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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.
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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 總 則
1.0.1 為統一各種材料的建筑結構可靠性設計的基本原則、基本要求和基本方法，使結構符合可持續發展的要求，并符合安全可靠、經濟合理、技術先進、確保質量的要求，制定本標準。
1.0.2本標準適用于整個結構、組成結構的構件以及地基基礎的設計；適用于結構施工階段和使用階段的設計；適用于既有結構的可靠性評定。既有結構的可靠性評定，可根據本標準附錄A的規定進行。
1.0.3本標準依據現行國家標準《工程結構可靠性設計統一標準》GB 50153的原則制定，是建筑結構可靠性設計的基本要求。
1.0.4建筑結構設計宜采用以概率理論為基礎、以分項系數表達的極限狀態設計方法；當缺乏統計資料時，建筑結構設計可根據可靠的工程經驗或必要的試驗研究進行，也可采用容許應力或單一安全系數等經驗方法進行。
1.0.5制定建筑結構荷載標準、各種材料的結構設計標準以及其他相關標準時，應符合本標準規定的基本準則，并應制定相應的具體規定。
1.0.6建筑結構設計除應符合本標準的規定外，尚應符合國家現行有關標準的規定。
2術語和符號
2.1 術 語
2.1.1 結構 structure
能承受作用并具有適當剛度的由各連接部件有機組合而成的系統。
2.1.2結構構件structural member
結構在物理上可以區分出的部件。
2.1.3結構體系 structural system
結構中的所有承重構件及其共同工作的方式。
2.1.4結構模型structural model
用于結構分析、設計等的理想化的結構體系。
2.1.5設計使用年限design service life
設計規定的結構或結構構件不需進行大修即可按預定目的使用的年限。
2.1.6設計狀況design situations
表征一定時段內實際情況的一組設計條件，設計應做到在該組條件下結構不超越有關的極限狀態。
2.1.7持久設計狀況persistent design situation
在結構使用過程中一定出現，且持續期很長的設計狀況，其持續期一般與設計使用年限為同一數量級。
2.1.8短暫設計狀況transient design situation
在結構施工和使用過程中出現概率較大，而與設計使用年限相比，其持續期很短的設計狀況。
2.1.9偶然設計狀況accidental design situation
在結構使用過程中出現概率很小，且持續期很短的設計狀況。
2.1.10地震設計狀況seismic design situation
結構遭受地震時的設計狀況。
2.1.11 荷載布置load arrangement
在結構設計中，對自由作用的位置、大小和方向的合理確定。
2.1.12荷載工況load case
為特定的驗證目的，一組同時考慮的固定可變作用、永久作用、自由作用的某種相容的荷載布置以及變形和幾何偏差。
2.1.13極限狀態limit states
整個結構或結構的一部分超過某一特定狀態就不能滿足設計規定的某一功能要求，此特定狀態為該功能的極限狀態。
2.1.14 承載能力極限狀態 ultimate limit states
對應于結構或結構構件達到最大承載力或不適于繼續承載的變形的狀態。
2.1.15 正常使用極限狀態 serviceability limit states
對應于結構或結構構件達到正常使用的某項規定限值的狀態。
2.1.16不可逆正常使用極限狀態 irreversible serviceability limit states
當產生超越正常使用要求的作用卸除后，該作用產生的后果不可恢復的正常使用極限狀態。
2.1.17 可逆正常使用極限狀態reversible serviceability limit states
當產生超越正常使用要求的作用卸除后，該作用產生的后果可以恢復的正常使用極限狀態。
2.1.18 耐久性極限狀態durability limit states
對應于結構或結構構件在環境影響下出現的劣化達到耐久性能的某項規定限值或標志的狀態。
2.1.19抗力 resistance
結構或結構構件承受作用效應和環境影響的能力。
2.1.20結構整體穩固性 structural integrity；structural ro-bustness
當發生火災、爆炸、撞擊或人為錯誤等偶然事件時，結構整體能保持穩固且不出現與起因不相稱的破壞后果的能力。
