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In accordance with the requirements of MOHURD Notice on Printing and Distributing the Development and Revision Plan of Engineering Construction Standards and Specifications in 2015 (JIAN BIAO [2014] No. 189), this standard is revised by the drafting team through extensive investigation, careful summarization of practical experience, reference to relevant international standards and foreign advanced standards and on the basis of widely solicited opinions.
The main technical contents of this standard are as follows: 1. General Provisions; 2. Terms and Symbols; 3. Basic Requirements; 4. Principle of Limit State Design; 5. Actions on Structures and Environmental Influences; 6. Properties of Materials and Geotechnics and Geometrical Quantities; 7. Structural Analysis and Design Assisted by Testing; 8. Method of Partial Factors Design.
The main technical contents of the revision of this standard are as follows: 1. Comprehensive coordination with the Unified Standard for Reliability Design of Engineering Structures (GB 50153-2008); 2. Adjustment of the setting level of the safety degree of the building structure, increasing of the value of the partial factors of related functions; and for the basic combination of the action, canceling of the combined functions of the original standard that played a controlling role when the permanent load effect is dominant; 3. Addition of the seismic design status, and introduction of the design concept of "No damage in small earthquake, repairable in medium earthquake and no failure in great earthquake" to the seismic design of building structure; 4. Improvement of the requirements on reliability assessment of existing structures; 5. Addition of relevant regulations on the overall stability design of the structure; 6. Addition of relevant regulations on design of limit state of structure durability.
The provision printed in bold type in this standard are compulsory and must be enforced strictly.
The Ministry of Housing and Urban-Rural Development of the People's Republic of China is in charge of the administration of this standard and the explanation of the compulsory provisions; China Academy of Building Research is responsible for the explanation of specific technical contents. During the process of implementing this code, the relevant opinions and advices, whenever necessary, can be posted or passed on to China Academy of Building Research (Address: No.30, North 3rd Ring East Road, Beijing, 100013, China).
Chief development organizations of this standard: China Academy of Building Research
Participating development organizations: China Northeast Architecture Design and Research Institute Co., Ltd., Chongqing University, Central-South Architectural Design Institute Co., Ltd., China Southwest Architectural Design and Research Institute Co., Ltd.,
Dalian University of Technology, Zhejiang University and National Center for Quality Supervision and Test of Building Engineering
Chief drafting staff of this standard: Shi Zhihua, Xiao Congzhen, Chen Kai, Zhu Aiping, Liu Bin, Dai Guoxin, Xu Houjun, Yang Xuebing, Gong Jinxin, Jin Weiliang, Teng Yanjing, Luo Kaihai, Di Xiaotang and Bai Shengxiang
Chief reviewers of this standard: Lou Yu, LiuXila, Zhang Yongyi, Liu Qiongxiang, Zheng Wenzhong, Wu Ti, Wang Lijun, Li Yuanqi, Zhang Xinpei and Xue Huili
Contents
1 General Provisions 1
2 Terms and Symbols 1
2.1 Terms 1
2.2 Symbol 8
3 Basic Requirements 10
3.1 Basic Principles 10
3.2 Class of Safety and Reliability 11
3.3 Design Service Life and Durability 12
3.4 Reliability Management 13
4 Principle of Limit State Design 14
4.1 Limit States 14
4.2 Design Situations 15
4.3 Limit State Design 15
5 Actions on Structures and Environmental Influences 17
5.1 General Requirements 17
5.2 Actions on Structures 17
5.3 Environmental Influences 20
6 Properties of Materials and Geotechnics and Geometrical Quantities 20
6.1 Properties and Geotechnics of Materials 20
6.2 Geometrical Quantities 21
7 Structural Analysis and Design Assisted by Testing 22
7.1 General Requirements 22
7.2 Structural Modelling 22
7.3 Actions Modelling 22
7.4 Method of Structural Analysis 23
7.5 Design Assisted by Testing 23
8 Method of Partial Factors Design 24
8.1 General Requirements 24
8.2 Ultimate Limit States 25
8.3 Serviceability Limit States 29
Appendix A Assessment of Existing Structures 32
Appendix B Structural Integrity 39
Appendix C Design of Durability Limit States 42
Appendix D Quality Management 48
Appendix E Basis for Reliability and Method of Structural Reliability Design 50
Appendix F Design Assisted by Testing 57
Explanation of Wording in This Standard 61
List of Quoted Standards 62
Unified Standard for Reliability Design of Building Structures
1 General Provisions
1.0.1 This standard is formulated with a view to unify the basic principles, basic requirements and basic methods for the reliability design of building structures of various materials, to make the structures conform to the requirements of sustainable development, and to meet the requirements of safety and reliability, economy and rationality, advanced in techniques and quality assurance.
1.0.2 This standard is applicable to the design for entire structure, members of component, and ground and foundation, to the design at construction phase and use phase, and to the reliability assessment of existing structure. The reliability assessment of existing structures may be performed in accordance with the provisions of Appendix A of this standard.
1.0.3 This standard is formulated according to the principle of the current national standard Unified Standard for Reliability Design of Engineering Structures (GB 50153). It is the basic requirement for reliability design of building structures.
1.0.4 The method of limit state design based on probability theory and expressed by partial factors design shall be adopted in design of building structures. In the absence of statistical data, design of building structure can be based on reliable engineering experience or necessary experimental studies, or on empirical methods such as allowable stresses or single safety factors.
