Compressive behaviour and design of L-shaped columns fabricated using concrete-filled steel tubes

The behaviour of unusual composite column sections is difficult to examine owing to their asymmetric geometry. In this study, seven L-shaped columns fabricated using concrete-filled steel tubes connected via double-vertical steel plates (LCFST-D columns) were tested under axial compression. The failure modes, load-deformation relationship, strain distribution, ductility, and strength index of the columns were studied. Test results demonstrated that the local buckling of the vertical steel plates was delayed by filling with concrete. The bearing capacity and ductility ratio increased by 21.1% and 8.1%, respectively, compared with the specimen without concrete in the vertical steel plates. Transverse stiffeners were used to increase the axial stiffness by restraining the deformation of the vertical steel plates. However, the effect of the transverse stiffeners on the bearing capacity was negligible. The behaviour of the LCFST-D columns with concrete filled in between the two vertical steel plates, without the transverse stiffeners, was more favorable than the LCFST-D columns with the transverse stiffeners, and thus recommended for practical engineering application. The mono-columns worked more cooperatively in this connecting pattern. 3D nonlinear finite element models were developed and verified to analyze the mechanical properties and bearing capacity of the LCFST-D columns. The approach is verified by the experimental results and the available current design codes to be reasonably conservative. EC4 showed the best agreement with the experimental values. The results of this study provide a basis for the application of LCFST-D columns in high-rise composite structures.