Calculation And Study Of Seismic Response Of A Bi-directional Nonlinear Isolation Layer System Considering The Superstructure Form

Base isolation technology is an emerging technology to resist earthquake,mainly by setting up isolation device and damping energy dissipation element in the isolation layer to reduce the influence of ground vibration on the superstructure,thus improving the safety of the building and ensuring the function of buildings.Due to the remarkable performance of the base-isolation structures in the actual earthquake and engineering experiments,it has attracted the attention of both scholars and engineers at domestic and abroad.Over the past four decades,the theory,experiment and design researchs of isolation technology have been deepening,perfecting and maturing.However,in the calculation of seismic response of isolated structures,the simplified calculation model and many assumptions are often used,and the seismic response factors that influence the structures are ignored.It is necessary to further improve and study the seismic response analysis theory and calculation method of base isolation technology to provide reliable,reasonable and practical calculation and analysis method for isolation structures.This article summarizes the common isolation bearing restoring force model,and improve and perfect,set up suitable for lead rubber bearing the two-way coupling nonlinear restoring force mode.The layer element model is used for the superstructure,and the dynamic analysis model of the isolated structure is established.By using the improved Wilson-θ numerical integration method,it can ensure the accuracy and convergence of the acceleration.And the corresponding calculation program for the dynamic response of base isolation structures is compiled.Taking the Benchmark model of isolated structure as the research object,this paper uses the nonlinear program and the equivalent linear model to compare the seismic response.There are some differences in the calculation results,in which the results of the equivalent linear model are small and insecure,that is more unfavorable to the design of the isolation structure.The force-displacement relationship between the lead rubber bearing and the high damping rubber bearing is a hysteresis loop,and the constitutive relationship is nonlinear.Therefore,it is necessary to appropriately consider the nonlinear restoring force characteristics of the isolation layer.At the same time,the error of the two methods is within a reasonable range,which verifies the reliability of the program.Compared with the non-linear seismic response analysis of one-way and two-way seismic isolation layers,there are differences in seismic responses such as displacement and acceleration in each layer,and there are large differences in the hysteresis curves of the isolation bearings.The results shows the necessity of adopting two-way seismic input.Earthquake response analysis has been performed on the model.The isolated structure models with frame shears and shear walls in the upper part of the structure are used as the research objects.The calculation program is compared with the commercial finite element software ETABS for seismic analysis.The calculation results further validate the reliability and applicability of the program.A detailed seismic response analysis has been performed on the two isolated structures.Compared with the non-isolated structure,the seismic response of the superstructure after the base isolation is significantly reduced,and more than 60% of the energy input by the earthquake to the seismic isolation structure is absorbed by the isolation layer.Isolation effect is remarkable.The internal forces of the upper structural members have been analyzed and compared.After the isolation,the internal forces of the upper structure are reduced to less than half of those without isolation.