Research On Seismic Performance Of New Resilient Composite Columns And Resilience Of Its Frame Structure

In China,current seismic target of building structures requires that they do not collapse under large earthquakes.However,in some major earthquake events in China,a large number of buildings suffered stronger earthquake action than their designed precautionary intensity and was damaged or collapsed,which induced huge loss of people’s lives and property.Because of the damage and residual displacement caused by strong nonlinear deformation,some un-collapsed buildings can not be repaired.The demolition and reconstruction after the earthquakes cause significant economic losses.Therefore,the building structure need s to have resilience,that is,it can maintain a certain level of function during the earthquakes and after the earthquakes can be repaired quickly,so as to reduce economic losses and ensure social stability.For frame structures,Most of the function loss results from the full development of plastic hinges at the column end.When the structural column has resilience,the residual deformation of the column is small and the column end can be repaired even after earthquakes.Thus,the function of the structure can be restored after the earthquakes.In this paper,two new types of resilient composite columns(referred to as new resilient columns)utilizing ultra-high performance concrete(UHPC)and steel strand were proposed to solve this problem.The following is the main research content.(1)This paper provided the literature review of resilient columns and the bonding performance between UHPC and steel strand.The detail ed compositions of proposed new resilient columns were introduced and their working mechanisms were demonstrated.Three columns including one steel strand concrete column and two new resilient columns were designed and and fabricated.(2)By quasi-static cyclic tests,the three original specimens were first tested to failure and retested after the repair.By comparing with a previously tested RC column,the seismic performance of the present columns was discussed in detail,including the hysteretic curve,stiffness degradation,residual deformation and hysteretic energy dissipation,the strain response and column curvature.(3)Based on OpenSees platform,the numerical model s of the test specimens were established,and simulation results were compared with the test results to verify the reliability of the modeling.The parameter study of the present columns(both the steel strand concrete column and two new resilient columns)was carried out.Subsequently,the bearing capacity skeleton curves of the columns under different axial compression ratio,shear-span ratio,configuration ratio of steel strands and prestress level of steel strands were analyzed.(4)The RC frames under different fortification intensities,steel strand concrete frame and the resilient frame with two new resilient columns were designed and modeled by OpenSees.The Pushover analysis was carried out to study the bearing capacity curve and plastic hinge distribution law.For each type of frame,twenty seismic waves were selected to conduct nonlinear dynamic time history analysis(referred to as time history analysis).The maximum displacement and residual displacement of each structural floor under each seismic action were obtained.The inter-story displacement response,the variation of the inter-story residual displacement and its ratio to the maximum displacementwith the maximum displacement were compared and analyzed.(5)The vulnerability of the frames was analyzed.The average resilience indexs of the frames under each damage state were calculated by Monte Carlo simulation.According to the full probability theory,the resu lts were combined to study the resilience index of the structure under the given ground motion intensity.Compared with the ordinary RC frame,the relative growth rate of the resilience index of the frames with the proposed new resilient columns was analyzed.The loss of each frame is evaluated by the total loss of the structure based on the loss corresponding to the member damage state.The calculation formula of resilience benefit index was proposed,and the use benefit of resilient frames relative to ordinary RC frames was studied through the loss probability evaluation method during service period.