Development and validation of fiber model for high-strength square concrete-filled steel tube beam-columns

This paper presents the development and validation of a general fiber model that can be used to predict the monotonic and cyclic force-deformation behavior of high-strength square concrete-filled steel tube (CFT) beam-columns. The paper also presents a general analytical approach for developing the critical input parameters for the fiber model, that is, the stress-strain (sigma-epsilon) curves for the fibers modeling the CFT cross section. This general approach develops the fiber sigma-epsilon curves analytically from the results of a three-dimensional nonlinear finite element analysis of a corresponding CFT segment. The CFT fiber model and the analytical approach for developing the fiber sigma-epsilon curves are validated using experimental results from 26 high-strength square CFT beam-column specimens tested under combined a-vial and monotonic or cyclic flexural loading in the U.S. and in Japan as part of the U.S.-Japan Cooperative Earthquake Research Program, Phase V.