Size Effect on Nominal Strength of Lightweight and Normal Concrete-Filled Steel Tube Columns under Axial Compression: Mesoscale Simulations

With the devolvement of large-span structures and super high-rise buildings, lightweight aggregate concrete (LWAC) materials have been widely utilized. The main content of this work is to explore the failure and size effect of lightweight aggregate concrete-filled steel tube (LWACFST) columns under uniaxial compression. A three-dimesnional mesoscale simulation approach considering concrete heterogeneity was developed, in which the ideal bond was assumed between the steel tube and inner concretes. The failure of geometrically similar square and circular LWACFST/CFST columns under axial compression having different structural sizes and transverse constraints was modeled and explored. The size effect on the nominal compressive strength of the columns was examined. The influences of aggregate type, column cross-sectional type, and constraint effect generated by the steel tube on the size effect in axial compressive failure are also investigated. The results indicate that an obvious size effect in axial-compressive failure can be found for both LWACFST and CFST columns. With the increase of the confinement degree of steel tube, the size effect on nominal compressive strength would be weakened. The LWACFST columns exhibits a more obvious size effect than the CFST columns. Moreover, the size effect on the compressive strength of the circular columns is obviously weaker than the effect on square columns. Finally, considering the quantitative influence of confinement coefficient, a novel size effect law (SEL) for quantitatively describing the size effect in axial-loaded CFST columns was proposed. The accuracy and reasonability of the proposed SEL was verified by the available test data.