Effect of steel and concrete thickness on shear strength of square concrete filled double skin tubular beams

Concrete Filled Double Skin Tubular (CFDST) members are one of the most advanced forms of composite construction, consisting of two tubes, placed eccentrically or concentrically, with concrete sandwiched between the tubes. CFDST members are characterized by their increased flexural strength, improved ductility, and enhanced stiffness which render them suitable for earthquake prone regions. This paper explores the shear characteristics of square CFDST beams experimentally under the application of uniformly distributed load (UDL). Two main parameters i.e. steel thickness and thickness of the sandwiched concrete were varied, and their corresponding effects on shear strength, toughness, and ductility were investigated. It is found that decreasing the thickness of the sandwiched concrete (by increasing the dimensions of the inner tube) for the same thickness of the steel tubes decreases the shear strength of the members. On the other hand, increasing the thickness of the steel tubes for the same thickness of the sandwiched concrete increases the shear strength. Also, as the dimensions of the inner tube increases (thickness of the sandwiched concrete decreases) for the same thickness of the steel tubes, the associated energy dissipation decreases while the ductility increases.