Composite Flexural Behavior of Full-Scale Concrete-Filled Tubes without Axial Loads

Abstract

Most prior experimental research on the composite behavior of concrete-filled tubes (CFTs) in flexure has been performed using minimodels. The conclusions that have been reached based on the prior research stipulate that the interaction between the concrete and the steel is maximized by steel tube walls confining the concrete, rendering the addition of shear connectors unnecessary. The goal of the current study is to examine the composite flexural behavior of full-scale CFTs, which could be used in actual construction. Four, full-scale, 20-ft- (6-m)-long simple-supported CFT beams were tested under four-point loads. Two were rectangular with a width of 12 in. (305 mm) and the other two beams were circular with a diameter of 18 in. (457 mm). Load, deflection, steel strain, and concrete movement were digitally recorded, and the concrete cracks in each section were mapped and photographed. Test results showed that composite action was improved by shear connectors particularly for circular CFT beams and that the AISC nominal moment capacity prediction was not conservative for circular CFT beams without shear connectors.