Research On Seismic Performance Of Layered Assembled Light Steel Frames Based On Damage Performance

The beam-column connection joint is a key transmission part in an assembled structure,and a large amount of brittle damage can occur during earthquakes when conventional steel frame beam-column joints are welded.To prevent brittle damage at the joints,the plastic hinges are kept away from the joint area by structural treatment,so as to meet the seismic design criterion of "strong joints and weak members”.Based on the demand of prefabricated building industry and the construction site process practice,considering the mechanical characteristics of joints,a novel type of fully-bolted joint with layered assembly was proposed.The force transfer mechanism,failure mode and seismic performance of joint were revealed through quasi-static test.Based on the damage performance,finite element models of novel joints were established,and IDA analysis was carried out to obtain the vulnerability curves under different damage indexes.The main work carried out is as follows:(1)Four joint specimens,including novel layered assembled fully-bolted joints and conventional joints,were designed.The mechanical and seismic performance of the specimens were studied by the quasi-static test.The failure mechanism,failure characteristics,and mechanical properties of the two types of joint constructions were examined.Their seismic behaviors,such as hysteretic performance,energy dissipation,ductility,stiffness,and strength degradation,were investigated to determine the effect law of various structural forms on joints seismic performance.(2)The effects of structural parameters,including column end plate thickness,square steel tube wall thickness,flange thickness of joint domain,inner sleeve wall thickness,axial compression ratio and inner sleeve projection height,were systematically analyzed to improve the seismic performance of joints.(3)The steel frame models with novel layered assembled fully-bolted joints and conventional joints were established,respectively.A damage model for steel frame structures under ground motion was proposed.The peak acceleration(PGA)was used as the ground motion intensity index,and appropriate ground motion records were input to conduct incremental dynamic analysis(IDA).The probabilistic relationship between the seismic response of steel frame structures and ground motion intensity index was established.(4)The performance level and damage level of the steel frame were determined and the seismic fragility analysis of steel frame model was carried out.The seismic fragility curves of two kinds of steel frame models were drawn with single parameter damage index and double parameter damage index,respectively.The effects of different joint structures and damage indexes on the seismic fragility of structures were studied to provide reference for seismic safety assessment of structures.