Research On Seismic Performance And Fragility Analysis For Steel―concrete Composite Structural Systems Dissertation Submitted To Tsinghua University In Partial Fulfillment Of The Requirement For The Degree Of Doctor Of Engineering By Liu Yangbing ( Civi

Steel-concrete composite structures have been developed rapidly and widely used in China. But most of steel-concrete composite structures of native and abroad have scarcely undergone a strong earthquake, and the research on the aseismic performance of this type of structure is not enough. Based on theoretical analysis and numerical simulation, aseismic performance and seismic fragility of steel-concrete composite structures are studied. The main achievements of this dissertation are as follows:(1) Based on experimental and theoretical research on concrete-filled square tubular (CFST) members, a method for quick determining the plastic interactive yield surface of CFST columns is developed through theoretical analysis and large number of parametric analyses. The trilinear moment-curvature curve of CFST columns and steel-concrete composite beams are amended and the 4 poly-line moment-curvature curve models are respectively suggested for elasto-plastic analysis of CFST columns and steel-concrete composite beams.(2) The seismic performance analysis of steel-concrete composite frame structures is performed. And the mechanical properties, deformation behaviors and damage states of the five different frame structures are compared systemically. Furthermore the design formula to make sure the strong column-weak beam mechanism of the composite beams - CFST columns frame are preliminarily put forward, which can offer some valuable references in design of composite frame structures.(3) A fragility analysis method of performance-based is given. And four ultimate damage states for the entire structure and interstory are defined. Based on the ultimate damage states, a method of solving the limited values of the four performance levels is put forward. Furthermore, seismic fragility analysis is carried out for two different steel-concrete composite frames to assess the seismic fragility of the two frames. The influence of seismic demand variation is discussed. And the difference and conversion between total probability and half probability method of seismic fragility analysis are studied.(4) Elasto-plastic seismic response and parameters influence analysis of composite frame-concrete core wall structures are studied. The effects of connection forms of frame outrigger beams and parameters such as sections of beams and columns, thickness of frame-core tube etc. on the deformation and mechanical behavior of structures are investigated. The seismic damage model and the variation law of deformation and frame shear force with the increasing of the earthquake action are probed into. The results given in this paper can be helpful to practical seismic design for composite frame-concrete core wall structures. At last, the results of pushover analysis and elastic-plastic time history analysis are compared. And the applicability of pushover analysis method is discussed.