2.1.21關鍵構件key member；key element
結構承載能力極限狀態性能所依賴的結構構件。
2.1.22連續倒塌progressive collapse
初始的局部破壞，從構件到構件擴展，最終導致整個結構倒塌或與起因不相稱的一部分結構倒塌。
2.1.23可靠性 reliability
結構在規定的時間內，在規定的條件下，完成預定功能的能力。
2.1.24可靠度degree of reliability；reliability
結構在規定的時間內，在規定的條件下，完成預定功能的概率。
2.1.25失效概率pf probability of failure pf
結構不能完成預定功能的概率。
2.1.26可靠指標β reliability index β
度量結構可靠度的數值指標，可靠指標β為失效概率pf負的標準正態分布函數的反函數。
2.1.27基本變量 basic variable
代表物理量的一組規定的變量，用于表示作用和環境影響、材料和巖土的性能以及幾何參數的特征。
2.1.28功能函數performance function
關于基本變量的函數，該函數表征一種結構功能。
2.1.29概率分布probability distribution
隨機變量取值的統計規律，一般采用概率密度函數或概率分布函數表示。
2.1.30統計參數statistical parameter
在概率分布中用來表示隨機變量取值的平均水平和離散程度的數字特征。
2.1.31分位值fractile
與隨機變量概率分布函數的某一概率相應的值。
2.1.32名義值nominal value
用非統計方法確定的值。
2.1.33極限狀態法limit state method
不使結構超越某種規定的極限狀態的設計方法。
2.1.34容許應力法permissible stress method，allowable stress method
使結構或地基在作用標準值下產生的應力不超過規定的容許應力的設計方法。
2.1.35單一安全系數法 single safety factor method
使結構或地基的抗力標準值與作用標準值的效應之比不低于某一規定安全系數的設計方法。
2.1.36作用action
施加在結構上的集中力或分布力和引起結構外加變形或約束變形的原因。前者為直接作用，也稱為荷載；后者為間接作用。
2.1.37外加變形imposed deformations
結構在地震、不均勻沉降等因素作用下，邊界條件發生變化而產生的位移和變形。
2.1.38約束變形constrained deformations
結構在溫度變化、濕度變化及混凝土收縮等因素作用下，由于存在外部約束而產生的內部變形。
2.1.39作用效應effect of action
由作用引起的結構或結構構件的反應。
2.1.40單個作用single action
可認為與結構上的任何其他作用之間在時間和空間上為統計獨立的作用。
2.1.41 永久作用permanent action
在設計使用年限內始終存在且其量值變化與平均值相比可以忽略不計的作用；或其變化是單調的并趨于某個限值的作用。
2.1.42可變作用variable action
在設計使用年限內其量值隨時間變化，且其變化與平均值相比不可忽略不計的作用。
2.1.43偶然作用accidental action
在設計使用年限內不一定出現，而一旦出現其量值很大，且持續期很短的作用。
2.1.44地震作用seismic action
地震動對結構所產生的作用。
2.1.45土工作用 geotechnical action
由巖土、填方或地下水傳遞到結構上的作用。
2.1.46 固定作用 fixed action
在結構上具有固定空間分布的作用。當固定作用在結構某一點上的大小和方向確定后，該作用在整個結構上的作用即得以確定。
2.1.47 自由作用 free action
在結構上給定的范圍內具有任意空間分布的作用。
2.1.48靜態作用 static action
使結構產生的加速度可以忽略不計的作用。
2.1.49 動態作用dynamic action
使結構產生的加速度不可忽略不計的作用。
2.1.50有界作用 bounded action
具有不能被超越的且可確切或近似掌握界限值的作用。
2.1.51 無界作用 unbounded action
沒有明確界限值的作用。
2.1.52作用的標準值characteristic value of an action
作用的主要代表值。可根據對觀測數據的統計、作用的自然界限或工程經驗確定。
2.1.53設計基準期design reference period
為確定可變作用等取值而選用的時間參數。
2.1.54可變作用的組合值combination value of a variable ac-tion
