Numerical study of the cyclic behavior of embedded CFST columns to foundation

In this paper, a finite element analysis of the behavior of embedded CFST columns to the foundation under axial-lateral combined loading. First, the proposed finite element model is compared and analyzed by the experimental results of previous research, which showed that the local damage, failure patterns and hysteresis curves were consistent. A detailed parametric study to evaluate the cyclic behavior of embedded CFST columns to the foundation with the characteristics, the ration diameter to thickness, embedded length, compressive strength and connection conditions CFST column to the foundation. Based on the parametric study, the values of stiffness, strength, ductility and energy for the studied specimen have been calculated. The results showed that using the proposed finite element model, weak cyclic behavior for CFST connection to the foundation in the conditions of connection with the base plate and better cyclic behavior for the CFST column and its connection to the foundation in the embedded conditions is obtained. In addition, the hysteresis behavior of the CFST column connection with the embedded stiffener plate is much better than the embedded connection without the stiffener. The rings stiffener of the hysteresis diagram changes compact condition with increasing concrete strength. In addition, lateral strength, lateral stiffness, ductility performance and cumulative energy dissipation also increased in compact specimens with increasing confine concrete. The failure modes of the CFST connection to the foundation with the base plate are the same as the embedded connection mode without the stiffener and with the ring stiffener. The failure modes in these three modes are from the connection as a tearing steel pipe at the end of the column. In the case of an embedded connection with a longitudinal stiffener, it is a diagonal crack of the concrete on the foundation. Lateral strength, lateral stiffness, ductility performance, and cumulative energy also increase with increasing steel pipe thickness. CFST column burial conditions with hardeners have a positive effect on the hysteresis rings of CFST connection to the foundation, and this type of connection has been able to significantly improve lateral strength, lateral stiffness, ductility and dissipative cumulative dissipation energy.