Seismic Response Analysis Of Base Isolation Structure Considering Strength Degradation Of Lead Rubber Bearing

Traditional seismic resistance methods for building structures involve increasing the stiffness,strength,and ductility of the structure to withstand small earthquakes.However,in the event of a large earthquake,the structure needs to consume seismic energy through structural ductility destruction,resulting in permanent deformation and structural component damage.To avoid this type of damage,seismic isolation design must be used to reduce the seismic impact on building structures.Seismic isolation technology is a seismic-resistant design method for building structures that involves setting a seismic isolation layer between the Superstructure and the foundation.By utilizing the deformation and damage of the isolation layer,seismic energy can be consumed,reducing the energy transmitted to the upper structure and reducing the seismic response of the upper structure.Lead rubber bearings have become the most commonly used bearings for seismic isolation due to their excellent isolation effect and simple structureHowever,lead rubber isolation bearings can experience changes in mechanical properties due to the increase in internal lead core temperature under fast reciprocating cyclic loads.In traditional seismic response analysis of isolated structures,the mechanical property parameters of the bearings are usually described as fixed values,making it difficult to predict the response of isolated structures in real earthquakes.In this paper,exploratory research was conducted based on previous research to address this issue,and the main research content is as follows:.(1)Firstly,three lead rubber isolation bearings of different sizes(Diameters of 400 mm,500mm,and 600mm)were subjected to fast reciprocating shear tests and basic horizontal shear tests to investigate the time required for the mechanical property parameters of the three sizes of lead rubber isolation bearings to recover to the pre-test state after the fast reciprocating shear test.The results show that the time required for the mechanical property parameters to recover for the bearings with diameters of 400 mm and 500 mm is 15 minutes,while for the bearing with a diameter of 600 mm,it is 30 minutes.(2)By conducting fast reciprocating shear tests on the three different-sized lead rubber bearings,the study investigated the regular changes in the horizontal mechanical property parameters of the lead rubber isolation bearings under different shear strains and compression stresses.The test was carried out with a loading frequency of 0.33 Hz and 11 cycles.The results show that with the increase in loading cycles,the characteristic strength of the bearings continuously decreases.Compared with the second cycle of loading,the amplitude of the decrease in characteristic strength is 20% to 30% on the tenth cycle.When the compression stress increases from 4MPa to 10 MPa,the characteristic strength and hysteresis loop area of the bearing increase,and the increase is larger when the compression stress increases from 4MPa to 7MPa than when it increases from 7MPa to 10 MPa.Additionally,as the shear strain increases from 50% to 75%,the change in the characteristic strength of the bearing does not exceed 5%,but the change in the hysteresis loop area exceeds 50%.(3)In this paper,based on the generalized Bouc-Wen,the parameters were analyzed and optimized,and then the generalized Bouc-Wen model considering the effect of bearing strength degradation was derived.The value of strength degradation factor of bearing under different compressive stress was determined by genetic algorithm,and the relationship between compressive stress and strength degradation factor of three different size bearings was established.The value of the strength degradation factor was substituted into the Simulink simulation software to simulate the hysteresis curve corresponding to the test condition,and the simulation results were compared with the test results.The results show that the generalized Bouc-Wen model considering the degradation effect of bearing strength has high applicability.(4)Based on the generalized Bouc-Wen model considering the strength degradation effect of the bearing proposed in this paper,the seismic response of the isolated structure considering and not considering the strength degradation effect of the bearing under the action of long-term and long-period seismic waves was analyzed by using Simulink simulation software.The analysis includes the displacement of the isolation layer and the isoaltion layer displacement angle.The results shows that the peak displacement and interlayer displacement angle of the isolation layer are larger than those without considering the bearing strength degradation effect.With the increase of peak ground acceleration,the peak displacement and inter-story displacement angle of the isolation layer further increase,resulting in an increased risk of collapse of the superstructure.The value of the strength degradation factor has a great influence on the peak displacement and inter-story displacement angle of the isolation layer.The larger the value of the strength degradation factor,the more obvious the performance degradation of the isolation layer.