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Structural Engineers – Code for Loads on Building Structures 1. General Provisions 1.0.1 This code is formulated to meet the requirements of building structure design, ensuring safety, suitability, and economic rationality. 1.0.2 These specifications apply to the structural design of building projects. 1.0.3 These specifications are formulated in accordance with the principles specified in the Unified Standard for Reliability Design of Building Structures (GB50068-2001). 1.0.4 The actions involved in building structure design include direct actions (loads) and indirect actions (such as those caused by foundation deformation, concrete shrinkage, welding deformation, temperature changes, or earthquakes). These specifications only address the relevant loads. 1.0.5 The design base period adopted in this specification is 50 years. 1.0.6 The actions or loads involved in the design of building structures shall, in addition to complying with the provisions of this code, also meet the requirements of other current **standards. 2. Terminology and Symbols 2.1 Terms 2.1.1 Permanent load A load whose value does not change over time during the structure’s service life, or whose variation is negligible compared to the average value, or whose variation is monotonic and tends toward a limit value. 2.1.2 Variable load: A load whose value changes over time during the service life of a structure, and whose variation is not negligible compared to the average value. 2.1.3 Accidental load: A load that does not necessarily occur during the service life of a structure; when it does occur, its magnitude is high and its duration is short. 2.1.4 Representative values of a load: The load values used in design to verify the limit states, such as standard values, combined values, frequent occurrence values, and quasi-permanent values. 2.1.5 Design reference period: A time parameter selected to determine the representative values of variable loads. 2.1.6 Characteristic value/nominal value: The basic representative value of the load, which is the characteristic value of the statistical distribution of the maximum loads during the design base period (such as the mean, mode, median, or a certain percentile). 2.1.7 Combination value: For variable loads, it is the load value that enables the probability of the combined load effect exceeding a certain threshold during the design base period to be similar to the corresponding probability when that load acts alone ； Or load values that enable the combined structure to have reliably specified performance indicators. 2.1.8 Frequent value: For variable loads, it refers to the load value for which the total time of occurrence during the design base period exceeds a specified small ratio, or whose occurrence frequency is at a specified level. 2.1.9 Quasi-permanent value: For variable loads, it is the load value whose total duration of occurrence during the design base period is approximately half of that period. 2.1.10 Design value of a load: The product of the representative value of the load and the load partial factor. 2.1.11 Load effect: The response of a structure or its components caused by loads, such as internal forces, deformations, and cracks. 2.1.12 Load combination: In design based on limit states, it refers to the specified design values for various loads that occur simultaneously, in order to ensure the reliability of the structure. 2.1.13 Fundamental combination: The combination of permanent and variable actions used in the calculation of the ultimate bearing capacity. 2.1.14 Accidental combination: In the calculation of the ultimate limit state of bearing capacity, it refers to the combination of permanent actions, variable actions, and an accidental action. 2.1.15 Standard combination characteristic/nominal combination: When calculating under the service limit state, a combination of standard values or combined values is used as the representative value for the loads. 2.1.16 Frequent combinations When calculating the serviceability limit state, for variable loads, combinations using the frequent value or quasi-permanent value as the representative load value are adopted. 2.1.17 Quasi-permanent combinations: When calculating under the service limit state, quasi-permanent values are used as the representative values for variable loads. 2.1.18 Equivalent uniform live load: In structural design, for actual loads that are not distributed evenly on a floor, a uniform load is generally used as a substitute ； An equivalent uniformly distributed load refers to a uniformly distributed load whose load effect on the structure is consistent with that of the actual load. 2.1.19 Tributary area: The tributary area is used in the calculation of beams and columns; it refers to the floor area that bears the load of the component being calculated. It should be defined by the shear force zero line of the floor slab, and appropriate simplifications can be made in practical applications. 2.1.20 Dynamic coefficient: A coefficient used when designing structures or components that are subject to dynamic loads, based on static design principles; it is the ratio of the maximum dynamic effect on the structure or component to its corresponding static effect. 2.1.21 Basic snow load/reference snow pressure: The reference pressure for snow loads, which is generally determined by using observational data on the weight of snow covering open, flat areas in the vicinity, and by applying probability statistics to find the maximum value that occurs once every 50 years. 