1.0.5 When formulating the load standard of building structure, the standard for design of building structures of various materials and other relevant standards, the basic criteria specified in this standard shall be complied with and the corresponding specific provisions shall be formulated.
1.0.6 In addition to this standard, the design of building structures shall also comply with those specified in the relevant current national standards.
2 Terms and Symbols
2.1 Terms
2.1.1 structure
system organically composed of connected parts that can withstand action and have appropriate stiffness
2.1.2 structural member
component whose structure is physically distinguishable.
2.1.3 structural system
all bearing members in the structure and the way they work together
2.1.4 structural model
ideal structural system for structural analysis, design, etc.
2.1.5 design service life
service life for intended purpose of the structures or structural components without being overhauled, as specified in design
2.1.6 design situations
a set of design conditions representing the actual situation in a certain period of time. The design shall be such that the structure does not exceed the relevant limit state
2.1.7 persistent design situation
a design situation that must appear in the process of use of structures, and the duration is very long, which is generally the same order of magnitude as the design service life
2.1.8 transient design situation
a design situation that with high occurrence probability in the process of construction and use of the structures, and the duration is short with respect to the design service life.
2.1.9 accidental design situation
a design situation that with low occurrence probability and the duration is very short
2.1.10 seismic design situation
a design situation of the structure under earthquake
2.1.11 load arrangement
reasonable determination of the position, size and direction of free action in the design of structures
2.1.12 load case
a certain compatible load arrangement, deformation and geometric deviation of a group of simultaneous fixed variable action, permanent action, free action for specific verification purposes
2.1.13 limit states
a certain functional requirements that the whole structure or part of it fails to meet the design requirements when exceeding specific state, such state is the limit state of this function
2.1.14 ultimate limit states
states corresponding to structures or structural members reaching the maximum load bearing capacity or not applicable to continuously bear the deformation
2.1.15 serviceability limit states
state corresponding to structures or structural members reaching certain specified limits of normal service
2.1.16 irreversible serviceability limit states
when the action beyond the normal use requirements is removed, the effect of the action can not be restored to the normal service limit state
2.1.17 reversible serviceability limit states
when the action beyond the normal use requirements is removed, the effect of the action can be restored to the normal service limit state
2.1.18 durability limit states
state corresponding to the deterioration of structures or structural members under the environmental influences to reach a specified limit or signof durability
2.1.19 resistance
ability of structures or structural members to withstand effects of action and environmental influences.
2.1.20 structural integrity; structural robustness
ability of structures as a whole to remain stable in the event of accidental events such as fire, explosion, impact, or human error, without damaging consequences disproportionate to the cause
2.1.21 key member; key element
structural member on which the ultimate state performance of structures bearing capacity depends
2.1.22 progressive collapse
initial local damage, spreading from member to member, eventually causes the entire structure to collapse or a portion of the structure to collapse out of proportion to the cause
2.1.23 reliability
structure capacity completing intended function under specified conditions within the specified time
2.1.24 degree of reliability; reliability
probability of structures completing intended function under specified conditions within the specified time.
2.1.25 probability of failure pf
probability that structures cannot completing intended function
2.1.26 reliability index β
numerical index that measures the reliability of structures. reliability index β is the inverse function of the standard normal distribution function with negative probability of failure pf
2.1.27 basic variable
a specified group of variables representing physical quantities and used to represent properties of actions and environmental influences, materials and geotechnics and geometrical quantities
2.1.28 performance function
function of basic variables, representing one type of structure performance
2.1.29 probability distribution
statistical pattern of random variable values, usually expressed by probability density function or probability distribution function
2.1.30 statistical parameter
digital characteristics representing the average level and dispersion degree of random variable values
2.1.31 fractile
value corresponding to some probability of the distribution function of random variables
2.1.32 nominal value
value determined by a nonstatistical method
2.1.33 limit state method
design method that does not cause structures to exceed a specified limit state
2.1.34 permissible stress method; allowable stress method
design method in which the stress of structures or foundation under standard values of action does not exceed the specified permissible stress
2.1.35 single safety factor method
design method in which the effect ratio between the standard value of resistance and the standard value of action of structures or foundation is not less than a specified safety factor
2.1.36 action
concentrated force or distributed force applied on structures and the cause of imposed or constrained deformations of structures. The former is direct action, also known as load; the latter is indirect action
2.1.37 imposed deformations
displacement and deformation of structures caused by the change of boundary conditions under the action of earthquake, uneven settlement and other factors
2.1.38 constrained deformations
internal deformation of structures due to external constraints caused by the influence of temperature change, humidity change and concrete shrinkage
2.1.39 effect of action
reaction of structures or structural members caused by actions
2.1.40 single action
function can be considered statistically independent in time and space from any other actions on the structure
2.1.41 permanent action
action always exists in the design service life and the change of its quantity value is negligible in contrast to the average value; or action with its variation is monotonous and tends to a limit
2.1.42 variable action
action of which the value varies with time during the design service life and of which the variation is non-negligible in contrast to the average value
2.1.43 accidental action
action that may not appear in the design service life, but once it appears, it has a large quantity and a short duration
2.1.44 seismic action
action of an earthquake on structures
2.1.45 geotechnical action
action transfer from geotechnical, fill, or groundwater to structures
2.1.46 fixed action
action has fixed spatial distribution on structures. When the magnitude and direction of the fixed action at a certain point of the structure are determined, the action on the whole structure can be determined
