Study On Seismic Behavior Of Prefabricated RC Bridge Piers Joined On Tenon And Mortise

In order to improve the mechanical performance and durability of the joint of precast assembled RC bridge piers,as well as improve the assembly efficiency and construction safety,a new type of assembled bridge pier joint structure,which adopts cast-in situ UHPC and mortise and tenon joint,is proposed.The pseudo-static tests of one integral cast-in-place bridge pier(ZT-1),one prefabricated RC bridge pier(CFST-1)mixed with grouting socket and steel pipe shear key,and two cast-in-place UHPC and prefabricated RC bridge pier(UT-1and UT-2)mixed with tenon and tenon joints at different joint positions were carried out.Combined with finite element expansion analysis and theoretical analysis,the restoring force model of precast RC bridge piers with in-situ UHPC and mortise and tenon joint is put forward.The main contents and results of this paper are as follows.(1)The pseudo-static test results show that the failure modes of the four members are all compression bending failure,and the failure mode of UT-2 is the same as that of the whole cast-in-place bridge pier,and the plastic hinge position occurs at the bottom of the pier,while the plastic hinge upward shift occurs in CFST-1 and UT-1.Compared with ZT-1 member,the test results of horizontal bearing capacity and seismic performance index of other components are as follows:horizontal bearing capacity of CFST-1 member increases by 1.99%,and ductility performance decreases by 28.01%.The residual displacement decreased by 72.68%,the energy dissipation capacity decreased by 39.44%,the stiffness degradation rate decreased by 3.07%,and the"pinching effect"of hysteretic curve was the most obvious.The horizontal bearing capacity of UT-1 component is reduced by 8.22%,and the ductility of UT-1component is improved by 16.98%.The residual displacement increases by 66.82%,the energy dissipation capacity increases by 38.14%,and the stiffness degradation rate increases by 1.04%.The horizontal bearing capacity of UT-2 is reduced by 4.87%,the ductility of UT-2is increased by 21.39%compared with ZT-1,the residual displacement corresponding to the ultimate displacement is increased by 67.92%,the energy dissipation capacity is increased by77.21%,and the stiffness degradation rate increases by 0.84%.(2)The finite element model established by the secondary development plug-in of ABAQUS is in good agreement with the test results.Based on the finite element model verified by the test,the parameter expansion analysis is carried out for the second type of precast assembled bridge pier(UT-2)of mortise and tenon hybrid joint.The results show that:Slenderness ratio,axial compression ratio,the main steel reinforcement ratio of mortise and tenon joint type mixed joint precast assembled piers skeleton curve features is most obvious,and the influence of other factors such as volume stirrup ratio,the influence of joint parameters is limited.(3)In the design of pier joint parameters,it is suggested that the lowest W/H ratio of the tenon width to the pier section should meet the requirements of the tenon section to withstand the pier’s own gravity and other temporary loads in the erection construction,and the maximum w/h should not exceed 0.63.The ratio of the thickness of cast-in-place UHPC to the pier height t_u/l should be selected within the range of 0.075～0.125 on the premise of meeting the requirements of the welding length of steel bar and the manual operation space.The ratio of common concrete height to pier height h_u/l can be selected in the range of 0.1～0.15..(4)On the basis of theoretical analysis,obtained the mortise and tenon joint type mixed joint precast assembled piers restoring force model of the characteristic value calculation method,the finite element model and the calculation results of unloading stiffness with regression analysis to get the stiffness fitting formula,established the mortise and tenon joint type mixed joint precast assembled piers skeleton curve model and the restoring force model.The results are compared with those of finite element calculation and experiment.The results show that under different slenderness ratio,axial compression ratio and reinforcement ratio of main reinforcement,the variation trend of the proposed skeleton curve model is basically consistent with the finite element calculation results.In addition,the restoring force model proposed in this paper is in good agreement with the experimental results,and can better reflect the seismic characteristics of the components.