Nonlinear inelastic time-history analysis of rectangular concrete-filled steel tubular frames using a fiber beam-column element

In this paper, a new simple and effective numerical method is proposed for the nonlinear inelastic time-history analysis of rectangular concrete-filled steel tubular (CFST) frames under dynamic loadings. For this proposed method, a fiber beam-column element is formulated by considering both geometric and material nonlinearities. The geometric nonlinearities are specifically taken into account utilizing the geometric stiffness matrix and stability functions. The element stiffness matrix is assessed based on uniaxial nonlinear hysteretic material models for the steel and concrete fibers on monitored cross-sections along the element length. Furthermore, the residual stress is considered as the initial stress in the steel fibers as well. To solve the differential equation of motion of the structural system subjected to the earthquake loadings, the Newmark's average acceleration method is incorporated with the Newton-Raphson iterative scheme. Five numerical examples of the rectangular CFST column and frames with gradual increasing complexity subjected to four different earthquake loadings are analyzed and compared with results obtained from ABAQUS. The outstanding advantages of the proposed method over ABAQUS in modeling and analyzing are obtained with the highly accurate predicting the dynamic behavior of the rectangular CFST structures and the computational efficiency by using only one element per member.