Effect Of Seismic Wave Characteristics On Seismic Response Of Friction Seismic Isolation System

China is located between the two largest earthquake zones in the world.How to reduce earthquake damage is one of the main technical problems faced by bridge design.The friction pendulum bearing has become the main method for researchers to improve the mechanical behavior of bridges during earthquakes due to its good isolation effect and low economic cost.However,due to the nonlinear mechanism of friction,the seismic response of friction pendulum bearings may vary greatly even if it suffers from earthquakes that having the same response spectrum.Therefore,this paper takes the spring-friction single-degree-of-freedom system as the research object,and utilize the artificial wave synthesis to study the effect of seismic wave characteristics on the response of the friction isolation system.The main research work and results are as follows:(1)The basic mechanical principles and motion characteristics of the friction pendulum bearing during the earthquake are analyzed,and the mechanical behavior of the friction pendulum bearing is simulated by the spring-friction single-degree-of-freedom system.Then the dynamic time history analysis program of the friction single-degree-of-freedom system is written through MATLAB.The differences in seismic response of friction isolation systems were analyzed by scaling the peak acceleration(PGA)of Northridge wave to different magnitudes as seismic inputs.The calculation results show that with the increase of PGA,the maximum relative velocity and relative displacement of the structure increase significantly,which in turn will increase the spring force on the structure.However,since the maximum friction force is fixed,the maximum acceleration of the structure increases not obviously.(2)Due to the small number of natural seismic wave samples that meet the requirements and the large difference in response spectrum,this paper writes a program for synthesizing artificial waves by the traditional triangular series method.Shaking table tests usually filter the input seismic waves in advance to meet the requirements of the equipment,and the spectral characteristics of the seismic waves will be changed accordingly.High frequency(higher than 50Hz)and low frequency(lower than 0.1HZ)parts of the input seismic waves were filtered out by Fourier transform,and the effect of changing the spectral characteristics of the input seismic wave on the response of the friction isolation system was analyzed.The calculation results show that when the spring stiffness is small,the maximum acceleration error of the structure caused by filtering decreases with the increase of the friction coefficient.When the spring stiffness of the system is large,the maximum acceleration error of the structure caused by filtering first increases and then decreases with the increase of the friction coefficient because the acceleration response of the structure decreases first and then increases with the increase of the friction coefficient.(3)Two sets of seismic waves with the same average response spectrum but different durations were obtained by using actual seismic waves and synthetic artificial waves,which were used as ground motion input,and the effect of duration on the seismic response of the friction isolation system was analyzed.The calculation results show that when the friction isolation system exhibits approximately linear elastic behavior,the duration of the ground motion has little effect on the seismic response.However,when the friction isolation system exhibits significant friction nonlinear motion,the maximum relative displacement of the structure is larger because the acceleration of the seismic wave increases rapidly and the acceleration of the structure increases slowly in the short-term duration;a larger relative displacement will make the structure suffer larger spring force,and the maximum friction force is fixed,so the maximum acceleration of the structure under short-duration seismic wave excitation is also larger.(4)The near-fault natural waves containing pulses of different periods are used as seismic input,and artificial waves with the same response spectrum but no pulses are synthesized as the control to analyze the impact of pulses on the response of the friction isolation system.The calculation results show that the maximum relative velocity,the maximum relative displacement and the maximum acceleration of the friction isolation system are larger under the action of pulse wave.This is because the ground will maintain a large codirectional acceleration when the pulse occurs,and the increase of the structural acceleration depends on the increase of the relative displacement,so the structure and the ground will have a large relative acceleration.Thus the relative velocity and relative displacement of the structure continue to increase to a larger value,and a larger relative displacement results in a larger spring force and ultimately a larger maximum acceleration of the structure.When the period between the natural period of the structure and the seismic pulse period is relatively large,the pulse duration is short and its impact on the response of the seismic isolation system is small.