Flexural properties of concrete-filled, double-skin, square-hollow-section tubular beams

Concrete-filled double-skin tubular beams consist of two tubes, placed eccentrically or concentrically, with the hollow space between the two tubes filled with concrete. This type of construction can thus combine the properties of steel and concrete to provide the advantage of increased strength, ductility, stiffness and economy of the section. This paper reports on a study into the flexural properties of beams made of square hollow section steel for the both inner and outer tube, connected with steel strips. In total, 12 specimens were tested under monotonic and cyclic loading. The effects of the concrete infill, the eccentricity of the inner tube, the provision of minimum steel reinforcement and slip control due to the attachment of steel strips at the end of the beams were studied. Beams with an eccentric inner tube showed better flexural response and were also more economical due to the reduced concrete volume; their load-carrying capacity under cyclic loading was less than that under monotonic loading. Compared with beams without longitudinal reinforcement, the beams with longitudinal reinforcement showed improved flexural strength when subjected to cyclic loading.