Standard No.:	GB 50068-2018
English Name:	Unified standard reliability design of building structures
Chinese Name:	建筑结构可靠性设计统一标准
Professional Classification:	GB    National Standard
Issued by:	MOHURD
Issued on:	2018-11-01
Implemented on:	2019-4-1
Status:	valid
Superseding:	GB 50068-2001 Unified Standard for Reliability Design of Building Structures
Language:	English
File Format:	PDF
Word Count:	27500 words
Price(USD):	680.0
Delivery:	via email in 1 business day

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. 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