Study On The Mechanical Behavior Of The Joint Transferred From Two Inclined CFST Columns To A Supporting CFST Column Under Vertical Compressive Load

The development of function and structure form for tall or supper tall building has a tendency of diversification, which results to the wide application of transfer story in practical engineering. With the advantages of transmitting force directly, higher bearing capacity, smaller section, better service space, significant economy benefit and so on, the inclined column-shaped transfer structures with concrete-filled steel tubular(CFST) members have wide application prospect. Using the CFST joints and CFST column-steel beam joints for reference, a new constructional measure of the joint transferred from two inclined square CFST columns to a circular supporting CFST column was proposed. These joints were designed to connect with steel beams, and strengthen rings as well as ribbed slabs were set in the joints. Vertical compressive experiments of these joints were carried out, and further research was done through finite element analysis(FEA) software ABAQUS. In addition, the load transfer mechanisms and bearing capacities of these joints were studied. The results of this study can provide significant academic value for perfecting the theoretical research system, about the mechanical behavior of the joint of CFST structure under complex load conditions. Meanwhile, it also provides theoretical basis and design reference for engineering.The main jobs finished in this study are as the following aspects:(1) Eight specimens with different parameters were designed and conducted to vertical compressive experiments. Experiment results indicate that the design principle of “strong-joint and weak-member” can be met when the joints were designed reasonably. The failures of the specimens are due to the axial compressive damages of inclined columns or supporting column. Moreover, becaure of the setting of strengthen rings and ribbed slabs, the core zone of these joints would not destroy. The thickness of steel tube in inclined columns has great influence on the failure position and bearing capacity of the specimens. Similarly, the bearing capacity of the specimens increase with increasing insertion depth of inclined columns or the setting of stiffeners in intersecting zone of inclined columns.(2) Finite element model(FEM) was established in FEA software ABAQUS to simulate experiment condition. By comparing the analysis results with experiment results, it could be founded that the FEM can predict the bearing capacity and stress distributions of the specimens exactly, and the FEA method was verified to be feasible and reasonable. In addition, the influences on the failure modes and bearing capacities of the specimens were studied by utilizing FEA method, and the corresponding quantitative calculation method was proposed for the specimens of this study.(3) Based on the experiment results and FEA results, the failure modes and load transfer mechanism of the models were studied. The bearing capacities of inclined columns and supporting column could be calculated by the code formulas. Furthermore, the bearing capacity calculation formula for these joints was derived by using the theory for confined concrete, and a suitable design method of this kind of joint was proposed. Through the comparison of calculation results with experiment results, it can be proved that the proposed method can forecast the bearing capacity of the model accurately, and the calculation results have some safety reserve.