2.1.47 free action
action has arbitrary spatial distribution within a given range of structures
2.1.48 static action
action that acceleration generated by it on the structure can be negligible
2.1.49 dynamic action
action that acceleration generated by it on the structure can not be negligible
2.1.50 bounded action
action has definite or approximate mastery of the limit value that cannot be exceeded
2.1.51 unbounded action
action without clear boundary value
2.1.52 characteristic value of an action
main representative value of an action. It can be determined according to the statistics of observation data, natural limit of action or engineering experience
2.1.53 design reference period
time parameters chosen for value selection of changeable actions
2.1.54 combination value of a variable action
action value at which excessive probability of the combined effect of action in the design reference period is consistent with the corresponding probability of the action when appears only; or the action value of the reliable index which makes the structure have unified standard after combination. It can be expressed by the reduction of the characteristic value of an action by combination value factor
2.1.55 frequent value of a variable action
action value at which the excessive total period is only a small section of the design reference period in the design reference period; or the action value at which the excessive frequency is the specified value in the design reference period. It can be expressed by the reduction of the characteristic value of an action by frequent value factor
2.1.56 quasi-permanent value of a variable action
action value at which the excessive total period is one half of the design reference period in the design reference period. It can be expressed by the reduction of the characteristic value of an action by quasi-permanent value factor
2.1.57 accompanying value of a variable action
variable action value accompanying with a dominant action in an action combination. The accompanying value of a variable action may be combination value, frequent value or quasi-permanent value
2.1.58 representative value of an action
action value used in limit state design. It may be the characteristic value of an action or the accompanying value of a variable action
2.1.59 design value of an action
product of representative value of an action multiplied by the partial factor of action
2.1.60 combination of actions; load combination
a set of design values of an action used to verify the reliability of structure at limit state under the simultaneous influence of different actions
2.1.61 environmental influence
various mechanical, physical, chemical, or biological adverse influences of the environment on structures. Environmental influence may cause the deterioration of structural material property, reduce the safety or applicability of structures, and affect the durability of structures
2.1.62 characteristic value of a material property
a fractile of the probability distribution of material property that conforms to the specified quality or nominal value of material property
2.1.63 design value of a material property
value obtained by dividing the characteristic value of a material property by the partial factor of material property
2.1.64 characteristic value of a geometrical parameter
nominal value of geometrical parameter specified in the design or fractile of the probability distribution of geometrical parameter
2.1.65 design value of a geometrical parameter
value obtained by increasing or decreasing the additional value of a geometrical parameter on the base of characteristic value of a geometrical parameter
2.1.66 structural analysis
process or method of determining effect of action on structures
2.1.67 first order linear-elastic analysis
structural analysis of initial structural geometry is carried out by using elastic theory and based on the relationship between linear stress, strain or bending moment and curvature
2.1.68 second order linear-elastic analysis
structural analysis of deformed structural geometry is carried out by using elastic theory and based on the relationship between linear stress, strain or bending moment and curvature
2.1.69 first order or second order linear-elastic analysis with redistribution
structural analysis that carry out first or second order linear-elastic analysis for the adjustment of internal forces in structural design, which is in harmony with the given external action, and no clear calculation of the rotational capacity
2.1.70 first order non-linear analysis
structural analysis of initial structural geometry is carried out based on nonlinear deformation characteristics of materials
2.1.71 second order non-linear analysis
structural analysis of deformed structural geometry is carried out based on nonlinear deformation characteristics of materials
2.1.72 first order or second elastoplastic analysis
structural analysis of the moment-curvature relationship based on the linear elastic stage and the subsequent non-hardening stage
2.1.73 rigid plastic analysis
structural analysis that assuming the moment-curvature relationship is the stage of inelastic deformation and hardening, the ultimate bearing capacity of the geometry of initial structure is directly determined by limit analysis theory
2.1.74 existing structure
a variety of existing building structures
2.1.75 assessed working life
service life of an existing structure under specified conditions that estimated by reliability evaluation
2.1.76 load testing
A test to evaluate the properties of structures or structural members or to predict its bearing capacity by applying a load
2.2 Symbol
2.2.1 Capital Latin letters:
Ad — design value of accidental action;
C — corresponding limits specified by the design for deformation, crack, etc.;
Fd — design value of an action;
Fr — representative value of an action;
Gk — characteristic value of a permanent action;
P — relevant representative value of prestress action;
Qk — characteristic value of a variable action;
Rd — design value of resistance of structures or structural members;
S — effect of action of structures or structural members;
— effect of design value of accidental action;
Sd — design value of effect of combination of actions;
Sd,dst — design value of unbalanced effect of action;
Sd,stb — design value of balanced effect of action;
— effect of characteristic value of a permanent action;
SP — effect of representative value of a prestress action;
— effect of characteristic value of a variable action;
T — design reference period;
X — basic variable.
2.2.2 Lowercase Latin letters:
ad — design value of a geometrical parameter;
dk — characteristic value of a geometrical parameter;
fd — design value of a material property;
fk — characteristic value of a material property;
pf — calculated value of probability of failure of structural members.
2.2.3 Capital Greek letters:
Δa — additional quantities of geometrical parameters.
2.2.4 Lowercase Greek letters:
β — reliability index of structural members;
γ0 — importance coefficient of structures;
γF — partial factor of a action;
γG — partial factor of a permanent action;
γL — load adjustment factor in consideration of the design service life of structures;
γM — partial factor of a material property;
γ0 — partial factor of a variable action;
γP — partial factor of a prestress action;
ψc — factor of combination value of a action;
ψf — factor of frequent value of a action;
ψq — factor of quasi-permanent value of a action.
