Seismic Behavior And Elastoplastic Seismic Response Of Steel-concrete Composite Frames

In recent years, steel-concrete composite frame structures are widely used in practical engineering because of superior seismic behaviors.The composite frames have been tested by several strong earthquakes both at home and abroad. Although the research on seismic behaviors of composite component has been comparatively mature, the study of seismic behaviors and responses of composite frame systems is still lack of systematicity, espacially the research on composite frame system composed of concrete filled tubular column and composite beam. Furthermore, the specifications related to seismic design of steel-concrete composite structures have not provided corresponding seismic design method and construction measures of composite frame. Focusing on the domestic and foreign research situation, the theoretical analysis and test study on seismic behaviors and inelastic responses of steel-concrete composite frame are conducted in this paper. The main contents include:(1) The steel-concrete composite beam dynamic models were established considering coupling of both flexural and axial vibrations. The vibration equations are derived by using force equilibrium and deformation compatibility conditions. The corresponding programs were developed to calculate the natural frequecies and dynamic responses of composite beam under different loads. The effects of interface slip, relative transversal displacement and shear deformation on dynamic behaviors of composite beam were analyzed.(2) Based on the finite element model of partial interaction composite beam, the stiffness matrix of semi-rigidly connected composite beams considering interface slip was derived. Introducing the dimensionless quantities which were related to the connector shearing stiffness and the joint rotation stiffness, the influences of the interface slip and the semi-rigidly joint on dynamic characteristics and responses of composite frame were studied.(3) Taking the axial compression ratio, slenderness ratio and linear stiffness ratio as main parameters, eight full composite frames composed of concrete filled tubular column and composite beam were designed to conduct low-reversed cyclic loading test. The seismic behaviors such as failure mode, hysteretic curve, strength degradation, rigidity degeneration, ductility and energy dissipation were analyzed.(4) On the basis of results of low-reversed cyclic loading test and theoretical analysis of composite frame, the simplified skeleton curve and load-displacement hysteretic curve restoring force model were presented considering the effects of axial compression ratio, slenderness ratio and linear stiffness ratio. The model can reflect the main features of hysteretic behavior of composite frame. It is concise, convenient and practical.(5) The general simplified moment-curvature restoring force model of composite structure component was presented on the basis of the proposed load-displacement restoring force model. According to mechanical properties of full composite frame structure, the elasto-plastic time procedure analysis program EPSRCF was developed to calculate the elasto-plastic seismic responses and analysis yield mechanism of full composite frame. The theoretical results were compared and verified with test results.(6) By using the elasto-plastic seismic responses analysis program of composite frame EPSRCF, the influeces of various parameters such as shear connection degree of composite beam, steel ratio of column section, slenderness ratio, linear stiffness ratio and axial compression ratio on seismic behavior and elasto-platic seismic responses as well as yield mechanism of composite beam were studied. The rational design scopes of all parameters were provided.