Behaviour of grout-filled double skin steel tubes under compression and bending: Experiments

The grout is often used to fill the gap between two tubes as binding material in some specific structures, which may actually form a grout-filled double skin steel tube. However, little literature has been found regarding the behaviour of the grout-filled double skin steel tubular (GFDST) member, while the influence of the in-filled grout could be underestimated in the steel-grout composite structure. This paper thus presents an experimental investigation of the compressive and flexural behaviour of GFDST members. A total of 14 specimens are tested, including 8 stub columns, 4 beam-columns and 2 beams. For the axially compressed stub columns, the main test parameter is the hollow ratio of the cross section, and 2 corresponding hollow steel counterparts are designed to study the effect of the grout filling. For the beam-columns, the influences of load eccentricity are analyzed through test results. The failure modes, the strain distribution and the ductility of the GFDST members are studied in order to sufficiently evaluate the performance of the steel-grout composite member. The ultimate strengths of the GFDST members are estimated by the equations of concrete-filled double skin steel tubular members tentatively. It is found that all tested specimens failed in a ductile way, and the stiffness, the ultimate strength and the ductility of GFDST member is improved attributing to the in-filled grout. In addition, the predicted stiffness and strength results generally match well with the measured ones.