on buildings listed in section 5.5.2.
Live/Variable Load combination coefficients (Table 5.1.3)
Type of variable load Combination Coefficient
Snow load 0.5
Sand/dust load on roof 0.5
Roof live load not considered
Realistic (characteristic) live load 1.0
Floor live load (UDL) Library, Archives 0.8
Other civil buildings 0.5
Crane hanging load
Cranes with hard hooks 0.3
Cranes with flexible hooks not considered
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The 2,500 year PHGA to 500 year PHGA ratio is 0.225/0.10 = 2.25. For a low seismic zone, this
ratio is about correct. In a high seismic zone, this ratio is approximately 1.5.
Some notes on the specifics of a tall building design are given on the discussion page.
Table of Contents of Code
Chapter 1 General -- page 1
Chapter 2 Definitions and notations -- page 2
2.1 Definitions -- page 2
2.2 Main Notations -- page 3
Chapter 3 Basic requirements of seismic design -- page 5
3.1 Classifications of seismic fortification and corresponding criterion -- page 5
3.2 Seismic influences -- page 6
3.3 Site and subsoil -- page 6
3.4 Regularity of architectural design and structural design -- page 7
3.5 Structure system -- page 9
3.6 Structure analysis -- page 10
3.7 Nonstructural components -- page 11
3.8 Seismically isolation and energy-dissipating design -- page 12
3.9 Structural materials and construction -- page 12
3.10 Seismic response observation system of buildings -- page 14
Chapter 4 Site, Subsoil and Foundation -- page 15
4.1 Site -- page 15
4.2 Natural subsoil and foundations -- page 18
4.3 Liquefaction and soft subsoil -- page 19
4.4 Pile foundation -- page 24
Chapter 5 Seismic action and seismic checking for structures -- page 27
5.1 General -- page 27
5.2 Calculation of horizontal seismic action -- page 31
5.3 Calculation of vertical seismic action -- page 36
5.4 Seismic check for load-bearing capacity of structural members -- page 37
5.5 Seismic check for deformation -- page 38
Chapter 6 Multi-story and tall reinforced concrete buildings -- page 42
6.1 General -- page 42
6.2 Essentials in calculation -- page 47
6.3 Details of seismic design for framed structures -- page 53
6.4 Details of seismic design for the wall structures -- page 58
6.5 Details of seismic design for frame-wall structures -- page 61
6.6 Seismic design requirements for slab-column-wall structures -- page 62
6.7 Seismic design requirements for tube structures -- page 63
Chapter 7 Multi-story Masonry Buildings and Multi-story Brick Buildings with Bottom-frame or
Inner-frame -- page 65
7.1 General -- page 65
7.2 Essentials in calculation -- page 69
7.3 Details of seismic design for multi-story clay brick buildings -- page 74
7.4 Details of seismic design for multi-story small-block buildings -- page 80
7.5 Details of seismic design for multi-story buildings with bottom-frame -- page 82
7.6 Details of seismic design for multi-story buildings with inner-frames -- page 84
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Chapter 8 Multi-story and tall steel structure buildings -- page 86
8.1 General -- page 86
8.2 Essentials in calculation -- page 88
8.3 Details of seismic design for steel framed structures -- page 94
8.4 Details of seismic design for steel frame-epicenter-braced structures -- page 97
8.5 Details of seismic design for steel frame-eccentric-braced structures -- page 99
Chapter 9 Single-story factory buildings -- page 102
9.1 single-story factory buildings with reinforced concrete columns -- page 102
9.2 single-story steel structure factory buildings -- page 112
9.3 single-story factory buildings with brick columns -- page 115
Chapter 10 Single-story spacious buildings -- page 120
10.1 General -- page 120
10.2 Essentials in calculation -- page 120
10.3 Details of seismic design -- page 121
Chapter 11 Earth, wood and stone houses -- page 123
11.1 Unfired earth houses in villages and towns -- page 123
11.2 Wood houses -- page 124
11.3 Stone buildings -- page 125
Chapter 12 Seismic-isolation and seismic-energy-dissipating design -- page 127
12.1 General -- page 127
12.2 Essentials in design of seismic-isolation buildings -- page 128
12.3 Essentials in design of seismic-energy-dissipated buildings -- page 134
Chapter 13 Nonstructural components -- page 138
13.1 General -- page 138
13.2 Basic requirements for calculation -- page 138
13.3 Basic seismic-measures for architectural nonstructural members -- page 141
13.4 Basic seismic-measures for the supports of mechanical and electrical devices -- page 144
Appendix A The fortification intensity, design basic accelerations of ground motion and design
earthquake groups of main cities and towns in China -- page 146
Appendix B Requirements for seismic design of high strength grades concrete structures -- page 164
Appendix C Seismic design requirements for prestressed concrete structures -- page 166
Appendix D Seismic check for the core zone of the frame joints -- page 168
Appendix E Seismic design requirements for the transition-stories -- page 172
Appendix F Seismic design for reinforced
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