| With the growth of steel output in China,the number of steel bridges in traffic engineering will increase significantly,but the theoretical research on the seismic design of steel bridges is relatively lagging.It is urgent to optimize the checking method for structural seismic performance that meets China's national conditions.To this end,the structural seismic performances under horizontal bidirectional earthquakes were studied through numerical simulation and quasi-static test in this study,and two types of calculation models were proposed to calculate seismic response of steel bridges that can consider the local instability effect of steel plates,which are hybrid-element model and simplified analysis model.The main work and research results of this study are as follows:1.Taking single-column rectangular-section and circular-section steel piers as the objects,the shell-element model and modified two-surface hysteretic constitutive model were used to analyze structural failure processes under horizontal unidirectional or bidirectional cyclic loading.The bearing capacity,ductility and local deformation characteristics of the structures under different loading paths were discussed.The results show that the steel piers are more prone to local instability failure under the horizontal bidirectional cyclic load.2.According to the out-of-plane deformation characteristics of steel plates,lengths of structural seismic damaged zone Ld was defined,and the empirical formulae of the lengths of seismic damaged zone Ld for rectangular-section and circular-section steel piers under horizontal bidirectional cyclic loads were established by parameter analysis.The results show that the proposed empirical formulae can conservatively reflect the length of the region where local deformation may occur,and the hybrid-element calculation model established by these formulae can reduce the amount of calculation while ensuring calculation accuracy.3.Taking a half-through steel arch bridge as the object,fiber-element calculation models and hybrid-element calculation models were established to analyze the structural seismic response under strong in-plane earthquakes.Local instability and ultra-low cycle fatigue damage characteristics of structures with different steel-plate thicknesses of main arch ribs were analyzed,and reasonable seismic response calculation models for this type of structure under different conditions were discussed.On this basis,the development of steel-plate local deformation and ultra-low cycle fatigue damage at the welded joint under in-plane and three-direction ground motion input were compared;the results show that increasing the transverse seismic input based on the in-plane seismic input will accelerate the seismic damage development of steel arch bridges.4.Taking the single-column square-section steel piers as the objects,length the structural seismic effective damaged zone Led was defined according to the calculation results obtained by the hybrid-element model,and the equivalent hysteresis model of fiber elements in this area was established based on the modified two-surface hysteretic model of steel.Finally,an improved fiber model calculation method for steel piers that can consider the local instability effect of the steel plate was proposed,and the comparative analysis verified that the improved fiber model has a high calculation accuracy and efficiency.5.Two square-section thin-wall stiffened steel piers were manufactured,and the horizontal bidirectional seismic load was simulated by applying cyclic horizontal loads along the diagonal direction of cross section to study the structural seismic performance and failure mechanism.The effectiveness of improved fiber model calculation method proposed in this paper was further verified through the comparision of hysteretic curves.6.Taking circular-section steel piers as the objects,a multi-shear springs model that can be applied for horizontal bidirectional seismic response analysis and can consider the local instability effect of steel plates was established.The effectiveness of the proposed model was verified by comparison with the calculation results and efficiency of the shell model. |
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