Multi-scale Modeling And Analysis Of Bridge Considering Soil-structure Interaction

Bridge is an interdependent architecture that its superstructure is connected between the basis and foundation and the architecture is constituted by structure-foundation-soil.Practice on earthquake engineering indicates that the seismic wave will act on the structural system through the propagation of soil when under seism action.Therefore,the bridge system seismic response analysis that considers the SSI effect is worth.However,the analysis of the bridge system consumes so much time and memory that the computational efficiency is small or even impossible to achieve due to the relatively large soil-structure interaction in the bridge structure.To resolve the issue we adopt a multi-scale modeling method to conduct the seismic analysis of the structure and the main work and conclusions are as follows:(1)Based on the theory of multi-scale modeling structure,we use refined unit to simulate the key(or easy damage)positions in the same structural model and use macroscopic element to simulate other positions.By Searching for the cross-connection method between different units,the deformation coordination between different units is achieved.(2)As a result of different units in the cross-section connection will relax a part of the freedom degree,the multi-scale model is smaller than the actual model,so the stiffness of the multi-scale model was modified.To verify the consistency between the modified multi-scale model and engineering practice,we contrast the seismic displacement,velocity and acceleration response between the revised multi-scale model and unit model.(3)Reasonable ground motion input is a key factor in ensuring structural seismic response for the overall bridge system that considers soil-structure interaction,and the ground motion input should be a seismic wave at a certain depth in the ground rather than ground motions based on surface records.So this article uses Thomson-Haskell transfer matrix method and deduces the transfer function of ground motion through layered soil.Then by using the transfer function and the surface recorded by the seismic waves(EI Centro wave and Tianjin wave),we got the corresponding underground seismic waves and has verified its correctness to make preparations for the seismic response analysis of follow-up structures.(4)By comparing the displacement response,the pier shear,the hysteresis curve and the energy dissipation capacity of the underground ground motions,we explored the parameters such as soil,longitudinal reinforcement and stirrup and analyzed the influence of earthquake response on the bridge system.The results showed that: when considers the soil-structure interaction,the soil has a certain dissipation effect on the seismic energy,and the demand for seismic performance of the bridge is reduced,so the soil-structure interaction in the seismic design of the bridge should be considered;when increase the longitudinal reinforcement ratio,the maximum displacement of the pier top is decreasing,and the maximum shear force at the bottom of the pier is increasing,however,when the reinforcement rate continues to increase,the pier at the end of the concrete will be damaged before the steel,the phenomenon of super-gluten damage appears,and the bottom of the maximum shear decreased instead,so the vertical reinforcement rate should not be too large;when increase the stirrup rate,the maximum displacement of the top of the pile change is small and the maximum shear force at the bottom of the pier fluctuates within a certain range,in general,the hoop rate has little effect on the energy dissipation capacity of the bridge structure.