Flexural behavior of U-shaped steel-concrete composite beams under positive bending

The use of cold-formed U-shaped steel and concrete composite beams has increased with the advantage of permanent steel form as a load-resisting element. In this study, a new type of U-shaped steel-concrete composite beam with a bolt connection was proposed. Four-point flexural tests of full-scale specimens were performed to evaluate the flexural behavior of the composite beams under a positive bending moment. The main test parameters were the types of U-shaped steel sections and location of the neutral axis at ultimate strength. The U-shaped composite beams under positive bending behaved similarly to the composite beams with an I-shaped steel section. The strain compatibility method is recommended to evaluate the positive flexural strength of the composite beams. In addition, the effective flexural rigidity was proposed to capture the increasing trend of the flexural stiffness ratio according to the shear span-to-depth ratio.