Study On The Seismic Performance Of Isolation Structures Under Near-fault Three-dimensional Ground Motio

As a popular structural form in rural areas,both frame structure and masonry structure with a bottom frame structure require special attention to their seismic performance.Earthquake motion is complex and random,and studying the structural response and seismic performance of typical rural buildings under complex earthquake motion characteristics can provide theoretical support for seismic design of typical rural building structures that consider complex earthquake motion characteristics.This has certain reference value in the implementation of disaster prevention and mitigation in the "Rural Revitalization" policy in China.In this paper,six types of complex seismic records with different characteristics were selected,and numerical models of frame structures,masonry structures with a bottom frame structure,and their isolation structures with different numbers of floors were established.The seismic response of rural structures under complex three-dimensional seismic characteristics was studied through seismic time history response analysis.The main work and conclusions are as follows:(1)Six different types of near-fault seismic records with different characteristics(three types of site conditions and whether they contain velocity pulse type)were selected from the Pacific Earthquake Engineering Research Center seismic motion database,and their amplitude and frequency characteristics were studied.The results show that based on the amplitude characteristics of the earthquake motion,pulse-type seismic motion in hard and soft soil sites may cause stronger structural response.Based on the frequency characteristics of the earthquake motion,in the horizontal direction,the average spectrum of the acceleration response of pulse-type seismic motion is significantly larger than that of non-pulse-type seismic motion in the longer period range(about 0.5～4.0s);in the vertical direction,the acceleration response spectrum of vertical seismic motion is generally concentrated in the short period range.(2)Six seismic motions with different characteristics of large earthquake intensity were input into the PERFORM-3D structural model to calculate the seismic response parameters under dynamic elastic-plastic time history.The analysis results show that in the frame structure,pulse-type seismic motion in hard and soft soil sites can cause stronger structural response under large earthquake intensity.Under the action of the six types of seismic motion,the vertical floor acceleration amplification effect appears in all structures,indicating that near-fault seismic motion has a significant vertical effect on the acceleration response of the floor.The isolation frame structure with two floors is very sensitive to velocity pulses,and the relative seismic performance of the first floor isolation rate is low.The isolation structure with four and six floors has a higher cost-effectiveness ratio.(3)In the masonry structure with a bottom frame structure,pulse-type seismic motion can cause more severe seismic response to the structure;in the isolation structure of the masonry structure with a bottom frame structure,pulse-type seismic motion in soft soil can cause greater seismic response to the structure.The bottom frame structure is mainly sheared and damaged by brick masonry,and compared with the bedrock site,the isolation rate of the bottom frame structure with isolation in hard and soft soil sites is reduced.From the perspective of the impact of velocity pulses,the velocity pulse effect will reduce the isolation rate of the bottom frame structure with isolation on each floor.Based on the analysis results,considering the seismic performance and economic rationality,low-rise masonry structures with a bottom frame structure do not require basic isolation design.