Study On Seismic Damage Performance & Fragility Of In-service Steel Frame Structure Under Offshore Atmospheric Environment

The research in durability and seismic behavior of in-service steel frames were carried out in offshore atmospheric environment by means of combining experimental study and finite element numerical analysis methods, including pseudo-static destruction tests of corroded plane steel frames ? seismic damage model study and seismic fragility analysis. The specific research were carried out from the following aspects:(1) The low cycle loading tests and tensile experiments were carried out respectively for four scaled-down plane steel frames and 63 steel material specimen in different degree of corrosion by simulating offshore atmospheric environment. The deterioration rules of steel's mechanical property based on material level and the deterioration laws of carrying capacity ? strength ? stiffness and energy dissipation capacity of the overall structure and each floor have been got,which filled the gaps of the durability study that based on structure level at home and abroad.(2) Using the finite element software ABAQUS to simulate the plane steel frames that in different degree of corrosion. The analysis results were comparied with the test results to find that the two have the same failure pattern, bearing capacity and energy dissipation capacity, as well as the failure pattern which was quite the same. It confirmed that the finite element analysis of the corroded steel frames that considering material degradation can accurately reflect the actual degradation process of steel frames' bearing capacity.(3) On the basis of existing research achievements of seismic damage models and based on the damage model of maximum deformation(inter-story drift), put forward a two-parameter seismic damage model at the whole structure level that considering both the biggest deformation and accumulated energy dissipation effect by introducing energy dissipation parameter.(4) The plane steel frames with different corrosion levels were simulated by finite element analysis software. The deterioration laws of whole initial stiffness K0 of the structure with the increasing of corrosion time was got by using the nonlinear pushover analysis. The time-varying damage model which apply to corroded steel frame was got by introducing the deterioration law into the two-parameter seismic damage model that was proposed above in this paper. Take PGA as intensity measure index and take the damage model that based on deformation and energy, as well as two-parameter time-varying damage model as the performance indicators, the vulnerability analysis was carried out for the structures with different ages. Then the vulnerability curves based on different ages and damage models were compared.