Research on Quasi-Static Test for Cast-in-Place UHPC Joints in Precast Segmental Pier and Heights of Cast-in-Place Joints
A group of precast segmental pier specimens(precast pier for short)and a group of cast-in-place pier specimens(CIP pier for short)were prepared for quasi-static tests,to investigate the seismic performance as well as the plastic hinge transfer mechanism of the cast-in-place UHPC joints in the precast segmental piers.The issues analyzed include the failure modes,hysteresis characteristics,stiffness degradation feature,energy dissipation capacity,residual deformation and curvature distribution.The finite element models of the precast piers with cast-in-place UHPC joints with heights of 1.0,0.6,0.5,0.4,0.3,0 m,respectively,were established in OpenSees,to study the influence of heights of cast-in-place UHPC joints on the seismic performance of precast piers,and on the basis of which the method to calculate the limit heights of cast-in-place joints is proposed.The results demonstrate that the damages in precast piers concentrate in the joints,being the opening and closing of joints,but no obvious damages appear in UHPC zone,and the break-off of the longitudinal prestressing tendons is a signal of the load bearing capacity loss.The load bearing capacity and pier-top ultimate horizontal displacement of the precast pier are 1.25 and 1.12 times of those of the CIP pier,respectively,while in terms of ductility,energy dissipation and pier-top horizontal residual displacement,the two types of piers are roughly the same.Due to the occurrence of cracks in the UHPC interface,the initial stiffness of precast pier is only 65％of that of the CIP pier.The heights of cast-in-place UHPC joints dictate the failure modes of the precast pier,which have a limitation.If the height of a cast-in-place UHPC joint is less than the limit value,the plastic hinge in a precast pier will shift.The method proposed to calculate the limit heights of the cast-in-place UHPC joints can guide the design of the precast pier,the limit heights of cast-in-place UHPC joints is not only related to the flexural strengths of both the RC and UHPC interfaces,but also directly proportional to the height of the pier.
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