Seismic Fragility Analysis Of Steel Framed Structure With Self-Centering Braces Considering Long-Period Ground Motions

For the traditional seismic structure,its structural ductility makes it only partially damaged,so as to achieve the defense goal of it will not be damaged when it encounters slight earthquakes,moderate earthquakes can be repaired,and strong earthquakes will not collapse.However,the results of many seismic surveys in recent years show that the traditional structure will deform after the earthquake,which is large and irreversible,and greatly affects the normal use of buildings.As a result,the recoverability of buildings after an earthquake is becoming an important objective in seismic designSelf-centering Braced Steel Frame(SC-BSF)is a new type of structural system.The special resilience characteristics of flag-shaped of self-centering brace are used to realize self-centering function.In this paper,seismic fragility of SC-BSF structures is investigated based on incremental dynamic analysis(IDA),which takes into account the effects of being subjected to long-period ground motion.The seismic performance of the structure is evaluated comprehensively from the probability levelThe main works are as follows:1.The basic theory of SC-BSF structure model and fragility analysis.The structure and working principle of self-centering cable support based on precompression disc spring are introduced,and the numerical simulation and verification are carried out.The finite element analysis model of SC-BSF structure is established based on OpenSEES.The principle and steps of incremental dynamic analysis method are introduced.The maximum interlayer displacement angle and residual interlayer displacement angle are selected as damage index and peak acceleration(PGA)as strength index.The principle and steps of vulnerability analysis method are introduced,and the performance level and threshold standard suitable for SC-BSF structure are determined.2.fragility analysis of SC-BSF earthquake under common ground motion.According to ASCE7-10,10 common ground motions were selected from the Pacific Earthquake Engineering Research Center,and the peak acceleration of ground motion was adjusted to 10 kinds of amplitude.The maximum interlayer displacement angle and residual interlayer displacement angle are used as structural damage indexes,and PGA is used as strength index for seismic fragility analysis.The results show that the maximum story drift angle of SC-BSF structure meets the limit requirements of 0.4%and 2.0%in Seismic Design Code of Building under frequent and rare earthquakes.The residual interlayer displacement angles of each layer are less than 0.5%,and the structure has excellent repair value.3.Seismic fragility analysis of SC-BSF structure under long-period ground motion.The Fourier function is used to convert the time domain diagram of the ground motion into the frequency domain diagram.According to the frequency domain diagram,the long-period seismic wave is selected,and the peak acceleration is adjusted to 10 kinds of amplitude.The maximum interlayer displacement angle and residual interlayer displacement angle are used as structural damage indexes,and the PGA is used as strength index for seismic fragility analysis.The results of structural fragility analysis under ordinary ground motion and long-period ground motion are compared.The results show that due to the long basic period of SC-BSF structure,it is easy to form resonance with long-period earthquakes,which aggravates the seismic response of the structure.Under rare earthquakes,the collapse probability of SC-BSF structure under long-period ground motion increases by 7.17%compared with that under ordinary ground motion.