Research On Elasto-plastic Seismic Response Computational Model For Steel Bridges

Owing to excellent mechanical properties and gradually promoting economic competitiveness,the application of steel bridges in China is rising increasingly.Despite the good seismic performance,steel bridges still sustain plastic damage under strong earthquakes,such as local deformation of steel plates.However,the existing elasto-plastic seismic response computational models for steel bridges cannot meet the requirements of both calculation accuracy and engineering applicability.Therefore,the purpose of this thesis is to establish a practical method for calculating elastic-plastic seismic response of steel bridges,which can ensure the accuracy of calculation and meet the needs of engineering design.Taking steel piers,the seismic vulnerable member of steel bridges,as the research objects,a simplified hysteretic model for steel piers considering the local deformation of steel plates was proposed on the basis of structural seismic performance analysis;Furthermore,in order to simulate the steel structures or components with different deformation characteristics in horizontal directions,a modified multi-shear-spring model considering multi-directionality was proposed based on the modification of the traditional multi-shear-spring mechanical model.The main contents and conclusions are as follows:(1)Through the finite element computational models of steel piers,the influence of welding residual stress and initial geometric imperfection on the structural hysteretic behavior was discussed.The results show that the influence of welding residual stress is negligible and initial geometric imperfection has little effect on the structural hysteretic behavior.Therefore,initial imperfections of steel piers could be ignored when the finite element method is applied to analyze structural seismic performances.(2)The seismic performance bearing capacity and ductility limit states for steel piers made of Q345qC steel were studied,and the relationships between limit states and structural parameters,such as the ratio of diameter to thickness(the ratio of width to thickness)and the slenderness ratio,were obtained by regression analysis.Furthermore,the empirical formulas for limit states of Q345qC steel piers obtained from this thesis and the ones of Japanese steel piers suggested by Japanese scholars were compared.The results show that for circular piers,the relationships between seismic performance limit states and structural parameters are almost not affected by steel material properties;but for box piers with transverse and longitudinal stiffeners,the structural seismic performances are strongly dependent on the material type when the structural parameters are identical.However,the variation trends of structural seismic performances with structural parameters are similar even for box sectioned steel piers made of different steel materials.(3)On the basis of the research on the structural seismic damage characteristics,a simplified hysteretic model for steel piers considering the local deformation of steel plates was proposed.The basic characteristics on hysteresis curves,hysteresis curve equation and degradation rule of the proposed hysteretic model were discussed.Then,the effectiveness of the hysteretic model under cyclic loading conditions was validated,and its applicability in the calculation of structural elasto-plastic dynamic seismic response was also investigated through dynamic response analysis.(4)In order to simulate steel structures or components with different mechanical properties in horizontal directions,a modified multi-shear-spring model considering multi-directionality was proposed on the modification of the traditional multi-shear-spring mechanical model.With steel dampers as the target objects,hysteresis curve equation,determining methods of the stiffness ratio and the shape parameter in the modified model were illustrated.(5)The modified multi-shear-spring model was used as the simplified analytical model for U-shaped steel dampers.The effectiveness of the modified model was validated by pseudo-static hysteretic behavior analysis of the steel damping element.And the elasto-plastic seismic response of a curved bridge featuring a steel hysteresis device was investigated to verify the applicability of the model in the structural seismic response analysis.