Cyclic Performance Of Concrete-Filled Steel Tubular Columns After Exposure To Fire

The strength of concrete and steel decrease a lot after exposure to fire. As a result, the seismic performance of concrete-filled steel tubular (CFST) columns may be changed. It is important to analyze the cyclic performance of this kind of column after fire. However, few research studies have been dealt with in this area in the past.In this paper, cyclic behaviors of CFST columns after fire were investigated. The main achievements can be summarized as follows:(1) Experimental studies on the behavior of CFST columns were carried out, including seventeen monotonic specimens and forty-three cyclic beam-column specimens. These specimens were heated following as closely as possible the ISO-834 standard fire curve or the standard fire curve prescribed by the Regulation of GB/T 9978-1999 (Structural Member Fire-Resistant Experimental Method). The parameters in the study included the fire duration time, the axial load level, the section type and the strengthen method. The ultimate lateral strength, flexural stiffness, dissipated energy and ductility of the columns were compared and analyzed. (2) Based on the stress-strain relations for steel and concrete after high temperature and the temperature field in the structural member, fiber-based model was developed to calculate the hysteretic moment (M) versus curvature (φ) relations and the lateral load (P) versus lateral displacement (?) relations. In this model, force-temperature-time path was considered. The results from the fiber analysis of the composite specimens compared favorably with the experimental results.(3) Using the finite element program ABAQUS/Standard 6.4, theoretical model was built to analyze the load versus deformation relationship curves. Furthermore, the stress distributions in the core concrete during the loading, the composite interaction between the steel tube and the concrete were studied. These analysis processes were carried out under two different conditions, namely at the ambient temperature and after exposure to fire. Based on the analysis, the mechanism of CFST columns after exposure to fire was investigated.(4) Influences of parameters on the behavior of the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (?) relationship such as fire duration time, axial load level, slenderness ratio, steel ratio, steel yielded strength and concrete...