Seismic behavior and modeling of high-strength composite concrete-filled steel tube (CFT) beam–columns

Abstract The behavior of square concrete-filled steel tube (CFT) beam–columns made from high-strength materials was investigated experimentally. The effects of the width-to-thickness ratio, yield stress of the steel tube and the axial load level on the stiffness, strength and ductility of high-strength CFT beam–columns were studied. Sixteen three-quarter scale CFT specimens, which included eight monotonic beam–column specimens and eight cyclic beam–column specimens, were tested. The experimental results indicate that cyclic loading does not have a significant influence on the stiffness or strength of CFT beam–columns. However, it causes a more rapid decrease of the post-peak moment resistance. The moment capacity of high-strength CFT beam–columns can be predicted with reasonable accuracy using the American Concrete Institute (ACI) code provisions for composite columns. Fiber-based models were developed for the CFT beam–column specimens. The uniaxial stress–strain curves for the fibers were derived from three-dimensional nonlinear finite element analyses of the CFTs. The results from the fiber analyses of the monotonic and cyclic beam–column specimens compare favorably with the experimental results.