Study On Seismic Behavior And Seismic Fragility Evaluation Of Prefabricated Assembled Bridge Piers Of Socket Connection With UHPC Materials

The prefabricated assembled pier system has attracted great attention from scholars at home and abroad due to its advantages of rapid construction,reliable quality,safety and environmental protection,and has become a new choice for bridge construction programs.As a kind of prefabricated assembly connection method,socket connection has been applied in highway bridges and municipal bridges,but the existing experimental research results show that under the action of earthquakes,the damage of the precast assembled pier with socket connection is serious,which will lead to the interruption of bridge function after the earthquake.In order to improve the seismic performance of prefabricated assembled pier with socket connection,this paper introduces ultra-high performance concrete(a new high-performance material)for plastic hinge area of prefabricated assembled pier with socket connection,and the complex production process of UHPC is completed by the method of factory prefabricationBased on OpenSees,this paper establishes a fiber element finite element model of UHPC prefabricated bridge pier with wet socket connection.Through the quasi static analysis and seismic response time history analysis of the prefabricated pier,the seismic performance of the prefabricated pier is studied and compared with the cast-in-place pier.The main research contents and conclusions of this article are as follows:(1)The structural characteristics and stress analysis methods of various prefabricated assembled pier systems are summarized.The research status of prefabricated assembled pier with socket connection at home and abroad is systematically summarized from the three aspects of experimental research,theoretical research and the use of new materials.The rationality of the application of high-performance new material UHPC in prefabricated bridge piers with wet socket connection was analyzed,and the research contents and research methods of this article were clarified.(2)The modeling method for analyzing the seismic performance of prefabricated bridge piers with wet socket connection based on OpenSees software is given.In this paper,the rebar model for the lower part of the bridge pier required for modeling is proposed.Research and give the selection of rebar,concrete and fiber elements in the model,the reasonable division of fiber cross-section,the selection of boundary conditions and loading methods,etc..The rationality and reliability of the modeling method are verified by comparing with the existing experimental results,which provides a reference for the finite element modeling analysis of the same type of prefabricated pier.(3)The seismic performance of prefabricated assembled bridge piers of wet socket connection with UHPC materials was calculated and studied.In this paper,UHPC is applied to the plastic hinge area of the lower part of prefabricated assembled bridge piers of wet socket connection with UHPC materials.The quasi-static analysis results of the same parameters of the prefabricated assembled bridge pier of wet socket connection with UHPC materials is compared with those of the cast-in-place pier.The influence of the design parameters such as constant load axial compression ratio,longitudinal reinforcement ratio,aspect ration,and UHPC section height of the pier on the seismic performance of prefabricated assembled bridge piers of wet socket connection with UHPC materials is calculated.The research results show that the addition of UHPC effectively improves the horizontal bearing capacity and energy dissipation capacity of prefabricated piers,and at the same time makes the rigidity of prefabricated piers improved.Although the ductility coefficient of the prefabricated pier has decreased and the residual displacement has increased in the later period,the numerical change is small and the impact is not significant.(4)The seismic fragility analysis of prefabricated assembled bridge pier of wet socket connection with UHPC materials was carried out.Based on the performance-based seismic engineering theory,50 actual ground motions were selected as input,and the timehistory analysis of the seismic response of UHPC prefabricated pier with socket connection and cast-in-place pier.were carried out.The peak ground acceleration is used as the ground motion intensity parameter,the bridge pier displacement ductility coefficient and the pier bottom bending moment are the engineering demand parameters,and 100 sample pairs are formed.The linear fitting method of direct regression probabilistic seismic demand model is used to fit the above sample pairs,and the probabilistic seismic demand model is constructed.According to the regression theory,the probability seismic fragility curve is generated by the demand model.The results show that UHPC can effectively reduce the damage of the plastic hinge area of the pier and significantly reduce the lateral displacement of the top of the pier.