Research On Seismic Vulnerability Of Steel Frame Structures Considering Age

Steel structure is widely used in the process of urban modernization due to its advantages of high strength,high toughness and convenient construction.However,the weakening of the seismic performance of structural members due to the corrosion of steel,which in turn leads to the reduction of the overall structure’s seismic capability,which seriously restricts the vigorous promotion of steel structures.Especially when the rusted steel frame structure is damaged to different degrees after the earthquake,it will bring serious social and economic losses.Therefore,studying the seismic performance of steel structures after corrosion is an urgent problem to be solved in the seismic performance evaluation of existing steel structures.Based on this background,this article uses the experimental research and theoretical analysis as a means to carry out the following research work:(1)Low cycle reciprocating loading test and finite element analysis of corroded steel frame beams and corroded steel frame columns.The effects of different degrees of corrosion on the hysteretic curve,skeleton curve,bearing capacity,ductility and energy consumption of steel frame beams and columns were compared and studied.The results show that as the degree of corrosion increases,the bearing capacity,ductility,and energy consumption of steel frame beams and steel frame columns gradually decrease.The finite element analysis method used in this paper can also effectively simulate the hysteretic behavior of corroded steel frame beams and steel frame columns.On this basis,the parameter analysis of the finite element model of steel frame beams and steel frame columns is conducted,and the degradation laws of seismic performance of corroded steel frame beams and columns are studied in depth.The functional relationship between the characteristic parameters(Yield bending moment,peak bending moment,ultimate bending moment,and corresponding corner value and ductility coefficient)of the skeleton curve of the corroded steel frame beam as a function of the weight loss rate and the functional relationship of the characteristic parameters of the skeleton curve of the corroded steel frame column as a function of the degree of corrosion and the axial compression ratio are given respectively.(2)Based on the modified Ibarra-Krawinkler(IK)model,Through theoretical analysis and combining test data and finite element data regression results,propose a tri-fold skeleton curve model that can consider the influence of corrosion,and the formula for calculating the characteristic points of the skeleton curve is given.And the restoring force models of rusted steel frame beams and steel frame columns are established.At the same time,compare the calculated hysteresis curve with the experimental hysteresis curve,the good agreement between the two shows that the established restoring force model of corroded steel frame beams and columns can accurately reflect the hysteretic characteristics of corroded steel frame beams and columns.(3)Based on the restoring force model of corroded steel frame beams and columns,Open Sees finite element software was used to build a four-year-old plane steel frame structure of the overall structure concentrated plastic hinge model.PGA was selected as the index of ground motion intensity,and the maximum inter-layer displacement angle θmax of the structure was used as the seismic response index of the structure,then,the seismic vulnerability analysis based on the IDA analysis method is performed on each structural model,and obtain the vulnerability curve of the model structure.The results show that as the degree of corrosion increases,the probability of different limit states occurring when the steel frame structure is affected by the same earthquake intensity increases,corrosion reduces the seismic performance of steel frame structures.