Study On The Influence Of U-Shaped Abutment-Backfill Interaction On Seismic Performance Of Girder Bridges

Located between the Pacific Rim seismic zone and the Asia-Europe seismic zone,China is one of the most active seismic zones in the global continental region.As an important part of the road,the bridge plays the role of a lifeline in the process of earthquake relief.Statistics show that the medium and small span continuous beam bridges are numerous and widely distributed in China,and occupy a large proportion in the bridge system.Gravity U-shaped abutment is an important component of medium and small span beam bridges and is widely used in China.The traditional design uses the abutment as an independent retaining structure,completely ignoring the abutment-back earth interaction.However,many earthquake damage investigations in the past have shown that the abutment-back soil interaction will cause damage to the back wall of the abutment,the collapse of the back of the platform and the failure of the abutment foundation,which will further lead to serious damage such as the falling beam.In order to reveal the influence of U-shaped abutment-back soil interaction on the seismic performance of medium and small span beam bridges,the main research work and conclusions of this paper include:(1)Based on the severely damaged real bridge in the Wenchuan earthquake,a series of typical continuous girder bridges were constructed according to the number of spans and piers.At the same time,according to the structure and force characteristics of the gravity U-shaped abutment,four types were proposed.Simplified analysis model,based on the OpenSEES open source platform,established a three-dimensional refined nonlinear analysis model to explore the influence of different analysis models on the dynamic characteristics of the natural vibration period,vibration mode and vibration mode of typical bridges.The research shows that with the fine model as the benchmark,the roller model can only accurately simulate the first-order period and mode shape of the bridge example,and the high-order error is very large.The bearing model and the spring model can accurately simulate the bridge example.The order period and mode shape;the number of spans and the form of piers have a certain influence on the natural vibration period of the bridge and the participation quality of the vibration mode,but have almost no influence on the vibration mode.(2)For the typical bridge example,the nonlinear time-history analysis method isused to study the four abutment-back soil interaction simplified analysis models and their parameters from the seismic displacement of the superstructure and the seismic internal force of the substructure.The influence law of the value on the seismic response of the bridge case,and the influence characteristics and laws of the abutment-back earth interaction under different structural design parameters such as span and pier form are discussed.The research shows that with the fine model as the benchmark,only the error of the bearing model is very small;the variation of the initial stiffness of the simplified analysis model has a great influence on the displacement of the upper structure of the bridge,especially when the PGA is large;the variation of the yield strength of the model is simplified.The seismic response has no effect;the seismic response of the bridge is the largest when the abutment is increased by 5 times.The seismic response of the bridge is greatly reduced without considering the quality of participation.The span and the form of the pier have less influence on the displacement of the main beam,but increase the span.The number and the single-column double-column pier can increase the displacement of the bearing and reduce the internal force of the pier.(3)According to the parameter analysis results of the above bridge example,select the representative bridges which are relatively unfavorable in the parameter analysis,and use the IDA analysis method to calculate the main beam displacement IDA curve,the pier column curvature ductility IDA curve and the support.Displacement IDA curve,according to the criterion of different failure states,respectively evaluate the failure state of bridges with four different abutment models under different ground motion strengths,and further construct the seismic vulnerability curves of each state,thus The bridge structure system is evaluated for seismic performance.The research shows that the piers and supports adopting the roller model and the spring model enter the failure stage earlier and finally reach the complete failure state;the members of the bridge adopting the bearing model are almost in the elastic stage;the roller model and the spring model are adopted.The seismic performance of the bridge structure system is poor.(4)Combining the above conclusions,considering the analysis accuracy and calculation cost,the spring model is more recommended in seismic design;initial stiffness and abutment participation quality are key parameters affecting the abutment-back soil interaction,but the yield strength is not The key parameter is that the yield strength of the abutment-back soil interaction is generally large and theyielding phenomenon is not easy to occur;the span and the pier form will have some influence on the dynamic characteristics and seismic response of the bridge,but for the four U-shaped abutments-The analysis results of the back-soil interaction and its laws have little effect.