Experimental Study On Seismic Performance Of Precast High-speed Railway Bridge Piers

The whole-span prefabrication,prefabricated T-beams and box girders have been widely used in the superstructure of high-speed railway bridges,while piers are usually cast in place.In order to promote the application of precast piers in high-speed railway bridges,a new type of grouting sleeve using UHPC as grouting material is proposed in this paper.Four precast piers and one cast-in-place pier were used to conduct pseudo-static tests.Experimental analysis,theoretical calculation and numerical simulation are conducted to study the seismic performance of precast high-speed railway bridge piers.The main research contents are as follows:(1)Research on UHPC grouting sleeve connection performanceA new type of sleeve with high strength bolt was developed to improve the mechanical occlusion between the sleeve and the grouting material.UHPC was used as the grouting material.The reliability of the new sleeve was verified by unidirectional tensile test of UHPC grouting sleeve connection specimens.Experimental parameters include anchorage length,loading age,grouting defects,eccentric placement of steel bar and number of high-strength bolts.The strength development law of UHPC grouting material was explored through material performance test.The critical anchorage length required of the new sleeve is explored by adjusting the anchorage length of the steel bar(5d/6d/7d/8d),and the influence of construction defects on the bearing capacity of sleeve connectors was explored by setting grouting defects and reinforcement eccentricity.By changing the number of high strength bolts,the contribution of high strength bolts to improving the mechanical occlusion of the interface between grout material and the inner wall of the sleeve was verified.(2)Cyclic loading experimental research on precast high-speed railway bridge piersFour precast piers and one cast-in-place pier were used to conduct pseudo-static tests to verify the reliability of the connection form and to study the seismic performance of precast high-speed railway bridge piers.The connection forms of precast pier specimens are UHPC grouting sleeve,UHPC grouting sleeve with post-tensioned prestress,UHPC grouting bellows,and UHPC grouting bellows with post-tensioned prestress.The pseudo-static test results of precast piers were compared with those of cast-in-place pier,and the effects of different connection forms on the seismic performance were studied,such as failure mode,hysteretic characteristics,stiffness characteristics,energy dissipation capacity,displacement ductility and residual deformation.The effects of post-tensioned prestress on the initial stiffness,horizontal bearing capacity and residual deformation of precast piers were studied,too.(3)Research on numerical simulation method of grouting sleeve connected precast bridge piersBased on the Open Sees computing platform,a finite element model of precast piers connected by grouting sleeve is established using beam with hinges element.Considering the contribution of sleeve stiffness,the damage of precast pier is more concentrated,so the length of traditional plastic hinge is reduced.Proposed a method to establish the equivalent material constitutive relationship of the unbonded longitudinal bars to consider the softening effect of unbonded bar,so as to establish an equivalent fiber section that satisfies the plane section assumption.The full section stiffness of the bridge pier is reduced to obtain the effective section stiffness to consider the influence of shear deformation and longitudinal reinforcement slip.The finite element model of the precast bridge piers was verified by the results of the pseudo-static test.