Research On Mechanical Behavior,Performance Improvement And Calculation Method Of Plastic Hinge Zone In The Precast Concrete Shear Walls

Due to the high lateral stiffness of shear walls to resist wind and earthquake action,it is effective to use the shear walls for buildings as the first lateral load resisting system.As a development direction of the new construction industry,many researchers have made a great deal of studies on the implementation of precast concrete constructions.The key of the seismic performance of precast concrete shear walls is the connection of the joint.In addition,with the development of steel smelting technology,the application of high strength reinforcement in architectural engineering is increasing gradually.Considering the above situation,supported by National “thirteenth five-year” plan for research and development and the previous National “Twelfth Five-Year” Plan for Science and Technology,this paper dedicated to study the pure shear and flexural shear performance of precast concrete shear wall joints,seismic performance of precast shear walls with conventional grouting coupler or unbonded post-tensioned prestress high reinforcement,and put forward the corresponding theory or calculation method.The main work is drawn as follows:1.The seismic performance of the precast concrete shear wall with conventional grout-filled pipe splice is studied,and the effect of the grout sleeve on the deformation of the plastic hinge is studied.For this purpose,four full-scale shear walls are designed where one of them was cast-in-place and others were precast.The bed mortar of the joints of the precast specimens was using solid concrete(grouting one by one)or polymer concrete and high strength grouting materials(grouting together with plug)respectively.In addition,one of the precast specimens' reinforcement had an unbounded segment in the base in order to increase the deformation and energy dissipation capacity of the structure.Based on the experimental results of precast concrete shear wall structure with grout sleeve,their failure mode and damaged process,crack crack model and hysteretic performance,energy dissipation,stiffness degradation,and curvature distribution at the bottom of shear wall(the plastic hinge region)were studied.The results show that the shear wall with high strength of bed mortar has good seismic performance;however,its initial stiffness,cracking load and ductility coefficient are still slightly lower than that of cast-in-place member.2.The pure shear performance of the precast joint was studied.The parameters of the test specimens included the joint form(flat and shear key joints),the number of the shear keys.The difference of bearing capacity between dry joint and epoxy glue wet joints,and the influence of high strength and lateral force on the joints were also studied.The shear bearing capacity and stiffness of the joints are obtained in the tests.Their bearing capacity was calculated and analysed throuth AASHTO Standard,Rombach's suggestion formula and Technical Specification for Precast Structure.And then,sevral formulas for calculating the shear capacity were proposed according to the experimental results.3.For the common crack patterns of concrete,a concrete cracking model of pure aggregate interlock was presented by taking into account the equilibrium of forces,geometric compatibility equations,and constitutive relationship.Then,according to the local stress field model of the reinforced concrete at the crack interface,the relationship between the axial direction and the dowel action and the uniform stress was obtained.Then,the equations of the bond slip and dowel action and aggregate interlock are combined through the geometrical relationship of crack deformations.Finally,the proposed concrete model was validated by comparing the calculated results with the tested results conducted by Walraven.4.Several precast beams,which would damaged in shear and flexural modes,were designed and manufactured to simulate the stress patterns of the precast shear wall joints.The beam test was four-point loading.The epoxy glue and shear keys were used in the joints.The reinforcement types of test specimens included ordinary reinforcement,non-prestressed high strength reinforcement,and prestressed high strength reinforcement.The mechanical properties of such precast joints under the conbined maximum shear force and maximum bending moment were studied.Then,this article discussed their damage process and failure mode,load and failure mode,load-deflection curve and the local deformation behavior of damage area under static.Moreover,the influence of prestress on the shear strength of specimens was also discussed with the test results.5.Based on the pure shear and flexural-shear tests of the precast joints and the potential problems of precast shear wall with conventional connection,the seismic performance of precast concrete shear walls with small prestressed high strength reinforcement under low cyclic loading was studied to improve the performance of the structure.The test specimens having the same size included one cast-in-place specimen,three precast specimens that were using ordinary reinforcement,non-prestressed and prestressed high strength reinforcement which strength grade was grade 630 MPa.Epoxy glue shear keys were adopted in the bottom joint of precast wall to improve their mechanical properties.The influence of the high strength reinforcement on the bearing capacity of the shear wall components,crack model,ductility,hysteretic property,energy dissipation,stiffness degradation of the structure and shear wall plastic hinge distribution,etc,were discussed,and then were compared with common reinforced precast and cast-in-place concrete shear wall,respectively.6.A three-strut-and-tie model was proposed according to the above test specimen dimension to calculate the strength of the shear wall structures.Then,the calculation and analysis process of the standard strut-and-tie model was presented in the case of considering the strength of confined concrete.At the same time,the diffusion of the pressure in the bottle-shaped strut was studied by the method of isobaric line of the pressure,and the distribution of transverse stress of isobars was obtained.Finally,according to the characteristics of the shear wall,the transverse tension of the diagonal strut in the shear wall and the tensile reinforcement ratio were analyzed.7.A series of calculation process of load-displacement behavior for reinforced concrete shear wall with different connection forms(cast-in-place and precast)was proposed in this paper.The lateral deformation caused by the bending of shear wall,the shear and the reinforcement slip was calculated separately,and the interaction between them was considered by the compatibility and other conditions.The bending deformation behavior was mainly analyzed by the traditional fiber model.Shear deformation was mainly based on the modified compression field theory(MCFT).Their interaction was considered by the combination of the three springs.In addition,a method for calculating the plastic hinge length was proposed based on the fracture energy of the material,and the plastic hinge length of the structure was derived from the energy balance.For the shear walls with lap-spliced bars,a simple way to deal with the lap splice was proposed to deal with the complex mechanical behavior and deformation of the lap splice in the plastic hinge region.Finally,the deformation property of shear walls with grout sleeve and small prestressed high strength reinforcement were studied.Based on bilinear elastic model,the equivalent stress-strain constitutive relationship of grout sleeve was put forward,which is used to simplify the lateral deformation of the shear wall.The validity of above mentioned model or analysis process was confirmed by comparing the analytical results and experimental results.