Study On Seismic Behavior And Seismic Fragility Of Multi-aged RC Shear Wall Structure In The Offshore Atmospheric Environment

The shear wall is widely used in high-rise buildings due to its excellent lateral force resistance.Under the offshore atmospheric environment,the degradation of the seismic performance of RC shear walls will accrue,because of the corrosion of inner bars of shear walls caused by the chloride penetration with the increase of its service age.Therefore,it is essential to evaluate the seismic performance and fragility of multi-aged RC shear walls.Main research contents of this paper are as follows:(1)Twelve RC shear walls specimens,of which shear span ratios were larger than two,were subjected to accelerated salt-frog corrosion in the environmental chamber.After achieving predetermined corrosion degree,each specimen was tested using cyclic loading to investigate the seismic performance of corroded RC shear walls under the offshore atmospheric environment.The test results indicated that the seismic performance of RC shear walls,which was represented by the failure mode,load-carrying capacity,ductility and energy dissipation,was strongly affected by the corrosion level of longitudinal bars.Meanwhile,the deformation capacity of specimen could be improved by increasing lateral distributed reinforcement as well as shortening transverse reinforcement distance in embedded column.The rise of axial compression ratio would lead to the degradation of deformation capacity and energy dissipation capacity of the corroded RC shear wall.(2)Considering descent segment of four broken-line skeleton,the calculation formulas of skeleton’s characteristic values were obtained based on the experimental data of the corroded specimens.According to the principle of energy dissipation,the degradation of the strength and stiffness is considered by inducing the cyclic deterioration index.A two-broken-line model was used to simulate the variation of the unloading stiffness with proper consideration of pinch effect.Finally,the hysteretic macromodel(P-(35))of the corroded RC shear wall was established,which coincides well with the experimental hysteretic curves.Meanwhile,by using three broken-line skeleton without considering descent segment,the shear hysteretic model(P-?)of the corroded RC shear wall was established on the basis of Hysteretic Material model,and validated to match experimental shear hysteretic curves relatively well.(3)Numerical analysis was conducted on the corroded specimens to consider the corrosion effect by selecting fiber model considering shear effect,which was based on material degradation and hysteretic shear model of corroded RC shear wall.The numerical analysis on the corroded specimens was performed through different model parameters combination,and hysteretic curves obtained by Model 4 matched well with the experimental hysteretic curves.(4)Considering the uncertainty of the reinforcement corrosion,the mean value and variance of reinforcement corrosion penetration corresponding to different ages,concrete strength,and concrete cover thickness were determined.Based on the proposed hysteretic macromodel of corroded RC shear wall,the performance index limitation of RC shear wall specimens corresponding to different ages,axial compression ratios,shear span ratios was determined.Meanwhile,on the basis of numerical modeling method(Model 4),the fragility curves of corroded RC shear wall corresponding to different ages were obtained through pushover analysis by considering the uncertainty of material property as well as reinforcement corrosion penetration.(5)The representative shear wall was designed by introducing typical structure space which considers main parameters influencing the seismic performance.Based on the material degradation and the hysteretic model of corroded RC shear wall,the numerical model of representative structures was established.Selecting 22 seismic waves to analyze the seismic demand of representative structures,the uncertainty of seismic fragility model was quantified.According to the performance index limitation of corroded RC shear wall structures which was determined by fragility curves,the fragility curves of RC shear wall representative structures corresponding to different ages,layers,fortification intensity were obtained finally.