The Research On The Seismic Performance Of Fully Jointless Semi-integral Bridges

China is a country with serious earthquake disasters in the world, strong earthquake is easy to lead a bridge to damage and bring huge economic losses. Many earthquake disasters and a lot of seismic research has shown that:jointless bridge is a small and medium bridge with excellent seismic performance and belongs to the "seismic structural system". The research team of hunan university has proposed a Fully Jointless Semi-integral Bridge (FJSBs, hereinafter referred to as "Fully jointless bridges") with more excellent performance than the integral abutment Bridges. After ten years of research and practice, although the completed conventional design and construction method of FJSBs has been established, but its excellent seismic performance has never been analyzed and evaluated. In order to complete "The Research on the Seismic Performance of Fully Jointless Semi-integral Bridges ", the main work in this paper is as following:(1) Study the elastoplastic tensile mechanical properties of the reinforcement approach pavement. Based on the axial average stress-strain relationship of reinforcement and concrete, the theory skeleton curve model of tensile force-deformation is derived by analytical method and use the Matlab edite the nonlinear solver. An 1:1 full scale indoor model test is carried out to study on the elastoplastic tensile properties of the approach pavement and compared with the analytical theory. Based on the elastoplastic tensile theory model of the approach pavement, a parameter sensitivity analysis is carried out, which lead to a more comprehensive understanding the pavement mechanical characteristics. Determine the performance points, define the damage index and propose a simplified multi-linear model.(2) Study the refined finite element model of the approach pavment system. The simulation of the approach pavement system is complex, involving ground beam-soil interaction, axial-bending-shear reinforced concrete approach pavement and interface friction effect between the subgrade and approach pavement. Review and analysis the macroscopic model, the truss model, microscopic model and (shear) fiber model which are suitable for simulation of the axial-bending-shear characteristics of reinforced concrete wall/panel; determine the suitable model which can discribe characteristics of the approach pavement. The 3D element equations of the sectional shear fiber model are derived and the parameters of the cross sectional shear model is also expounded. The approach pavement model is established by the OpenSees software. Earth pressure models of rigid retaining wall which are suitable for ground beam-soil interaction have carried on the comprehensive analysis. The EHFD model which can adapt to the wall height changes is selected as the ground beam-soil interaction analysis model, and the OpenSees is used for modeling.(3) Study the dynamic characteristics and seismic response sensitivity parameters of the fully jointless semi-integral bridge. Establish the fully jointless semi-integral bridge and continuous girder bridge as a 3D elastic finite element model. Modal analysis method is used and the dynamic characteristics of the fully jointless Bridge and continuous girder bridge are compared. Do the sensitivity analysis using the response spectrum method with the different parameters such as approach pavement stiffness, bearing stiffness, height of piers, bridge lenght, oblique Angle parameters, and give the corresponding design suggestions, respectively.(4) Study and propose seismic construction measures for the fully jointless semi-integral bridge. Based on the refined finite element model of pavement system, the 3D nonlinear finite element model of the FJSBs is established. Select suitable typical seismic waves for nonlinear time history analysis and subsequent vulnerability analysis. In order to enhance the seismic capacity of the FJSBs, the bridges with 1 and 2 ground beams are carried on nonlinear time history analysis under 8 degree and 9 degree seismic intensity. Also, in order to enhance the seismic capacity of the FJSBs in the transverse direction, different bearing stiffness and lateral clearance of the stop-girder are analyzed in the schedule. According to the characteristics of the fully jointless semi-integral bridge, two retaining walls are integrated with the sleeper beam at the both ends, through the interaction between retaining wall and soil increase the transverse stiffness of the approach pavement system. Parameter analysis is carried out to determine the retaining wall sizes under earthquake loads. Suggest the construction sizes for the new type sleeper beam.(5) Analyze and evaluate the vulnerability of the fully jointless semi-integral bridge. Present the displacement-based damage indicators of the bearing, ground beam and approach pavement. Based on the different earthquake intensity, both the fully jointless bridge and continuous girder bridge are carried out with incremental dynamic analysis (IDA), to get a sufficient number of earthquake response values of each component. Linear fitting the data to get the demand probability model. Under the damage index and demand probability model, the vulnerability curves of components with damage status of all levels can be obtained and the first-order boundary method is adopted to get the bridge system vulnerability curves. Through the analysis of vulnerability curves and seismic assessment under various seismic intensity, master the seismic performance of the fully jointless semi-integral bridge.