Structural Improvement And Seismic Performance Analysis Of Precast-assembled Concrete-filled Steel Tube Pier

At present,prefabricated segmental piers are mostly used in high-speed road bridges and canal bridges in low seismic area.The reason is that these projects have higher requirements for construction environment and time limit,and it can give full play to the advantages of factory prefabrication.During the earthquake,the damage at the bottom joint of the assembled bridge pier is serious,the poor energy dissipation performance and the high displacement demand of the pier top limit the popularization of it in the middle and high seismic area.In this paper,the concrete filled steel tube pier is adopted to solve the problem of serious damage at the bottom joint of the segmental assembled pier.In order to improve the energy consumption of the structure and reduce the displacement of the pier top,a new type of stop bolt damping device for energy dissipation is proposed to set between the segments and bottom of pier.In addition,the study of this type of pier has the limitation of the size at present,thus the seismic response under the actual structure size is further studied here.In order to avoid the falling beam risk of this kind of bridge structure during strong earthquake,a method of controlling the top displacement of fixed pier by using anti-falling beam device and this stop bolt device is put forward.The main contents of the study are as follows:(1)According to the structural characteristics of concrete filled steel tube(CFST)pier,the theoretical basis and calculation method suitable for the research object in this paper are determined.The numerical model of the corresponding specimen in the relevant literatures was established by Opensees,and the reliability of the modeling method was verified by comparing the results.(2)The pseudo-static analysis is carried out after installing the stop bolt device.By comparing the pseudo-static performance of the whole reinforced concrete bridge pier,the concrete filled steel tubular pier and that with the stop bolt,The influence of additional stop bolt on the seismic performance of concrete-filled steel tube pier and the difference of seismic performance between the segmental pier and the cast-in-place reinforced concrete pier are analyzed.(3)The whole substructure design of segmental concrete filled steel tube pier bridge system is described,including the section size of pier,axial compression ratio,prestressing force and the arrangement of stop bolt,etc.The seismic behavior of concrete filled steel tube pier with different dead load axial compression ratio,prestress,slenderness ratio and limited tension bar is studied by pseudo static method.The design of the pier is optimized according to the analysis results.(4)The models of continuous beam bridges with segmental concrete-filled steel tube piers and the whole reinforced concrete piers are established respectively.Then,the damping effect of the segmental concrete-filled steel tube piers with stop bolt is studied and the seismic response of the whole reinforced concrete piers is compared with that of the segmental concrete-filled steel tube piers.In the case of strong earthquake,the effect of controlling the top displacement of fixed pier is analyzed by combining the stop bolt with the longitudinal cable limiter which is installed between pier and the end of girder.Through the above research,it is found that the new stop bolt device proposed in this paper can not only obviously improving the energy dissipation capacity of the segmental assembled steel tube concrete pier but can also greatly reducing the displacement demand of the pier top during the earthquake,and it is of good repair property after the earthquake.In addition,the combination of anti-fall beam limiter and the stop bolt in the high seismic area can effectively avoid the risk of girder falling.