3 Basic Requirements
3.1 Basic Principles
3.1.1 The design, construction and maintenance of structures shall ensure that structures meets the specified functional requirements with the specified reliability within the specified design service life.
3.1.2 Structures shall meet the following functional requirements:
1 Able to withstand various functions that may occur during construction and service;
2 Maintain good service property;
3 Has sufficient durability;
4 In case of fire, sufficient bearing capacity can be maintained within the specified time;
5 When explosion, impact, human error and other accidental events occur, structures shall be able to maintain the necessary overall stability without damaging consequences disproportionate to the cause, and to prevent the continuous collapse of structures; The structural integrity may be designed in accordance with the provisions specified in Appendix B of this standard.
3.1.3 In the design of structures, appropriate measures shall be taken according to the following requirements to avoid or minimize possible damage to structures:
1 Avoid, eliminate or reduce possible damages to structures;
2 Use the structure type that is insensitive to the possible harm;
3 Use the structure type that can be preserved by the rest of the structure when a limited part of a single member or structure is accidentally removed or when acceptable partial damage occurs to the structure;
4 It is not suitable to use a structural system without damage warning;
5 Ensure the structural integrity of structures.
3.1.4 The following measures should be taken to meet the basic requirements of structures:
1 Use of appropriate materials;
2 Use of reasonable design and construction;
3 Development of corresponding control measures for the design, manufacture, construction and use of structures.
3.2 Class of Safety and Reliability
3.2.1 During the design of building structures, different classes of safety shall be adopted according to the possible consequences of structural damage, that is, the seriousness of endangering human life, causing economic losses, and having an impact on society or the environment. The division of classes of safety for building structures shall be in accordance with those specified in Table 3.2.1.
Table 3.2.1 Classes of safety for building structures
Class of safety Failure consequence
Class 1 Very serious: it has a great impact on people's life, economy, society or environment
Class 2 Serious: it has a more impact on people's life, economy, society or environment
Class 3 Not serious: it has a little impact on human life, economy, society or environment
3.2.2 The class of safety of all kinds of structural members in the building structures should be the same as that of the structures. The class of safety of partial structural members can be adjusted, but not lower than Class 3.
3.2.3 The class of reliability shall be set according to the class of safety, failure mode and economic factors of structural members. Different classes of reliability can be used for the safety, suitability and durability of structures.
