Research On Behavior Of Mesh Reinforcement Confined Joint Of Rectangulure Concrete Filled Steel Tabular With Discontinuous Column Tube At Joint Zone Under Axial Compressing

Concrete Filled Steel Tubular (CFST) is widely used in design and construct of tallbuildings since each material is used to take advantage of its best attributes. The CFSTcolumns are often connected with RC beams in the construction in our country. However thestudies on square and rectangular CFST column-RC beam joint are still not enough and lacksof systematic. Based on the study of circular CFST column-beam joint with discontinuoussteel tube in joint zone a new type of rectangular joint is presented in this paper. The mainfeature of this joint is that the steel tube is discontinued at the joint zone, and the column tubeis separated in each floor. As a result, the longitudinal reinforcement bars of the beam arecontinued at the joint zone, which leads to a good performance of conducting the moment andshear force of the beam. The joint is enlarged and the horizontal mesh reinforcements are usedto strengthen the joint zone.This paper studies on the axial behavior of the joint and the following works aresubmitted:1) Experimental studies were carried out with11square and22rectangular specimens toinvestigate the axial and eccentric mechanical behavior of this type of joints. The parametersof the specimen include the dimension of the joint, the size of the CFST column and the meshreinforcement ratio. The failure mode, the ultimate capacity and the deformation of eachspecimen has been studied, and the influence of each parameter has been analyzed. Theresults show that, under the confinement of the mesh reinforcement, this type of joint has highcompressive capacity and ductility. The specimens have a ductile failure mode. Among theparameters, the height of the joint, the mesh reinforcement ratio and the aspect ratio ofcolumn have significant effects on behavior of the joint.2) The linear finite element method was adopted to study the stress distribution in thejoint zone when the joint is elastic. Parameter analysis was used to analyze the influence ofeach parameter on stress distribution in the joint zone. The numerical results are consistentwith the experiment. The nonlinear finite element model of the specimen was conducted andwas validated by comparison with the test results. The nonlinear finite element analysis can well simulate the deformation, bearing capacity, crack development and the strain of the meshreinforcement.3) Based on previous study and the experimental study in this paper, a preliminarydiscussion on failure mechanism of the new type of joint was made. The formula forcalculating the ultimate capacity of axial loading is set up based on the theory of localcompression of concrete and the theory of confined concrete.The formula has good precisionin experimental environment.