Numerical Study on Behavior of K-joints of Concrete-filled Steel Tubular

The main role of connections, the transfer of forces between structural members and maintaining the integrity of the structure under the influence of load loads. Many structural failures are not simply due to defects in the design and analysis of structural members, but rather due to the non-respect of the behavior and design of joints. Even when member structures of the structure are accurately known, there is no complete understanding of the behavior of the joints. For this reason, in this research, a K-shaped connection under the uniform load loading model was modeled by Abacus software and validated by the results of previous research. Then, 8 numerical analytical models with different variables including steel yielding stress, compressive strength of concrete, angle of the steel tube and the presence of a stud have been developed to predict different characteristics of the responses. Their overall results indicated that the use of flint glass in the main pipe, which was filled with concrete, increased the stress intensity of the steel materials and the compressive strength of the filler concrete. An increase of 25% and 50% of the subsidence stresses of the secondary steel pipes increased the final bond strength by 22.9% and 74.6%, respectively, and the strength of the aggregate increased by 24.9% and 52.1%, respectively. The reduction of the angles between the sub-tubes and the main pipe in the K-shaped steel pipe connection showed that by decreasing the angle between the sub-tubes and the main pipe, the final quantity and initial hardness decrease, but the structural ductility increases. In general, it can be concluded that increasing the subsidence tension of the sub-tubes has the greatest effect on improving the behavior of the K-shaped joint, which, in addition to increasing the final load and the formability, also increased the initial hardness of the load-displacement curve. In contrast to the increase in the tensile strength of the main steel pipe, the final load and bond strength were reduced due to the simultaneous loading of the sub-channels and only increased the initial hardness to some extent.