使組合后的作用效應的超越概率與該作用單獨出現時其標準值作用效應的超越概率趨于一致的作用值；或組合后使結構具有規定可靠指標的作用值。可通過組合值系數對作用標準值的折減來表示。
2.1.55可變作用的頻遇值frequent value of a variable action
在設計基準期內被超越的總時間占設計基準期的比率較小的作用值；或被超越的頻率限制在規定頻率內的作用值?？赏ㄟ^頻遇值系數對作用標準值的折減來表示。
2.1.56可變作用的準永久值 quasi-permanent value of a vari-able action
在設計基準期內被超越的總時間占設計基準期的比率較大的作用值。可通過準永久值系數對作用標準值的折減來表示。
2.1.57 可變作用的伴隨值accompanying value of a variable action
在作用組合中，伴隨主導作用的可變作用值?？勺冏饔玫陌殡S值可以是組合值、頻遇值或準永久值。
2.1.58作用的代表值representative value of an action
極限狀態設計所采用的作用值。它可以是作用的標準值或可變作用的伴隨值。
2.1.59作用的設計值design value of an action
作用的代表值與作用分項系數的乘積。
2.1.60作用組合combination of actions；荷載組合load com-bination
在不同作用的同時影響下，為驗證某一極限狀態的結構可靠度而采用的一組作用設計值。
2.1.61 環境影響 environmental influence
環境對結構產生的各種機械的、物理的、化學的或生物的不利影響。環境影響會引起結構材料性能的劣化，降低結構的安全性或適用性，影響結構的耐久性。
2.1.62材料性能的標準值characteristic value of a material prop-erty
符合規定質量的材料性能概率分布的某一分位值或材料性能的名義值。
2.1.63材料性能的設計值design value of a material property
材料性能的標準值除以材料性能分項系數所得的值。
2.1.64幾何參數的標準值 characteristic value of a geomet-rical parameter
設計規定的幾何參數公稱值或幾何參數概率分布的某一分位值。
2.1.65幾何參數的設計值design value of a geometrical pa-rameter
幾何參數的標準值增加或減少一個幾何參數的附加量所得的值。
2.1.66結構分析structural analysis
確定結構上作用效應的過程或方法。
2.1.67一階線彈性分析first order linear-elastic analysis
基于線性應力-應變或彎矩-曲率關系，采用彈性理論分析方法對初始結構幾何形體進行的結構分析。
2.1.68二階線彈性分析second order linear-elastic analysis
基于線性應力-應變或彎矩-曲率關系，采用彈性理論分析方法對已變形結構幾何形體進行的結構分析。
2.1.69有重分布的一階或二階線彈性分析 first order or sec-ond order linear-elastic analysis with redistribution
結構設計中對內力進行調整的一階或二階線彈性分析，與給定的外部作用協調，不做明確的轉動能力計算的結構分析。
2.1.70一階非線性分析first order non-linear analysis
基于材料非線性變形特性對初始結構的幾何形體進行的結構分析。
2.1.71二階非線性分析second order non-linear analysis
基于材料非線性變形特性對已變形結構幾何形體進行的結構分析。
2.1.72一階或二階彈塑性分析 first order or second elasto-plastic analysis
基于線彈性階段和隨后的無硬化階段構成的彎矩-曲率關系的結構分析。
2.1.73剛性-塑性分析rigid plastic analysis
假定彎矩-曲率關系為無彈性變形和無硬化階段，采用極限分析理論對初始結構的幾何形體進行的直接確定其極限承載力的結構分析。
2.1.74 既有結構 existing structure
已經存在的各類建筑結構。
2.1.75評估使用年限assessed working life
可靠性評定所預估的既有結構在規定條件下的使用年限。
2.1.76荷載檢驗load testing
通過施加荷載評定結構或結構構件的性能或預測其承載力的試驗。
2.2 符 號
2.2.1大寫拉丁字母：
Ad——偶然作用的設計值；
C——設計對變形、裂縫等規定的相應限值；
Fd——作用的設計值；
