Seismic Behavior And Seismic Fragility Analysis Of Large-scale SRC Frame-bent Structures

Under the earthquake,the collapse or damage of buildings will cause huge casualties and economic losses.Especially when important lifeline projects such as nuclear power plants and thermal power plants are damaged by earthquakes,they will also cause serious consequences such as paralysis of urban functions,delay in post earthquake disaster relief and recovery,and social chaos.The frame structure of the main powerhouse on the conventional island of a large-scale power plant is the core structure of the power production of the power plant.Under the guidance of the national policy of“increasing the large and suppressing the small and improving the efficiency”,the structure of the main powerhouse has been continuously developed to large-scale.Due to the requirements of production process and equipment layout,the overall layout of the main powerhouse structure is irregular,the local structure is complex,the load transfer path is not clear,and the overall performance is poor.It belongs to an irregular and unfavorable structure for earthquake resistance.The traditional reinforced concrete structure can not meet the requirements of the“large capacity,high parameter”unit of the main powerhouse of the large-scale power plant.This paper is based on the world’s first fourth-generation nuclear power technology（China Huaneng Shidaowan demonstration project）-the main powerhouse structure of conventional island steam turbine of CAP1400 nuclear power plan.For various special-shaped joints in SRC frame-bent structure system,the method of combining experimental research,numerical simulation and theoretical analysis is used to study the stress characteristics and failure process of SRC special-shaped joints under the earthquake.In addition,the seismic response,torsional resistance and seismic fragility analysis of SRC frame-bent structure under multi-dimensional ground motion are analyzed.The main work of this paper is as follows:（1）The quasi-static tests of 15 SRC beam-column joints are introduced,and the parameters of SRC special-shaped joints are analyzed by numerical simulation on the basis of experimental research.The analysis results show that when the inclined angle of the leaning beam reaches 30°,the yield load of the specimen decreases by about 21%,and the peak load decreases by about 18%.With the increase of steel content,the bearing capacity,deformation and energy dissipation performance of SRC leaning beam-column exterior joints,SRC variable-column exterior joints and SRC special-shaped interior joints are significantly improved,and the increase is large.（2）The corresponding shear influence coefficientsζand the joint special-shaped coefficientsκ₁,κ₂,κ_c,κ_αaffected by the height difference between the left and right beams,the height change of the left and right beams,the height change of the upper and lower column sections and the inclination angle of the inclined beam are proposed respectively,and the calculation formulas of shear capacity of SRC special-shaped joints are given.In addition,for the seismic design of SRC interior joints of unequal height with abreast and interior joint of unequal height with dislocation,the construction design method at staggered floor is proposed.It is suggested that for unequal height with dislocation interior joint,two or three-limb L-shaped stiffeners can be set at the staggered floor to enhance the overall seismic performance of the structure.Among them,the minimum right-angle length of L-shaped stiffeners should be greater than 1.5?h₁.（3）Based on the dynamic characteristics test and pseudo-dynamic test of three-pin two-span SRC frame-bent substructures,the finite element models of the substructure and the prototype structure were established by ABAQUS.Then,the dynamic elasto-plastic analysis of the prototype structure under the action of 8-degree frequent earthquake,8-degree fortification earthquake and 9-degree rare earthquake is carried out considering the unidirectional and bidirectional input conditions,respectively.The analysis results show that the first vibration mode of the main workshop of SRC frame-bent structure is longitudinal translation,the second vibration mode is lateral translation,and the third vibration mode is torsion.The ratio of longitudinal and transverse periods of SRC frame-bent structure is 0.799,and the ratio of the period of third vibration mode to the period of first vibration mode of the structure is 0.734,indicating that the longitudinal stiffness and transverse stiffness of the structure are quite different,and the torsional stiffness of the structure is relatively large.（4）The calculation program for obtaining the torsional component of ground motion from the translational component of ground motion is compiled by MATLAB,and the rocking and torsional components corresponding to different ground motion records are obtained.The seismic response of the structure under multi-dimensional ground motion is studied by inputting the translational and torsional components of ground motion in X and Y directions simultaneously in ABAQUS.The results show that the torsional component of ground motion has great influence on the seismic performance of structures with uneven mass and stiffness distribution.When the structure is subjected to multi-dimensional earthquakes,the overall lateral displacement of the structure is greatly increased by about 20%compared with the bidirectional earthquake;compared with the bidirectional earthquake,the longitudinal displacement of the structure increases greatly,with the maximum of 28%.In addition,this paper proposes a new type of SRC frame-bent main building structure system with few walls by flexibly distributing shear walls in the traditional SRC frame-bent main building structure.The system shows good seismic performance under the action of multi-dimensional earthquake,fortification earthquake and rare earthquake.（5）15 natural ground motions were selected and the corresponding torsional components were obtained.The incremental dynamic analysis and seismic fragility analysis of the main workshop of SRC frame-bent structure under multi-dimensional ground motions were carried out.The results show that the seismic fragility curve corresponding to the serviceability limit state of the structure is steeper,indicating that the overall structure is extremely easy to exceed the serviceability limit state.Selecting PGA as the IM parameter,the incremental dynamic analysis（IDA）results of the structure of main factory building of the SRC frame bent have higher safety margins than when S_ais the IM parameter.