Research On Double Plastic Hinges Of Reinforced Concrete Pier

The earthquake damage investigation at home and abroad shows that the damage failure of concrete piers is a major form of bridge damage.The damage of bridge piers will cause the collapse of the upper structure of the bridge,which will seriously hinder the post-earthquake rescue work and post-disaster recovery work.Concrete piers generally form plastic hinges at the bottom of the pier,and the rotational deformation ability of the plastic hinges has a significant influence on the seismic performance of the piers.In order to improve the inelastic deformation of the pier under strong earthquakes,this paper innovatively proposes a new type of pier with double plastic hinges failure mechanism in the lower part of the pier.The formation process of the double plastic hinge is studied by model test and finite element simulation.The main research work of the pier's seismic capacity includes the following aspects:(1)The research status of seismic damage form of concrete piers,seismic performance evaluation method and application of FRP in engineering.Based on this,a double plastic hinged concrete pier with mixed reinforcement is proposed,and the reaction frame is carried out according to the test plan.The design of the transformation was carried out,and the material properties of steel bars and concrete were measured,and the test contents and loading methods were determined.(2)Three concrete pier model specimens were designed and manufactured.The total height of the model test piece is 3.5m,the loading height is 2.7m,and the square section size is 250mm×250mm.The test piece D adopts the traditional ordinary steel bar reinforcement,and the C and E test pieces adopt the GFRP tendon and the ordinary steel bar mixed reinforcement method,wherein the height of the GFRP bars is 1m and 0.7m respectively,to study the different heights of the GFRP in the mixed reinforcement.The effect of hinge formation.(3)A pushover test was carried out on the model pier,and the crack development of the pier and the damage of the test piece during the test were recorded.The area,process and crack width formed by the plastic hinge of the pier were observed.The lateral force and the displacement data were collected.The strain,displacement and other data of the pier were collected by strain gauge,displacement gauge and NDI,and the curve of the section curvature along the pier height was obtained.(4)Combining the shear-displacement curves of each pier and the crack width along the pier height distribution curve,the curvature and the rotation angle along the pier height distribution curve,the angular ductility and displacement ductility of the single and double plastic hinges are calculated by the theoretical formula.Deformability and load carrying capacity of single and double plastic hinges.(5)Using the finite element software ABAQUS based on the PQ-fiber subroutine,the nonlinear simulation is carried out,and the pushover curve of the pier is obtained.The simulation results are basically consistent with the experiment.Finally,the biplasticity is obtained according to the distribution of the strain along the pier height.Limit strain utilization of GFRP bars when hinged.