Research On Seismic Response Evaluation Method Of Steel Bridges And Seismic Damage Index Of Steel Material

Researchers haven’t paid sufficient attentions to the seismic design of steel bridges for a very long time since steel bridges usually possess better seismic performances and lower application rates than RC bridges. As the number of steel bridges employed in traffic network has increased rapidly, seismic damage of steel bridges was frequently observed all around the world recently. Considering that the development of seismic design methodology has already fallen behind the construction of steel bridges, it is very urgent and significant to establish a reasonable ductile seismic design method for steel bridges at present.As the structural seismic response analysis and capacity evaluation is the foundation of establishing a reasonable seismic design method for bridges, this paper aimed at proposing a rational seismic response calculation and damage evaluation method for steel bridges. Therefore, the optimal numerical model for seismic performance evaluation of steel structures was investigated and the seismic damage accumulation rule and the assessment method for steel bridges were studied through theoretical analysis and experiments. The main work and achievements in this paper can be drawn as follows:1. Both a fiber model and a shell model were utilized to conduct elasto-plastic seismic response analysis of a long-span steel arch bridge, the effects of fluctuant axial forces in the main members and local deformations on steel plates were discussed and the influence of numerical models on the seismic response assessment of was analysed. The results show that, the fiber model is applicable to seismic performance analysis when the bridge is under a slight damage state, and it is feasible to check the seismic damage for a fiber model based on the strain which averaged on the failure zone.2. Based on the analysis of elasto-plastic behavior of steel columns with a thin-walled rectangular section under cyclic loads and strong earthquakes, the effects of design parameters on the damage zone length was discussed, and then an empirical formula of the seismic damage zone length at the steel connections was proposed. Thus, the principles of element discretization at the seismic damage area on a steel structure were achieved for a multi-scale hybrid model.3. The multi-scale hybrid models of two steel arch bridges were created based on the proposed principles and the elasto-plastic seismic response analysis was carried out, the influence of numerical models on seismic performance estimation was studied, the validity of the proposed principles was verified.4. The multi-scale hybrid model was adopted to perform nolinear time-history analysis of a steel bridge under strong earthquakes and the residual deformation on the structure caused by the main-shocks was discussed. Then the impact of the residual deformation on the deterioration of seismic performance of the structure was investigated. The results show residual deformation caused by the main-shocks affects less on the seismic performance of the structure during the aftershocks.5. Through the experiments of low-carbon steel, which is conventionally used in bridge constructions, under the combined cyclic and monotonic loads, the coupling relation between the ultimate deformation and low-cycle fatigue life of steel material was researched, and the influence of stress triaxiality on the damage accumulation was studied. The results show that there’s no obvious coupling relation between the two kinds of damage, and stress triaxiality affects the damage accumulation of low-carbon steel significantly.6. Real history-recorded earthquake sequences were taken as input ground motions when performing seismic response analysis of a half-through arch bridge using multi-scale hybrid model, the evolution of seismic damage of the bridge under strong earthquake sequences was analysed using different damage indexes. The results show that steel bridge does not fracture though damage accumulated rapidly under strong earthquake sequence, the difference of the evaluation conducted by different damage indexes is very small.