Size effect of square concrete-filled steel tubular columns subjected to lateral shear and axial compression: Modelling and formulation

Abstract

Concrete-filled steel tubular (CFST) short columns under the action of wind and seismic load often endure high shearing force and show brittle shear failure, which may exhibit obvious size effect. In this study, a three-dimensional meso-scale simulation method that can consider both the concrete heterogeneity and the contact behavior between concrete core and steel tube was established to investigate the failure behavior and size effect of square CFST columns under combined lateral and axial loads. After verification of the meso-scale model, simulation tests were carried out to discuss the influence of shear-span ratio, axial compression ratio and steel ratio on the failure modes, the nominal shear strength, the ductility and the size effect of square CFST columns. Results indicate that, when the shear-span ratio increases from 1.0 to 3.0, the failure mode of CFST columns turns from brittle shear failure to ductile bending failure, the nominal shear strength decreases and ductility increases, and the size effect in shear would be weakened. The nominal shear strength increases and the column shows better ductility with the increasing axial compression ratio less than 0.4, while the nominal shear strength decreases and the columns present obvious brittleness with the increase of axial load larger than 0.4. Moreover, as steel ratio increases from 0.05 to 0.15, the nominal shear strength and ductility of CFST columns increase, and the size effect on nominal shear strength cannot be weakened. At last, a theoretical formula that can quantitatively show the influence of shear-span ratio on size effect in shear strength was proposed to predict the shear capacity of square CFST columns. The available test data and the simulation results illustrate the rationality and applicability of the theoretical formula.