Fr——作用的代表值；
Gk——永久作用的標準值；
P——預應力作用的有關代表值；
Qk——可變作用的標準值；
Rd——結構或結構構件抗力的設計值；
S——結構或結構構件的作用效應；
——偶然作用設計值的效應；
Sd——作用組合的效應設計值；
Sd,dst——不平衡作用效應的設計值；
Sd,stb——平衡作用效應的設計值；
——永久作用標準值的效應；
SP——預應力作用有關代表值的效應；
——可變作用標準值的效應；
T——設計基準期；
X——基本變量。
2.2.2小寫拉丁字母：
ad——幾何參數的設計值；
dk——幾何參數的標準值；
fd——材料性能的設計值；
fk——材料性能的標準值；
pf——結構構件失效概率的運算值。
2.2.3大寫希臘字母：
Δa——幾何參數的附加量。
2.2.4小寫希臘字母：
β——結構構件的可靠指標；
γ0——結構重要性系數；
γF——作用的分項系數；
γG——永久作用的分項系數；
γL——考慮結構設計使用年限的荷載調整系數；
γM——材料性能的分項系數；
γ0——可變作用的分項系數；
γP——預應力作用的分項系數；
ψc——作用的組合值系數；
ψf——作用的頻遇值系數；
ψq——作用的準永久值系數。
3 基本規定
3.1 基本要求
3.1.1結構的設計、施工和維護應使結構在規定的設計使用年限內以規定的可靠度滿足規定的各項功能要求。
3.1.2結構應滿足下列功能要求：
1 能承受在施工和使用期間可能出現的各種作用；
2保持良好的使用性能；
3具有足夠的耐久性能；
4 當發生火災時，在規定的時間內可保持足夠的承載力；
5 當發生爆炸、撞擊、人為錯誤等偶然事件時，結構能保持必要的整體穩固性，不出現與起因不相稱的破壞后果，防止出現結構的連續倒塌；結構的整體穩固性設計，可根據本標準附錄B的規定進行。
3.1.3結構設計時，應根據下列要求采取適當的措施，使結構不出現或少出現可能的損壞：
1避免、消除或減少結構可能受到的危害；
2 采用對可能受到的危害反應不敏感的結構類型；
3采用當單個構件或結構的有限部分被意外移除或結構出現可接受的局部損壞時，結構的其他部分仍能保存的結構類型；
4不宜采用無破壞預兆的結構體系；
5使結構具有整體穩固性。
3.1.4宜采取下列措施滿足對結構的基本要求：
1采用適當的材料；
2采用合理的設計和構造；
3對結構的設計、制作、施工和使用等制定相應的控制措施。
3.2安全等級和可靠度
3.2.1 建筑結構設計時，應根據結構破壞可能產生的后果，即危及人的生命、造成經濟損失、對社會或環境產生影響等的嚴重性，采用不同的安全等級。建筑結構安全等級的劃分應符合表3.2.1的規定。
表3.2.1 建筑結構的安全等級
安全等級 破壞后果
一級 很嚴重：對人的生命、經濟、社會或環境影響很大
二級 嚴重：對人的生命、經濟、社會或環境影響較大
三級 不嚴重：對人的生命、經濟、社會或環境影響較小
3.2.2建筑結構中各類結構構件的安全等級，宜與結構的安全等級相同，對其中部分結構構件的安全等級可進行調整，但不得低于三級。
3.2.3可靠度水平的設置應根據結構構件的安全等級、失效模式和經濟因素等確定。對結構的安全性、適用性和耐久性可采用不同的可靠度水平。
3.2.4 當有充分的統計數據時，結構構件的可靠度宜采用可靠指標β度量。結構構件設計時采用的可靠指標，可根據對現有結構構件的可靠度分析，并結合使用經驗和經濟因素等確定。
3.2.5各類結構構件的安全等級每相差一級，其可靠指標的取值宜相差0.5。
3.2.6結構構件持久設計狀況承載能力極限狀態設計的可靠指標，不應小于表3.2.6的規定。
表3.2.6結構構件的可靠指標β
破壞類型 安全等級
一級 二級 三級
延性破壞 3.7 3.2 2.7
脆性破壞 4.2 3.7 3.2
3.2.7結構構件持久設計狀況正常使用極限狀態設計的可靠指標，宜根據其可逆程度取0～1.5。
3.2.8結構構件持久設計狀況耐久性極限狀態設計的可靠指標，宜根據其可逆程度取1.0～2.0。
3.3設計使用年限和耐久性
3.3.1建筑結構的設計基準期應為50年。
3.3.2建筑結構設計時，應規定結構的設計使用年限。
3.3.3建筑結構的設計使用年限，應按表3.3.3采用。
表3.3.3建筑結構的設計使用年限
類別 設計使用年限(年)
臨時性建筑結構 5
易于替換的結構構件 25
普通房屋和構筑物 50
標志性建筑和特別重要的建筑結構 100
3.3.4建筑結構設計時應對環境影響進行評估，當結構所處的環境對其耐久性有較大影響日寸，應根據不同的環境類別采用相應的結構材料、設計構造、防護措施、施工質量要求等，并應制定結構在使用期間的定期檢修和維護制度，使結構在設計使用年限內不致因材料的劣化而影響其安全或正常使用。
3.3.5環境對結構耐久性的影響，可通過工程經驗、試驗研究、計算、檢驗或綜合分析等方法進行評估；耐久性極限狀態設計可根據本標準附錄C的規定進行。
