Study On Seismic Fragility Of The Steel Frame With New Fully-bolted Assembled Joints

The prefabricated assembled steel structure has the advantages of good seismic performance,convenient construction and recyclable components,and low consumption of building materials,which conform with the concept of green construction.The steel frame beam-column joints with fully-bolted assembly can not only meet the design standard of“strong joint and weak member”,but also have a certain impact on the seismic performance and assembly quality of the whole structure.To explore the applicability and feasibility of the new fully-bolted assembled joints applied to the whole frame,based on the seismic performance analysis of the new fully-bolted assembled frame beam-column joints carried out by the same research group,a simplified mechanical analysis model of the joints was proposed,and a three-dimensional space frame model of the new fully-bolted assembled joint steel frame was established by SAP2000 software.The seismic performance of the whole structure was discussed through Pushover analysis and dynamic time history analysis.Based on the damage performance,the damage parameter model of the structure was established,the fragility curve was drawn to evaluate the collapse resistance of the structure.The main research works are as follows:(1)The calculation formulas of yield flexural capacity and ultimate flexural capacity of the new fully-bolted assembled beam-column joints were modified and verified.The connection properties of the two types of joint(the traditional column-through joint and new fully-bolted core tube joint)were determined.The simplified mechanical analysis model of the joints was proposed,and its rationality and reliability were evaluated by comparing with the experimental results.The results show that the error rate of the modified formula and the simplified mechanical model is less than 12%,with reliable accuracy.(2)The three-dimensional space models of multi-story steel frame with new joints and traditional joints were established,and the dynamic time history analysis was implemented.Under the action of 8 degree frequent and rare earthquakes,the seismic performance indexes,including interlayer displacement angle,lateral displacement and base shear,of the two types of structures were discussed and compared.Additionally,to explore the influence of different parameter settings on the dynamic response of the whole structure,the ultimate bearing capacity and initial rotational stiffness of the new joints were changed.The results show that the multi-story steel frame with new joints has good seismic performance,and increasing the ultimate bearing capacity and the initial rotational stiffness of the joints will reduce the top layer displacement and the maximum displacement angle of the steel frame.(3)The static elastic-plastic analysis was carried out on the space analysis model of highrise new fully-bolted assembled joint steel frame with four different layers,and the distribution of plastic hinges,displacement and deformation responses of the structure were systematically analyzed.Additionally,based on the classification standard of structural performance level and the results of static elastic-plastic analysis,the limit values for the performance level of assembled steel frame structure were determined.The results show that the high-rise steel frame with new joints conforms to the idea of “capability design”,and the performance level limit of the prefabricated steel frame structure in the usable range is [0.1,0.85].(4)Incremental dynamic time-history analysis was carried out to develop the fragility curves of the structure,which were based on the single-parameter damage model and the twoparameter damage model.And,the probability of exceedance corresponding to each performance level of the structure under different damage models was discussed.According to the structural performance evaluation criteria,the collapse resistance of the structure was evaluated on the basis of the modified structural collapse redundancy.The results show that the collapse probability of the high-rise steel frame with new joints is less than 5% under 8degree rare earthquake,and it has sufficient collapse redundancy.