2.1.22 Basic wind pressure/reference wind pressure: The reference pressure for wind loads is determined by using the average wind speed over 10 minutes at a height of 10 m above an open, flat surface in the area in question. The maximum wind speed that occurs once every 50 years is identified through probabilistic statistics, and then, taking into account the corresponding air density, the wind pressure is calculated using equation (D.2.2-4). 2.1.23 Terrain roughness: A grade that describes the distribution of irregular obstacles on the ground over a 2 km area as the wind blows across it before reaching a structure. 2.2 Symbols Gk—Standard value of permanent loads ； Qk—standard value of variable load ； GGk—Standard value of the permanent load effect ； SQk—Standard value of the effect of variable loads ； S—Design value for load effect combination ； R—Design value of the resistance of structural members ； SA—Wind load effect in the windward direction ； SC—Effect of lateral wind load ； T—natural vibration period of the structure ； H—Height of the structure’s top ； B—Width of the windward face of the structure ； Re—Reynolds number ； St—Strouhal number ； Sk—Standard value of snow load ； So—basically snow load ； ωk—standard value of wind load ； ω0—basic wind pressure ； υcr—critical wind speed for lateral wind resonance ； α—Slope angle ； βz—Wind excitation coefficient at height z ； βgz—turbulence coefficient at height z ； γ0—structural importance coefficient ； γG—Factor for permanent loads ； γQ—sub-coefficient for variable loads ； ψc—combination factor for variable loads ； ψf—Frequency value coefficient for variable loads ； ψq—quasi-permanent value coefficient for variable loads ； μr—roof snow distribution coefficient ； μz—coefficient of variation with height for wind pressure ； μs—wind load capacity factor ； η—wind load topographic and geomorphic correction coefficient ； ξ—Coefficient of increase in wind load pulsation ； ν—Pulse impact coefficient of wind load ； φZ—structural mode shape coefficient ； ζ—structural damping ratio. 3. Load Classification and Load Effect Combinations 3.1 Load Classification and Representative Values of Loads 3.1.1 Loads acting on a structure can be divided into the following three categories: 1. Permanent loads, such as the structural weight, earth pressure, prestress, etc. 2. Variable loads, such as live loads on floors and roofs, snow load, crane loads, wind loads, snow loads, etc. 3. Accidental loads, such as explosive forces and impact forces. Note: Self-weight refers to the load generated by the weight of the material itself (gravity). 3.1.2 When designing building structures, different representative values should be used for various loads. For permanent loads, standard values shall be used as representative values. For variable loads, standard values, combined values, frequent occurrence values, or quasi-permanent values shall be used as representative values in accordance with the design requirements. The representative value of accidental loads shall be determined based on the characteristics of use of the building structure. 3.1.3 The standard value of permanent loads: for the structural self-weight, it can be determined by calculating based on the design dimensions of the structural members and the unit weight of the materials. For materials and components with large variations in self-weight (such as on-site manufactured insulation materials and thin-walled concrete components), the standard value of self-weight should be taken as either the upper or lower limit, depending on the unfavorable conditions for the structure. Note: For commonly used materials and components, reference can be made to Appendix A of this specification. 3.1.4 The standard values for variable loads shall be adopted in accordance with the provisions in the various chapters of this code. 3.1.5 When designing for the ultimate limit state of bearing capacity or the serviceability limit state using standard combination design, for variable loads, standard values or combined values shall be used as representative values in accordance with the combination provisions. The combined value of variable loads shall be the standard value of the variable loads multiplied by the load combination coefficient. 3.1.6 When designing for the normal service limit state using the frequent occurrence combination, the frequent occurrence values and quasi-permanent values shall be used as representative values for variable loads ； When designing for quasi-permanent combinations, quasi-permanent values should be used as representative values for variable loads. The frequent value of variable loads shall be taken as the standard value of variable loads multiplied by the frequent value coefficient. The quasi-permanent value of variable loads shall be taken as the standard value of variable loads multiplied by the quasi-permanent value coefficient. 3.2 Load Combinations 3.2.1 The design of building structures shall take into account the loads that may act on the structure simultaneously during its service life. Load (effect) combinations shall be established for both the limit state of serviceability and the limit state of ultimate strength, and the most unfavorable combination of effects for each case shall be used in the design. 