3.2.4 When sufficient statistical data are available, reliability index β should be adopted for the reliability of structural members. The reliability index used in the design of structural members can be determined according to the reliability analysis of existing structural members, combined with the practical experience and economic factors.
3.2.5 For every class of safety of various structural members, the value of reliability index should be with a difference of 0.5.
3.2.6 The reliability index for the ultimate state design of bearing capacity of structural components in the permanent design condition shall not be less than those specified in Table 3.2.6.
Table 3.2.6 Reliability index β for structural members
Type of failure Class of safety
Class 1 Class 2 Class 3
Ductile failure 3.7 3.2 2.7
Brittle failure 4.2 3.7 3.2
3.2.7 The reliability index of normal service limit state design for the permanent design of structural members should be 0 to 1.5 according to their reversible degree.
3.2.8 The reliability index of durability limit state design for the permanent design of structural members should be 1.0 to 2.0 according to their reversible degree.
3.3 Design Service Life and Durability
3.3.1 The design reference period of building structures shall be 50 years.
3.3.2 During the design of building structures, the design service life shall be specified.
3.3.3 The design service life of building structures shall be in accordance with Table 3.3.3.
1 General Provisions
2 Terms and Symbols
2.1 Terms
2.2 Symbol
3 Basic Requirements
3.1 Basic Principles
3.2 Class of Safety and Reliability
3.3 Design Service Life and Durability
3.4 Reliability Management
4 Principle of Limit State Design
4.1 Limit States
4.2 Design Situations
4.3 Limit State Design
5 Actions on Structures and Environmental Influences
5.1 General Requirements
5.2 Actions on Structures
5.3 Environmental Influences
6 Properties of Materials and Geotechnics and Geometrical Quantities
6.1 Properties and Geotechnics of Materials
6.2 Geometrical Quantities
7 Structural Analysis and Design Assisted by Testing
7.1 General Requirements
7.2 Structural Modelling
7.3 Actions Modelling
7.4 Method of Structural Analysis
7.5 Design Assisted by Testing
8 Method of Partial Factors Design
8.1 General Requirements
8.2 Ultimate Limit States
8.3 Serviceability Limit States
Appendix A Assessment of Existing Structures
Appendix B Structural Integrity
Appendix C Design of Durability Limit States
Appendix D Quality Management
Appendix E Basis for Reliability and Method of Structural Reliability Design
Appendix F Design Assisted by Testing
Explanation of Wording in This Standard
List of Quoted Standards
1 总 则
1.0.1 为统一各种材料的建筑结构可靠性设计的基本原则、基本要求和基本方法，使结构符合可持续发展的要求，并符合安全可靠、经济合理、技术先进、确保质量的要求，制定本标准。
1.0.2本标准适用于整个结构、组成结构的构件以及地基基础的设计；适用于结构施工阶段和使用阶段的设计；适用于既有结构的可靠性评定。既有结构的可靠性评定，可根据本标准附录A的规定进行。
1.0.3本标准依据现行国家标准《工程结构可靠性设计统一标准》GB 50153的原则制定，是建筑结构可靠性设计的基本要求。
1.0.4建筑结构设计宜采用以概率理论为基础、以分项系数表达的极限状态设计方法；当缺乏统计资料时，建筑结构设计可根据可靠的工程经验或必要的试验研究进行，也可采用容许应力或单一安全系数等经验方法进行。
1.0.5制定建筑结构荷载标准、各种材料的结构设计标准以及其他相关标准时，应符合本标准规定的基本准则，并应制定相应的具体规定。
1.0.6建筑结构设计除应符合本标准的规定外，尚应符合国家现行有关标准的规定。
2术语和符号
2.1 术 语
2.1.1 结构 structure
能承受作用并具有适当刚度的由各连接部件有机组合而成的系统。
2.1.2结构构件structural member
结构在物理上可以区分出的部件。
