Inelastic behavior of circular concrete-filled steel tubes: monotonic versus cyclic response

In this paper, a computational procedure for determining the response of circular concrete-filled steel tube (CFT) columns to monotonic loading is developed. Firstly, the basis of the proposed method is established by creating accurate three-dimensional nonlinear finite element models of these columns, which are validated by comparing their response results with those of experimental tests that are available in the literature. Then, these models are used for an extensive parametric study that determines the response to monotonic lateral loads of 192 circular CFT specimens with fairly broad values of diameter-to-thickness ratios, yield stress of steel tube, compressive strength of concrete core and axial load levels. On the basis of this response databank, empirical expressions are developed to estimate the force–displacement behavior of circular CFT columns under monotonic loading with simple yet reliable manner. The validity of these empirical expressions is verified by comparing their results with those of experimental tests. It is found that the proposed expressions can effectively describe the force–displacement behavior and capacity of circular CFT columns under monotonic loading conditions. These expressions are also used in pushover analysis of a simple frame consisting of steel beams and CFT columns in order to demonstrate their applicability and usefulness in simple practical problems. Finally, the proposed method, of determining the response of composite structures to monotonic lateral loading is compared with nonlinear time-history response analysis of these structures and useful conclusions are provided.