Study On The Construction Joint Modeling And Influence To Seismic Behavior Of RC Frame Structure

Construction joint is inevitable in the cast-in-situ RC structure. Much tests have been done and found that the tensile strength of concrete across construction joint are much weaker than integral concrete, and it could barely resist shear stress if there were not special managements. Seismic damages around construction joints appeared in some RC components, especially columns of frame structure, which illuminates that construction joint may be a potential vulnerable point where a sliding failure developed. But the insufficiency is that most of the research is aimed at joints between existing and newly placed concrete, irrespective of dowelling action of the main reinforcement passing through the joint. And there are few of publication on mechanics or numerical model describing the seismic behavior of construction joint, which is necessary for a new nonlinear analysis method of RC structure taking joints into account. There is no criterion about how to consider the impact of construction joint in RC frame structure. The paper focuses on force transferring mechanics between joint through experimental research, the mechanical properties of construction joints and its affects on the seismic properties of RC component were studied, based on the experimental data and theoretical analysis,the numerical model of construction joint is established. Then apply the numerical model to the RC frame structure nonlinear analysis, the influence laws of construction joints on seismic performance of RC frame structures were studied,and the range of considering the effect of construction joints were defined, finally the corresponding design suggestions were given.The main contents of this paper as following:①Through the uniaxial compressive strength test,uniaxial tensile strength test and direct shear test of short rectangular beam,the basic mechanical properties of construction joint were studied. The contribution of lengthways reinforcements passing through the joint to mechanical properties of construction joint is researched by theoretical analysis. Through comprehensive analysis of construction joint of two component and their commitment to the role of the tangential force and the normal force, the force transfer mechanism of construction joint is cleared.②In order to study the influence of construction joint on seismic behavior of RC member, a serious of cantilever columns were tested under cyclic loading. The destruction of test specimen configuration, vertex load-displacement hysteretic curve, bearing capacity, deformation, energy dissipation capacity, strength reduction, stiffness degradation, reinforcement strain, a column bottom longitudinal slip, plastic hinge zone, shear deformation and bending deformation were analyzed based on the experimental study. Combined with the experimental data and theoretical analysis, the hysteretic shear model of RC member with construction joint were proposed.③By test results and theoretical analysis, the stress characteristics and transmission mechanism of construction joint are further clarified, then the model of construction joints is established. On this basis, a fiber line element model is derived which can be used to simulate the columns with construction joint. Finally, the new model is verified correctness through the OpenSees software. The model can be used in nonlinear analysis of reinforced concrete structure simulation of construction joint.④The influence of construction joint to seismic behavior of RC frame structures in different earthquake intensity regions was analyzed. Furthermore, analysis was continued in-depth considering the varying axial force. Then nonlinear numerical analyses of RC frame structures are done on the same intensity in different aspect ratio. The influencing factors were screened,and the influence laws of construction joints on seismic performance of regular RC frame structures were concluded.⑤Defining the scope of considering the effects of construction joints in the seismic design of regular RC frame structure. Then the simplified seismic design suggestions are putted forward from aspects of concept design, analysis method and control measures.