Bending Capacity and Elastic Stiffness for a Novel Configuration of Cold-Formed U-Shaped Steel-and-Concrete Composite Beams

This paper discusses a novel cold-formed U-shaped steel and concrete composite beam (RCUCB) for which a reinforcement truss is furnished to stiffen the open steel U-section. Inverted U-shaped reinforcements are assembled to enhance the interface between a concrete flange and a beam web, which includes the bottom reinforcement, concrete fill, and steel U-section. A longitudinal bottom reinforcement is installed to control the slip between the concrete web and the steel U-section. Ten specimens were tested under bending moment, and all exhibit a typical flexural failure. Significant integrity for the RCUCB can be achieved through the enhancement of the reinforcement truss and inverted U-shaped reinforcement. A modified method for determining the shear connection degree of the RCUCB is proposed, which considers the contributions from the inverted U-shaped reinforcement, neck concrete, and reinforcement truss. Two transformed section methods were adopted to determine the elastic stiffness. In addition, a simplified bending capacity calculation method is presented.