2.1.3结构体系 structural system
结构中的所有承重构件及其共同工作的方式。
2.1.4结构模型structural model
用于结构分析、设计等的理想化的结构体系。
2.1.5设计使用年限design service life
设计规定的结构或结构构件不需进行大修即可按预定目的使用的年限。
2.1.6设计状况design situations
表征一定时段内实际情况的一组设计条件，设计应做到在该组条件下结构不超越有关的极限状态。
2.1.7持久设计状况persistent design situation
在结构使用过程中一定出现，且持续期很长的设计状况，其持续期一般与设计使用年限为同一数量级。
2.1.8短暂设计状况transient design situation
在结构施工和使用过程中出现概率较大，而与设计使用年限相比，其持续期很短的设计状况。
2.1.9偶然设计状况accidental design situation
在结构使用过程中出现概率很小，且持续期很短的设计状况。
2.1.10地震设计状况seismic design situation
结构遭受地震时的设计状况。
2.1.11 荷载布置load arrangement
在结构设计中，对自由作用的位置、大小和方向的合理确定。
2.1.12荷载工况load case
为特定的验证目的，一组同时考虑的固定可变作用、永久作用、自由作用的某种相容的荷载布置以及变形和几何偏差。
2.1.13极限状态limit states
整个结构或结构的一部分超过某一特定状态就不能满足设计规定的某一功能要求，此特定状态为该功能的极限状态。
2.1.14 承载能力极限状态 ultimate limit states
对应于结构或结构构件达到最大承载力或不适于继续承载的变形的状态。
2.1.15 正常使用极限状态 serviceability limit states
对应于结构或结构构件达到正常使用的某项规定限值的状态。
2.1.16不可逆正常使用极限状态 irreversible serviceability limit states
当产生超越正常使用要求的作用卸除后，该作用产生的后果不可恢复的正常使用极限状态。
2.1.17 可逆正常使用极限状态reversible serviceability limit states
当产生超越正常使用要求的作用卸除后，该作用产生的后果可以恢复的正常使用极限状态。
2.1.18 耐久性极限状态durability limit states
对应于结构或结构构件在环境影响下出现的劣化达到耐久性能的某项规定限值或标志的状态。
2.1.19抗力 resistance
结构或结构构件承受作用效应和环境影响的能力。
2.1.20结构整体稳固性 structural integrity；structural ro-bustness
当发生火灾、爆炸、撞击或人为错误等偶然事件时，结构整体能保持稳固且不出现与起因不相称的破坏后果的能力。
2.1.21关键构件key member；key element
结构承载能力极限状态性能所依赖的结构构件。
2.1.22连续倒塌progressive collapse
初始的局部破坏，从构件到构件扩展，最终导致整个结构倒塌或与起因不相称的一部分结构倒塌。
2.1.23可靠性 reliability
结构在规定的时间内，在规定的条件下，完成预定功能的能力。
2.1.24可靠度degree of reliability；reliability
结构在规定的时间内，在规定的条件下，完成预定功能的概率。
2.1.25失效概率pf probability of failure pf
结构不能完成预定功能的概率。
2.1.26可靠指标β reliability index β
度量结构可靠度的数值指标，可靠指标β为失效概率pf负的标准正态分布函数的反函数。
2.1.27基本变量 basic variable
代表物理量的一组规定的变量，用于表示作用和环境影响、材料和岩土的性能以及几何参数的特征。
2.1.28功能函数performance function
关于基本变量的函数，该函数表征一种结构功能。
2.1.29概率分布probability distribution
随机变量取值的统计规律，一般采用概率密度函数或概率分布函数表示。
2.1.30统计参数statistical parameter
在概率分布中用来表示随机变量取值的平均水平和离散程度的数字特征。
2.1.31分位值fractile
与随机变量概率分布函数的某一概率相应的值。
2.1.32名义值nominal value
用非统计方法确定的值。
2.1.33极限状态法limit state method
不使结构超越某种规定的极限状态的设计方法。
2.1.34容许应力法permissible stress method，allowable stress method
使结构或地基在作用标准值下产生的应力不超过规定的容许应力的设计方法。
2.1.35单一安全系数法 single safety factor method
使结构或地基的抗力标准值与作用标准值的效应之比不低于某一规定安全系数的设计方法。
2.1.36作用action
施加在结构上的集中力或分布力和引起结构外加变形或约束变形的原因。前者为直接作用，也称为荷载；后者为间接作用。
2.1.37外加变形imposed deformations
结构在地震、不均匀沉降等因素作用下，边界条件发生变化而产生的位移和变形。
2.1.38约束变形constrained deformations
结构在温度变化、湿度变化及混凝土收缩等因素作用下，由于存在外部约束而产生的内部变形。
2.1.39作用效应effect of action
由作用引起的结构或结构构件的反应。
2.1.40单个作用single action
可认为与结构上的任何其他作用之间在时间和空间上为统计独立的作用。
2.1.41 永久作用permanent action
在设计使用年限内始终存在且其量值变化与平均值相比可以忽略不计的作用；或其变化是单调的并趋于某个限值的作用。
2.1.42可变作用variable action
在设计使用年限内其量值随时间变化，且其变化与平均值相比不可忽略不计的作用。
2.1.43偶然作用accidental action
在设计使用年限内不一定出现，而一旦出现其量值很大，且持续期很短的作用。
2.1.44地震作用seismic action
地震动对结构所产生的作用。
2.1.45土工作用 geotechnical action
由岩土、填方或地下水传递到结构上的作用。
2.1.46 固定作用 fixed action
在结构上具有固定空间分布的作用。当固定作用在结构某一点上的大小和方向确定后，该作用在整个结构上的作用即得以确定。
2.1.47 自由作用 free action
在结构上给定的范围内具有任意空间分布的作用。
2.1.48静态作用 static action
使结构产生的加速度可以忽略不计的作用。
2.1.49 动态作用dynamic action
使结构产生的加速度不可忽略不计的作用。
2.1.50有界作用 bounded action
具有不能被超越的且可确切或近似掌握界限值的作用。
2.1.51 无界作用 unbounded action
没有明确界限值的作用。
2.1.52作用的标准值characteristic value of an action