3.3.6 環境類別的劃分和相應的設計、施工、使用及維護的要求等，應符合國家現行有關標準的規定。
3.4可靠性管理
3.4.1為保證建筑結構具有規定的可靠性水平，除應進行設計計算外，還應對結構的材料性能、施工質量、使用和維護進行相應的控制?？刂频木唧w措施，應符合本標準附錄D和有關的勘察、設計、施工及維護等標準的專門規定。
3.4.2建筑結構的設計必須由具有相應資格的技術人員承擔。
3.4.3建筑結構的設計應符合國家現行的有關荷載、抗震、地基基礎和各種材料結構設計標準的規定。
3.4.4建筑結構的設計應對結構可能受到的偶然作用、環境影響等采取必要的防護措施。
3.4.5對建筑結構所采用的材料及施工、制作過程應進行質量控制，并按國家現行有關標準的規定進行驗收。
3.4.6建筑結構應按設計規定的用途使用，并應定期檢查結構狀況，進行必要的維護和維修；當需變更使用用途時，應進行設計復核并采取相應的技術措施。
4極限狀態設計原則
4.1 極限狀態
4.1.1極限狀態可分為承載能力極限狀態、正常使用極限狀態和耐久性極限狀態。極限狀態應符合下列規定：
1 當結構或結構構件出現下列狀態之一時，應認定為超過了承載能力極限狀態：
1)結構構件或連接因超過材料強度而破壞，或因過度變形而不適于繼續承載；
2)整個結構或其一部分作為剛體失去平衡；
3)結構轉變為機動體系；
4)結構或結構構件喪失穩定；
5)結構因局部破壞而發生連續倒塌；
6)地基喪失承載力而破壞；
7)結構或結構構件的疲勞破壞。
2 當結構或結構構件出現下列狀態之一時，應認定為超過了正常使用極限狀態：
1)影響正常使用或外觀的變形；
2)影響正常使用的局部損壞；
3)影響正常使用的振動；
4)影響正常使用的其他特定狀態。
3 當結構或結構構件出現下列狀態之一時，應認定為超過了耐久性極限狀態：
1)影響承載能力和正常使用的材料性能劣化；
2)影響耐久性能的裂縫、變形、缺口、外觀、材料削弱等；
3)影響耐久性能的其他特定狀態。
4.1.2對結構的各種極限狀態，均應規定明確的標志或限值。
4.1.3結構設計時應對結構的不同極限狀態分別進行計算或驗算；當某一極限狀態的計算或驗算起控制作用時，可僅對該極限狀態進行計算或驗算。
4.2設計狀況
4.2.1 建筑結構設計應區分下列設計狀況：
1持久設計狀況，適用于結構使用時的正常情況；
2 短暫設計狀況，適用于結構出現的臨時情況，包括結構施工和維修時的情況等；
3偶然設計狀況，適用于結構出現的異常情況，包括結構遭受火災、爆炸、撞擊時的情況等；
4地震設計狀況，適用于結構遭受地震時的情況。
4.2.2對不同的設計狀況，應采用相應的結構體系、可靠度水平、基本變量和作用組合等進行建筑結構可靠性設計。
4.3極限狀態設計
4.3.1 對本標準第4.2.1條規定的四種建筑結構設計狀況，應分別進行下列極限狀態設計：
1 對四種設計狀況均應進行承載能力極限狀態設計；
2對持久設計狀況尚應進行正常使用極限狀態設計，并宜進行耐久性極限狀態設計；
3對短暫設計狀況和地震設計狀況可根據需要進行正常使用極限狀態設計；
4對偶然設計狀況可不進行正常使用極限狀態和耐久性極限狀態設計。
4.3.2進行承載能力極限狀態設計時，應根據不同的設計狀況采用下列作用組合：
1 對于持久設計狀況或短暫設計狀況，應采用作用的基本組合；
2對于偶然設計狀況，應采用作用的偶然組合；
3對于地震設計狀況，應采用作用的地震組合。
4.3.3進行正常使用極限狀態設計時，宜采用下列作用組合：
1對于不可逆正常使用極限狀態設計，宜采用作用的標準組合；
2 對于可逆正常使用極限狀態設計，宜采用作用的頻遇組合；
3對于長期效應是決定性因素的正常使用極限狀態設計，宜采用作用的準永久組合。
4.3.4對每一種作用組合，建筑結構的設計均應采用其最不利的效應設計值進行。
4.3.5結構的極限狀態可采用下列極限狀態方程描述：
g(X1，X2，…，Xn)=0 (4.3.5)
式中： g(·)——結構的功能函數；
Xi(i=1，2，…，n)——基本變量，指結構上的各種作用和環境影響、材料和巖土的性能及幾何參數等；在進行可靠度分析時，基本變量應作為隨機變量。
4.3.6結構按極限狀態設計應符合下列規定：
g(X1，X2，…，Xn)≥0 (4.3.6)
4.3.7 當采用結構的作用效應和結構的抗力作為綜合基本變量時，結構按極限狀態設計應符合下列規定：
R-S≥0 (4.3.7)
式中：R——結構的抗力；
S——結構的作用效應。
4.3.8結構構件的設計應以規定的可靠度滿足本標準第4.3.6或第4.3.7條的要求。
4.3.9結構構件宜根據規定的可靠指標，采用由作用的代表值、材料性能的標準值、幾何參數的標準值和各相應的分項系數構成的極限狀態設計表達式進行設計；有條件時也可根據本標準附錄E的規定，直接采用基于可靠指標的方法進行設計。
