Seismic Assessment Of Precast Concrete Frame Structure Considering Connection Performance Uncertainty

Precast concrete(PC)structure has been widely used in recent years in China.The current design philosophy in China aims to realize the requirement that the performance of PC structure should be equivalent to that of cast-in-place structure through proper details of design.However,due to the particular ways of construction,the connection performance is defficult to guarantee,and the larger performance uncertainty of the connection areas becomes a major concern.Nevertheless,there were rare researches on the seismic safety of PC structure considering the larger uncertainty of connection performance,as well as how to ensure the PC structure to meet the safety requirements through proper seismic design.In this dissertation,the PC frame structure was selected as the research object.Tests were carried out to analyze the influence of construction defects on the seismic performance of connection joint.A nonlinear finite element model considering the connection performance was established according to the test results.The seismic performance assessment of PC frame strucuture was made according to the seismic fragility analysis framework proposed in this dissertation,and the design modification method was suggested based on the requirements of structural anti-collapse performance under seismic hazard.The main work and achievements are summarized as follows:(1)Pseudo-static tests under reverse cyclic loads of the precast beam-column joints including typical defects were carried out,and the influences of defects on failure pattern,strength degradation,stiffness degradation and energy dissipation capacity were investigated.The test results provided foundation for the establishment of structure model and further quantitative analyses of the influence of connection deficiency on structural seismic performance.(2)A nonlinear finite element analysis(FEA)model considering the connection defects was established to describe the performance of precast beam-column joint.The FEA model considered bond stress-slip relationship of steel bars,mechanical property of the section with grout-filled sleeves,shear stress-shear strain relationship of the concrete in the core area,as well as geometrical and material nonlinearity,which were the key factors that affect the connection performance.The availability of the FEA model was verified by the test results.(3)A seismic fragility analysis framework,in which the uncertainties associated with both ground motion and structural performance were considered,was estabilished to realize the seismic performance assessment of the PC structure considering the uncertainty of connection.The point estimate method and Latin hypercube sampling method were used to solve the problem of high computational cost in Monte Carlo simulation.A fragility curve modification method was also developed to process the divergent data in fragility analysis.(4)Several index archetypes of PC frame structure were designed according to China's seismic design code.The limit values of structural overstrength factor were given according to the study on the relationship between structural overstrength and anti-collapse performance under seismic hazard.On the basis,the adjustment coefficients of design earthquake action were given for the design modification of PC frame structure.