Research On Pounding Response Of LRB Base Isolation Structure Under Extremely Rare Earthquakes

Compared with the traditional seismic structure,the base-isolated structure can effectively reduce the seismic response of the superstructure,but the isolation layer will produce large horizontal deformation.The current seismic design code for building structures(GB50011-2010)stipulates that the width of the isolation joints around the isolation structure should not be less than 1.2 times the maximum horizontal displacement value of each isolation support under rare earthquakes and not less than 200 mm.With the introduction of extremely rare earthquakes,will the base isolation structure collide with the surrounding retaining wall due to excessive horizontal deformation of the isolation layer under the action of extremely rare earthquakes,and whether the base isolation structure that has collided still has good seismic performance is worthy of further study.In this paper,the improved Kelvin pounding analysis model and bilinear restoring force model are used to establish the equation of motion of the base isolation structure colliding with the surrounding retaining wall.The MATLAB software is used for nonlinear timehistory analysis.Using the method of superimposed wavelet function to adjust the 22 farfield vibrations recommended by ATC-63,the adjusted average acceleration response spectrum can be fitted to the acceleration response spectrum of extremely rare earthquakes.Based on the statistical results of the nonlinear time-history analysis of 22 ground motions,the pounding response of the base-isolated structure under extreme earthquakes is studied.The curves of the average ductility coefficient of the superstructure and the average shear strain of the isolation support with the mechanical performance parameters of the isolation structure are compared in the two cases of considering pounding and not considering pounding.It is found that the base isolation structure has a high probability of pounding with the surrounding retaining wall under the action of extremely rare earthquakes.The pounding limits the deformation of the isolation layer,but it exacerbates the dynamic response of the superstructure.When ensuring that the deformation of the isolation support does not exceed the deformation of the ultimate failure state,the probability of pounding should be minimized.The base isolation structure designed according to the fortification intensity still has good seismic performance in the event of a pounding,while the base isolation structure designed to reduce the fortification intensity is not as good as the base fixed structure.Comparing the variation curves of the average ductility coefficient of the superstructure and the average shear strain of the isolation support with the mechanical performance parameters of the isolated structure under different pounding parameters,the effect of the pounding parameters and the mechanical performance parameters of the isolated structure on the isolated structure in extremely rare earthquakes is studied.The results show that increasing the yield capacity of the superstructure or isolation system can reduce the pounding response of the superstructure,increasing the width of the isolation joint,increasing the yield capacity of the isolation system or the diameter of the isolation support can reduce the probability of pounding.