Research On Seismic Behavior And Performance Design Method Of Fiber Reinforced Concrete Shear Walls

Shear wall structures have long been recognized as effective lateral force resisting systems under strong earthquake action,capable of affecting seismic performance to structures subjected to axial-flexure-shear interaction.With the purpose of enhancing the deformation capacity of reinforced concrete(RC)shear walls,and controlling the damage tolerance under complicated stress state,the fiber-reinforced concrete(FRC)with high strain-hardening behavior in tension is prepared by mixing high toughness reinforced fiber into cement mortar matrix.By substituting brittle ordinary concrete with a ductile FRC,the steel reinforcement and FRC are deforming compatibly in the inelastic deformation regime.Moreover,it is also significant to determine the seismic response of shear wall structures by studying on the seismic performance design approaches rationally.Consequently,based on the experimental and theoretical studies on seismic behavior of FRC shear walls,a displacement-based seismic design method was presented for the typical frame-shear wall structural system,and the nonlinear dynamic history response analysis was performed.Main contents and achievements of the dissertation are as follows:(1)A set of six shear wall specimens was designed and constructed,in which the FRC was applied to replace ordinary concrete as matrix in the critical locations of shear walls suffering inelastic deformation.Considering the aspects of compression buckling and tensile stress concentration of longitudinal reinforcement of shear walls under high axial load,an approach was developed to enhance the stability and deformation capacity of structural steel reinforcement by means of steel sleeves that were placed onto the reinforcing bars in the potential plastic region.The failure phenomenon,mechanisms and hysteretic property for the shear walls were investigated by the quasi-static cyclic tests of the cantilever shear wall specimens,and the main factors of influencing deformation capacity and energy dissipation capacity were discussed.The test results indicate that the proposed FRC shear walls have excellent damage tolerance and deformation capacity as compared with conventional RC specimens,and increasing strength and ductility of longitudinal reinforcement and using steel sleeves can lead to improved cyclic behavior and energy dissipation capacity.(2)Given the high strain-hardening behavior in tension of FRC and the effect of steel sleeves,experimental results of six FRC shear walls under high axial load were analyzed,and a simple calculation method for moment-curvature of the eccentrically compressed FRC shear walls was presented corresponding to the four damage states of walls,including cracking,yielding,peak and ultimate loading.The main factors of influencing the compressive bending behavior of shear walls at different states were discussed.It is shown that the proposed moment-curvature calculation method can be used to predict the load-deformation relationship of FRC shear walls accurately.(3)Using combined theoretical and experimental regression analysis methods,the results gained from quasi-static cyclic tests on six shear walls with FRC in bottom region were investigated.A set of simplified computational formula was presented to estimate the load-displacement skeleton curves of FRC shear wall,which considering the influencing factors such as axial load ratio,ratio of longitudinal reinforcement in boundary regions,confinement index of stirrup,mechanical properties of FRC and steel reinforcement,and steel sleeve.To evaluate the effect of loading history on performance degradation of FRC shear wall,a damage model was introduced based on the fitted results of cyclic loading test data.Also,the overall seismic behaviors including unloading stiffness of hysteresis loops and residual strength on descending branch of skeleton curve were assessed quantitatively by a proposed restoring force model and hysteresis rules.(4)To build an effective approach for the monotonic load-deformation response analysis of FRC shear walls,a modified fiber model is developed based on the uniaxial shear-flexure model(USFM),considering the mechanisms of axial-flexure-shear interaction and characteristic of high strain-hardening in tension behavior of FRC.Study results indicate that the proposed model can predict deformation capacity of FRC shear walls subjected to monotonic static load accurately with respect to simulating each displacement components clearly and considering coupling effect of shear and flexure.Effect of the material property difference of various concrete on seismic behavior of shear wall is simulated and reflected by the compression softening factor.And the high performance of FRC on both shear and compression resistance capacity is shown with visualized physical conception as well.(5)According to the multiple performance objectives including the Life Safety objective under moderate earthquake and the Collapse Prevention objective under rare earthquake,a displacement-based seismic design method was presented for the RC frame-shear wall structure.For each performance level,roof drift,interstory drift of the structure and plastic hinge rotation at the base of wall were selected as the primary performance parameters.An nominal yield displacement corresponding to the first mode of structure was estimated based on the equivalent single-degree-of-freedom(ESDOF)system,then the required maximum base shear force was determined by using Yield Point Spectra(YPS)considering the inelastic demand,which is formed by the acceleration response spectrum.A ten-story RC frame-shear wall structural model was taken as an example to demonstrate the design process of the method in detail.Furthermore,subsequent nonlinear dynamic analyses were performed using the program PERFORM-3D.The analysis results show that the proposed method is sufficiently accurate for design,and can be referred for the inelastic structural design within a certain range of building floors.(6)The typical model for a ten-story frame-shear wall structure with FRC in the inelastic deformation critical locations was created as an example of case.Structural nonlinear dynamic history response analysis was performed under rare earthquake with 2% probability of exceedance in 50 years,which was motivated under single-directional ground motions.The result shows that FRC can improve seismic behavior of model structure better as the increase of earthquake damage state.According to the proposed incremental dynamic analysis(IDA)method by FEMA P695,the selected twenty-two pairs of ground motion record were normalized and scaled.Then the structural failure probability under different ground motion intensity levels was obtained based on the seismic fragility function,which was on the limit-state of Collapse Prevention.