Designing thin-walled composite-filled beams

Thin-walled composite-filled beams consist of a cold-formed open steel box section with an infill of concrete. The strength of such beams is limited by the compression buckling capacity of the steel plate at the top of the open box section. Enhancement of strength is possible by stiffening the compression steel plates at the open end of the box section with various modes of interface connections or strength-enhancement devices. In this paper, the effect of various strength-enhancement devices is correlated to the generation of shear bond between steel and concrete using both experimental and design-oriented analyses. Flexural capacity of such beams can be derived based on either yielding or buckling of steel depending on the generated steel–concrete interface shear bond simulating full or partial shear connections. Design equations are developed and their performance is validated through test results of 24 experimental beams with five different modes of strength-enhancement device. Design procedures for such beams are illustrated with calculated design examples. Such simple design procedures can be adopted in the actual design of thin-walled composite beams with various modes of strength-enhancement devices in practical applications.