3.2.2 For the ultimate limit state of bearing capacity, the loads (effects) shall be combined according to the basic or accidental combination of load effects, and the following design expression shall be used for design. Where γ0 is the structural importance factor ； S—Design value of the load effect combination ； R—the design value of the resistance of structural members shall be determined in accordance with the provisions of the relevant building structure design codes. 3.2.3 For basic combinations, the design value S of the load effect combination shall be determined by taking the most unfavorable value from the following combination values: 1) The combination controlled by variable load effects: wherein γG is the partial safety factor for permanent loads, which shall be adopted in accordance with Article 3.2.5 ； γQi—is the partial coefficient for the i-th variable load; γQ1 is the partial coefficient for the variable load Q1, which shall be determined in accordance with Article 3.2.5 ； SGK—Load effect value calculated based on the standard value of permanent load Gk ； SQik—is the value of the load effect calculated based on the standard value of the variable load Qik, where SQ1k represents the variable load effect that has a controlling influence ； ψci—is the coefficient for the combined value of the variable load Qi, which shall be applied in accordance with the provisions of respective chapters ； n—The number of variable loads involved in the combination. 2) Combinations controlled by the effect of permanent loads: Note: 1 The design values in the basic combinations are applicable only in cases where the loads and load effects are linear. 2 When it is not possible to make a clear judgment regarding SQ1k, each variable load effect is taken as SQ1k in turn, and the most unfavorable combination of load effects is selected. 3 When considering a combination controlled by the effect of vertical permanent loads, the variable loads involved in the combination are limited to vertical loads only. 3.2.4 For general shed and frame structures, simplified rules can be applied for the basic combinations, and the most unfavorable value among the following combination values shall be selected: 1) The combination controlled by the effects of variable loads; 2) The combination controlled by the effects of permanent loads shall still be determined using equation (3.2.3-2). 3.2.5 The load partial factors for basic combinations shall be applied in accordance with the following provisions: 1 Partial factor for permanent loads: 1) When their effect is adverse to the structure — For combinations controlled by the effects of variable loads, a value of 1.2 shall be used ； —For combinations controlled by the effect of permanent loads, 1.35 shall be adopted ； 2) When its effect is beneficial to the structure — In general, 1.0 should be used ； —For the checks regarding overturning, sliding, or floating of the structure, a value of 0.9 shall be used. 2 Coefficients for variable loads: —In general, a value of 1.4 shall be used ； —For industrial building floor structures with a standard value greater than 4 KN/m2, the live load should be taken as 1.3. Note: In some special cases, it may be determined in accordance with the relevant design codes for building structures. 3.2.6 For accidental combinations, the design values of the load effect combinations shall be determined in accordance with the following provisions: the representative value of accidental loads shall not be multiplied by a partial factor ； Other loads that occur simultaneously with accidental loads can be assigned appropriate representative values based on observational data and engineering experience. The formula for the design value of load effects under various conditions may be specified separately in relevant codes. 3.2.7 For the serviceability limit state, depending on the various design requirements, standard load combinations, frequent occurrence combinations, or quasi-permanent combinations shall be used, and the design shall be carried out in accordance with the following design equation: S ≤ C (3.2.7) Where C represents the specified limits that the structure or its components must meet in order to satisfy serviceability requirements; these limits relate to aspects such as deformation, cracks, amplitude, acceleration, stress, etc., and shall be determined in accordance with the provisions of the relevant building structure design codes. 3.2.8 For standard combinations, the design value S of the load effect combination shall be adopted according to the following formula: Note: The design values in the combinations are applicable only when the relationship between loads and load effects is linear. 3.2.9 For frequently occurring combinations, the design value S of the load effect combination shall be adopted according to the following formula: wherein Ψf1 is the coefficient for the frequently occurring value of the variable load Q1, which shall be taken in accordance with the provisions in the respective chapters ； ψqi—is the quasi-permanent value coefficient for the variable load Qi, which shall be adopted in accordance with the provisions of the respective chapters. Note: The design values in the combination are applicable only when the loads and load effects are linear. 3.2.10 For quasi-permanent combinations, the design value S of the load effect combination can be obtained using the following formula: Note: The design values in these combinations are applicable only when the relationship between loads and load effects is linear. Reposted from: Structural Engineer Exam_Exam