Experimental Behavior of High Strength Square Concrete-Filled Steel Tube Beam-Columns

Abstract

The flexural force-deformation behavior of high strength square concrete-filled steel tube (CFT) beam-columns was experimentally investigated. The parameters in the study included the width-to-thickness $(b/t)$ ratio, the yield stress $\left({\sigma }_y\right)$ of the steel tube, and the axial load level. Eight CFT beam-column specimens were tested under constant axial load and monotonically increasing flexural loading. The CFT specimens were 305-mm square tubes with nominal $b/t$ ratios of 32 or 48, made from either conventional (A500 Grade-B) or high strength (A500 Grade-80) steel, and filled with high strength (110 MPa) concrete. Experimental results indicate that the moment capacity of CFT beam-columns is reached as inelastic behavior of the steel tube and concrete infill is combined with local buckling of the steel tube and crushing of the concrete. The moment capacity of high strength square CFT beam-columns can be predicted with reasonable accuracy using the current American Concrete Institute code provisions for composite columns. The curvature ductility of high strength square CFT beam-columns decreases significantly with an increase in either the axial load level or the $b/t$ ratio of the steel tube. The yield stress of the steel tube does not seem to have a significant influence on curvature ductility.