Seismic Fragility Analysis Of Steel Frame Structures Considerin Gage Under Urban Atmospheric Environment

Steel structure is considered to be an important development direction for futurebuildings with its advantage of high strength,light weight and industrializedconstruction.Study on design method?design theory?structural safety and suitability forsteel structure in practical application was more emphasized,but study on steeldurability was relatively lagging.And with the acceleration of urban industrializationprocess,Environmental pollution was worsening,for example,industrialatmosphere,sulfur dioxide and so on.The service environment was increasingly severeand affected the promotion and application of steel structures to some extent.The correlative research for steel frame structure considering multiage under urbanatmospheric environment was carried out from material properties,components andstructure aspects combined with experimental research,numerical analysis andtheoretical analysis methods.(1)The monotonic tensile test of standard sample was carried out after acid saltspray accelerated corrosion test in the paper.By analyzing test data,The linear regressionanalysis was adopted to illustrate the relationship between steel mechanical propertiesand mass loss rate,and then significant test was used to proved the applicability andeffectiveness of the fitting equation with mathematical method.Finally,the deteriorationlaw of steel mechanical properties was established based on material level.(2)To study variation of specimens bearing capacity,strength,stiffness,energydissipation capacity and other property indexes in different corrosion level and establishdeterioration law based on component level.By changing the loading mode andcorrosion rate,Three group connection specimens in different corrosion level were tested under cycle loading and the deterioration law of specimens was obtained with thechange of corrosion rate,loading cycles and loading mode.Test results showed thatcompared with the no corrosion specimens,Specimens ultimate bearing capacity andenergy dissipation capacity decreased;Strength and stiffness deterioration also decreasedobviously with the increasing of corrosion time.(3)Based on experimental investigation,Finite element analysis on specimens indifferent corrosion level was executed by ANSYS.The comparison between theexperimental results and FEM results indicated that finite element analysis results andexperimental results were basically similar;Specimens failure mode were consistentwith test results.The analysis results verified the feasibility of using ANSYS to analysismechanical property of corroded specimens.(4)According to steel corrosion rate under acid atmospheric environment and thedeterioration of steel mechanical properties,a15-floor residential steel structures weredesigned based on current design code and its service time was assumed to be0,15,30,45years.By numerical simulation and IDA-based method,Seismic fragilitycurves of steel frame structures under acid atmospheric environment were createdconsidering service time.The results indicated that with the increasing of structure agethe maximum drift angle would exceed the limit value in codes and structure damagestate would developed by slight damage to moderate damage,leading a higherprobability of collapse;In the same seismic intensity,The failure probability of the steelframe structure beyond the limit state would be increasing,but the failure probabilityrepresented by the overall structure damage was smaller than the failure probabilityrepresented by maximum drift angle.The increasing extent of failure probability wouldbecome smaller,as rust layer cut off the contact between steel and outside media.Theresearch results could provide theoretical basis for the assessment of structure seismichazard and loss after earthquake under service time.