Dynamic Analysis Of Base-isolated Structure Under The Action Of Near Fault Impulse Ground Motion And Its Component

In the near-fault region where an earthquake occurs,two different types of velocity pulse-type ground motions can be generated due to the fault sliding direction and the mechanism of ground motion propagation,which are respectively near-fault sliding impulse ground motion and near-fault frontward movement.Pulse ground motion.These two ground motions exhibit different long-period characteristics due to their different speed pulse patterns.In this paper,based on the energy-based velocity pulse identification method,20 typical near-fault pulse-type ground motions are identified from the Taiwan Chichi earthquake record,and 10 types of far-field harmonic ground motions are selected.Two types of pulsed earthquakes are compared and analyzed.Differences between dynamic and far-field harmonic ground motion characteristics.The base-isolated structure has a good shock-absorbing effect under the action of common ground motion,but due to the rich long-period components of the near-fault pulse-type ground motion,it may have a great impact on the seismic performance of the base-isolated structure.Therefore,the purpose of this paper is to study the influence characteristics of two types of near-fault velocity pulses on the base-isolated structure,and to provide reference value for the seismic fortification of the base-isolated structures in the near-fault region.The main conclusions obtained are as follows:(1)There are significant differences in the ground motion characteristics of the two types of near-fault pulse-type ground motions.The acceleration response spectrums of the two types are similar,but the velocity response spectrum and the displacementresponse spectrum are very different,reflecting the long-period characteristics of two types of ground motions.The difference.Near-fault forward directional pulse ground motion The first-harmonic vibration has a small difference in Fourier spectrum amplitude from the second and third predominant frequencies,and has a richer long-period component than the slam-pulse-type ground motion.,(2)Sliding impulse velocity pulses make the displacement response and base shear force of the 5-story and 10-story seismic isolation structures expand by about 1.2 times and 1.4 times with respect to non-pulse ground motions,and the forward direction velocity pulses make 5 layers.The displacement response of the 10-story isolation structure is increased by about 1.1 times and about 1.2 times with respect to non-pulsed ground motion.The influence of the forward directional velocity pulse-isolated structure on the shear force of the basement is not great.Therefore,when there are fewer seismic waves with speed pulses that are available for the proposed site,it is recommended that the pulse impact coefficient be between 1.10-1.40.(3)In the frequency range of 0.78-1.56 Hz,the impact of two types of pulsed ground motions on the structural response is not significant.In the 0.39~0.78 Hz and0.20~0.39 Hz frequency bands,the response of the structure is relatively large.At the same time,the influence of the two types of pulsed ground motions on the structural response is also significantly different.The sliding pulsed ground motion is more prone than the forward directional pulsed ground motion.The ability to stimulate the reaction of the structure can explain that the difference in the characteristics of the long-period components of the two types of ground motions is mainly concentrated in these two frequency bands.In the 0~0.20 Hz frequency band,the forward directional pulse ground motion is slightly larger than the sliding impulse ground motion in response to the structure.