作用的主要代表值。可根据对观测数据的统计、作用的自然界限或工程经验确定。
2.1.53设计基准期design reference period
为确定可变作用等取值而选用的时间参数。
2.1.54可变作用的组合值combination value of a variable ac-tion
使组合后的作用效应的超越概率与该作用单独出现时其标准值作用效应的超越概率趋于一致的作用值；或组合后使结构具有规定可靠指标的作用值。可通过组合值系数对作用标准值的折减来表示。
2.1.55可变作用的频遇值frequent value of a variable action
在设计基准期内被超越的总时间占设计基准期的比率较小的作用值；或被超越的频率限制在规定频率内的作用值。可通过频遇值系数对作用标准值的折减来表示。
2.1.56可变作用的准永久值 quasi-permanent value of a vari-able action
在设计基准期内被超越的总时间占设计基准期的比率较大的作用值。可通过准永久值系数对作用标准值的折减来表示。
2.1.57 可变作用的伴随值accompanying value of a variable action
在作用组合中，伴随主导作用的可变作用值。可变作用的伴随值可以是组合值、频遇值或准永久值。
2.1.58作用的代表值representative value of an action
极限状态设计所采用的作用值。它可以是作用的标准值或可变作用的伴随值。
2.1.59作用的设计值design value of an action
作用的代表值与作用分项系数的乘积。
2.1.60作用组合combination of actions；荷载组合load com-bination
在不同作用的同时影响下，为验证某一极限状态的结构可靠度而采用的一组作用设计值。
2.1.61 环境影响 environmental influence
环境对结构产生的各种机械的、物理的、化学的或生物的不利影响。环境影响会引起结构材料性能的劣化，降低结构的安全性或适用性，影响结构的耐久性。
2.1.62材料性能的标准值characteristic value of a material prop-erty
符合规定质量的材料性能概率分布的某一分位值或材料性能的名义值。
2.1.63材料性能的设计值design value of a material property
材料性能的标准值除以材料性能分项系数所得的值。
2.1.64几何参数的标准值 characteristic value of a geomet-rical parameter
设计规定的几何参数公称值或几何参数概率分布的某一分位值。
2.1.65几何参数的设计值design value of a geometrical pa-rameter
几何参数的标准值增加或减少一个几何参数的附加量所得的值。
2.1.66结构分析structural analysis
确定结构上作用效应的过程或方法。
2.1.67一阶线弹性分析first order linear-elastic analysis
基于线性应力-应变或弯矩-曲率关系，采用弹性理论分析方法对初始结构几何形体进行的结构分析。
2.1.68二阶线弹性分析second order linear-elastic analysis
基于线性应力-应变或弯矩-曲率关系，采用弹性理论分析方法对已变形结构几何形体进行的结构分析。
2.1.69有重分布的一阶或二阶线弹性分析 first order or sec-ond order linear-elastic analysis with redistribution
结构设计中对内力进行调整的一阶或二阶线弹性分析，与给定的外部作用协调，不做明确的转动能力计算的结构分析。
2.1.70一阶非线性分析first order non-linear analysis
基于材料非线性变形特性对初始结构的几何形体进行的结构分析。
2.1.71二阶非线性分析second order non-linear analysis
基于材料非线性变形特性对已变形结构几何形体进行的结构分析。
2.1.72一阶或二阶弹塑性分析 first order or second elasto-plastic analysis
基于线弹性阶段和随后的无硬化阶段构成的弯矩-曲率关系的结构分析。
2.1.73刚性-塑性分析rigid plastic analysis
假定弯矩-曲率关系为无弹性变形和无硬化阶段，采用极限分析理论对初始结构的几何形体进行的直接确定其极限承载力的结构分析。
2.1.74 既有结构 existing structure
已经存在的各类建筑结构。
2.1.75评估使用年限assessed working life
可靠性评定所预估的既有结构在规定条件下的使用年限。
2.1.76荷载检验load testing
通过施加荷载评定结构或结构构件的性能或预测其承载力的试验。
2.2 符 号
2.2.1大写拉丁字母：
Ad——偶然作用的设计值；
C——设计对变形、裂缝等规定的相应限值；
Fd——作用的设计值；
Fr——作用的代表值；
Gk——永久作用的标准值；
P——预应力作用的有关代表值；
Qk——可变作用的标准值；
Rd——结构或结构构件抗力的设计值；
S——结构或结构构件的作用效应；
——偶然作用设计值的效应；
Sd——作用组合的效应设计值；
Sd,dst——不平衡作用效应的设计值；
Sd,stb——平衡作用效应的设计值；
——永久作用标准值的效应；
SP——预应力作用有关代表值的效应；
——可变作用标准值的效应；
T——设计基准期；
X——基本变量。
2.2.2小写拉丁字母：
ad——几何参数的设计值；
dk——几何参数的标准值；
fd——材料性能的设计值；
fk——材料性能的标准值；
pf——结构构件失效概率的运算值。
2.2.3大写希腊字母：
Δa——几何参数的附加量。
2.2.4小写希腊字母：
β——结构构件的可靠指标；
γ0——结构重要性系数；
γF——作用的分项系数；
γG——永久作用的分项系数；
γL——考虑结构设计使用年限的荷载调整系数；
γM——材料性能的分项系数；
γ0——可变作用的分项系数；
γP——预应力作用的分项系数；
ψc——作用的组合值系数；
ψf——作用的频遇值系数；
ψq——作用的准永久值系数。
3 基本规定
3.1 基本要求
3.1.1结构的设计、施工和维护应使结构在规定的设计使用年限内以规定的可靠度满足规定的各项功能要求。
3.1.2结构应满足下列功能要求：
1 能承受在施工和使用期间可能出现的各种作用；
2保持良好的使用性能；
3具有足够的耐久性能；
4 当发生火灾时，在规定的时间内可保持足够的承载力；
5 当发生爆炸、撞击、人为错误等偶然事件时，结构能保持必要的整体稳固性，不出现与起因不相称的破坏后果，防止出现结构的连续倒塌；结构的整体稳固性设计，可根据本标准附录B的规定进行。
3.1.3结构设计时，应根据下列要求采取适当的措施，使结构不出现或少出现可能的损坏：
1避免、消除或减少结构可能受到的危害；
2 采用对可能受到的危害反应不敏感的结构类型；
3采用当单个构件或结构的有限部分被意外移除或结构出现可接受的局部损坏时，结构的其他部分仍能保存的结构类型；
4不宜采用无破坏预兆的结构体系；
5使结构具有整体稳固性。
