Research On Seismic Performance And Seismic Fragility Analysis Of Multi-aged Steel Frame Structure Under Coastal Atmospheric Environment

Recently the steel structure has been widely used due to its advantages,such as lightweight,high strength,good plasticity,and good seismic performance.Since the steel has its own disadvantage of poor corrosion resistance,we can not imagine how terrible it would be if the structure located in serious corrosion environment as well as seismic-prone areas.Thus it is an urgent problem to assess the seismic performance of corroded steel structure.Under the auspices of the National Science and Technology Support Project in the 12 th Five-Year Plan named “study and illustration of the key technology of simulation and assessment for the multi-aged buildings in the city”,this paper has systematically studied the seismic performance of corroded steel frame structures and seismic vulnerability of multi-aged steel frame structures in the coastal atmospheric environment.The main research contents and conclusions of this paper are as follows:(1)With the test technique of outdoor accelerated corrosion,21 groups standard steel material specimens and 7 planar steel frame structures were accelerated corroded under coastal atmospheric environment.Then,the tensile test and quasi-static test were carried out respectively.Based on tensile test data,the linear regression relationship between the steel mechanical properties(yield strength,ultimate strength,elongation,elastic modulus)and weightlessness rate is established.According to the quasi-static test data,the influence of different corrosion degrees,axial compression ratio and loading path on seismic performance of planar steel frame structure(containing hysteris curve,skeleton curve,strength and stiffness degradation,energy dissipation of steel frame,ect.)are analysed.The results show that corrosion has a significant impact on the seismic performance of planar steel frame,and with increase of corrosion degree,the ultimate bearing capacity decreases obviously.The more serious degradation of strength and stiffness,the more obviously energy dissipation capacity decreases.So as the brittle damage.In a certain range,with the increase of axial compression ratio,the ultimate bearing capacity of steel frame structures decrease slightly,the strength and stiffness degrade seriously at the later stage of loading,and the energy dissipation capacity of the specimens degrade.The loading path has a great influence on the plastic deformation and energy dissipation capacity of planar steel frame structures.(2)Based on the tensile test results of steel,the constitutive model of corroded steel is established.Then,the nonlinear analysis of planar steel frames were carried out by using the finite element software ABAQUS6.12-1 to consider the influence of the corrosion degrees,axial compression ratio and loading path.Comparing the analysis results with the test results,it is found that they have good consistency in aspect of failure state,hysteretic curve and skeleton curve.That verifies the adaptiveness of the steel constitutive model,which provides the theoretical support for the subsequent vulnerability analysis.(3)Based on the degradation rules of mechanical properties of corroded steels obtained from tensile tests,the corrosion rate of steel in typical coastal atmospheric environment and the rust time of in-service steel structure determined by field research,the finite element models of 6-story steel frame structures of different service times(30years,40 years,50 years,60 years)and the finite element models of 3-story and 9-story steel frame structures were established in ABAQUS.The IDA is carried out by using the PGA as the ground motion intensity measure and maximum interstory drift angle as the seismic demand measure.At the same time,the Pushover analysis of each model is carried out with SAP2000,and the value of each limit state is determined by Pushover curve.On the basis of the analysis results of IDA and Pushover,the seismic vulnerability of each model is analyzed,and the seismic vulnerability curves considering the influence of service time and layer number are established.The results show that with the increase of the service time,the probability of structural extensive damage and collapse under the same ground motion intensity increases,indicating that the corrosion causes the decline in seismic performance of the structure.Also,the effect of layer on the probability of exceedance is gradually evident with the increase of the state of failure.The research results can provide the theoretical basis for the seismic risk assessment of urban multi-age buildings.