3.1.4宜采取下列措施满足对结构的基本要求：
1采用适当的材料；
2采用合理的设计和构造；
3对结构的设计、制作、施工和使用等制定相应的控制措施。
3.2安全等级和可靠度
3.2.1 建筑结构设计时，应根据结构破坏可能产生的后果，即危及人的生命、造成经济损失、对社会或环境产生影响等的严重性，采用不同的安全等级。建筑结构安全等级的划分应符合表3.2.1的规定。
表3.2.1 建筑结构的安全等级
安全等级 破坏后果
一级 很严重：对人的生命、经济、社会或环境影响很大
二级 严重：对人的生命、经济、社会或环境影响较大
三级 不严重：对人的生命、经济、社会或环境影响较小
3.2.2建筑结构中各类结构构件的安全等级，宜与结构的安全等级相同，对其中部分结构构件的安全等级可进行调整，但不得低于三级。
3.2.3可靠度水平的设置应根据结构构件的安全等级、失效模式和经济因素等确定。对结构的安全性、适用性和耐久性可采用不同的可靠度水平。
3.2.4 当有充分的统计数据时，结构构件的可靠度宜采用可靠指标β度量。结构构件设计时采用的可靠指标，可根据对现有结构构件的可靠度分析，并结合使用经验和经济因素等确定。
3.2.5各类结构构件的安全等级每相差一级，其可靠指标的取值宜相差0.5。
3.2.6结构构件持久设计状况承载能力极限状态设计的可靠指标，不应小于表3.2.6的规定。
表3.2.6结构构件的可靠指标β
破坏类型 安全等级
一级 二级 三级
延性破坏 3.7 3.2 2.7
脆性破坏 4.2 3.7 3.2
3.2.7结构构件持久设计状况正常使用极限状态设计的可靠指标，宜根据其可逆程度取0～1.5。
3.2.8结构构件持久设计状况耐久性极限状态设计的可靠指标，宜根据其可逆程度取1.0～2.0。
3.3设计使用年限和耐久性
3.3.1建筑结构的设计基准期应为50年。
3.3.2建筑结构设计时，应规定结构的设计使用年限。
3.3.3建筑结构的设计使用年限，应按表3.3.3采用。
表3.3.3建筑结构的设计使用年限
类别 设计使用年限(年)
临时性建筑结构 5
易于替换的结构构件 25
普通房屋和构筑物 50
标志性建筑和特别重要的建筑结构 100
3.3.4建筑结构设计时应对环境影响进行评估，当结构所处的环境对其耐久性有较大影响日寸，应根据不同的环境类别采用相应的结构材料、设计构造、防护措施、施工质量要求等，并应制定结构在使用期间的定期检修和维护制度，使结构在设计使用年限内不致因材料的劣化而影响其安全或正常使用。
3.3.5环境对结构耐久性的影响，可通过工程经验、试验研究、计算、检验或综合分析等方法进行评估；耐久性极限状态设计可根据本标准附录C的规定进行。
3.3.6 环境类别的划分和相应的设计、施工、使用及维护的要求等，应符合国家现行有关标准的规定。
3.4可靠性管理
3.4.1为保证建筑结构具有规定的可靠性水平，除应进行设计计算外，还应对结构的材料性能、施工质量、使用和维护进行相应的控制。控制的具体措施，应符合本标准附录D和有关的勘察、设计、施工及维护等标准的专门规定。
3.4.2建筑结构的设计必须由具有相应资格的技术人员承担。
3.4.3建筑结构的设计应符合国家现行的有关荷载、抗震、地基基础和各种材料结构设计标准的规定。
3.4.4建筑结构的设计应对结构可能受到的偶然作用、环境影响等采取必要的防护措施。
3.4.5对建筑结构所采用的材料及施工、制作过程应进行质量控制，并按国家现行有关标准的规定进行验收。
3.4.6建筑结构应按设计规定的用途使用，并应定期检查结构状况，进行必要的维护和维修；当需变更使用用途时，应进行设计复核并采取相应的技术措施。
4极限状态设计原则
4.1 极限状态
4.1.1极限状态可分为承载能力极限状态、正常使用极限状态和耐久性极限状态。极限状态应符合下列规定：
1 当结构或结构构件出现下列状态之一时，应认定为超过了承载能力极限状态：
1)结构构件或连接因超过材料强度而破坏，或因过度变形而不适于继续承载；
2)整个结构或其一部分作为刚体失去平衡；
3)结构转变为机动体系；
4)结构或结构构件丧失稳定；
5)结构因局部破坏而发生连续倒塌；
6)地基丧失承载力而破坏；
7)结构或结构构件的疲劳破坏。
2 当结构或结构构件出现下列状态之一时，应认定为超过了正常使用极限状态：
1)影响正常使用或外观的变形；
2)影响正常使用的局部损坏；
3)影响正常使用的振动；
4)影响正常使用的其他特定状态。
3 当结构或结构构件出现下列状态之一时，应认定为超过了耐久性极限状态：
1)影响承载能力和正常使用的材料性能劣化；
2)影响耐久性能的裂缝、变形、缺口、外观、材料削弱等；
3)影响耐久性能的其他特定状态。
4.1.2对结构的各种极限状态，均应规定明确的标志或限值。
4.1.3结构设计时应对结构的不同极限状态分别进行计算或验算；当某一极限状态的计算或验算起控制作用时，可仅对该极限状态进行计算或验算。
4.2设计状况
4.2.1 建筑结构设计应区分下列设计状况：
1持久设计状况，适用于结构使用时的正常情况；
2 短暂设计状况，适用于结构出现的临时情况，包括结构施工和维修时的情况等；
3偶然设计状况，适用于结构出现的异常情况，包括结构遭受火灾、爆炸、撞击时的情况等；
4地震设计状况，适用于结构遭受地震时的情况。
4.2.2对不同的设计状况，应采用相应的结构体系、可靠度水平、基本变量和作用组合等进行建筑结构可靠性设计。
4.3极限状态设计
4.3.1 对本标准第4.2.1条规定的四种建筑结构设计状况，应分别进行下列极限状态设计：
1 对四种设计状况均应进行承载能力极限状态设计；
2对持久设计状况尚应进行正常使用极限状态设计，并宜进行耐久性极限状态设计；
3对短暂设计状况和地震设计状况可根据需要进行正常使用极限状态设计；
4对偶然设计状况可不进行正常使用极限状态和耐久性极限状态设计。
4.3.2进行承载能力极限状态设计时，应根据不同的设计状况采用下列作用组合：
1 对于持久设计状况或短暂设计状况，应采用作用的基本组合；
2对于偶然设计状况，应采用作用的偶然组合；
3对于地震设计状况，应采用作用的地震组合。
4.3.3进行正常使用极限状态设计时，宜采用下列作用组合：
1对于不可逆正常使用极限状态设计，宜采用作用的标准组合；
2 对于可逆正常使用极限状态设计，宜采用作用的频遇组合；
3对于长期效应是决定性因素的正常使用极限状态设计，宜采用作用的准永久组合。
4.3.4对每一种作用组合，建筑结构的设计均应采用其最不利的效应设计值进行。
4.3.5结构的极限状态可采用下列极限状态方程描述：
g(X1，X2，…，Xn)=0 (4.3.5)
式中： g(·)——结构的功能函数；
Xi(i=1，2，…，n)——基本变量，指结构上的各种作用和环境影响、材料和岩土的性能及几何参数等；在进行可靠度分析时，基本变量应作为随机变量。
4.3.6结构按极限状态设计应符合下列规定：
g(X1，X2，…，Xn)≥0 (4.3.6)
4.3.7 当采用结构的作用效应和结构的抗力作为综合基本变量时，结构按极限状态设计应符合下列规定：
R-S≥0 (4.3.7)
式中：R——结构的抗力；
S——结构的作用效应。
4.3.8结构构件的设计应以规定的可靠度满足本标准第4.3.6或第4.3.7条的要求。
4.3.9结构构件宜根据规定的可靠指标，采用由作用的代表值、材料性能的标准值、几何参数的标准值和各相应的分项系数构成的极限状态设计表达式进行设计；有条件时也可根据本标准附录E的规定，直接采用基于可靠指标的方法进行设计。
