Behaviour of steel-fibre-reinforced geopolymer concrete-filled square steel tubular stub column under axial compression

Resource utilisation of industrial waste has become a crucial issue in construction aiming for sustainable development. Research on geopolymer concrete-filled square steel tubular (GCFST) structures is limited. Moreover, methods for calculating the bearing capacity of steel-fibre-reinforced GCFST (SFRGCFST) structures require further investigation. This study presents an experimental and analytical investigation of the axial compression performance of SFRGCFST stub columns. Twenty-four specimens were tested to assess the effect of steel tube thickness, steel fibre (SF) volume fraction, SF aspect ratio, and concrete strength grade on failure modes, load-deformation behaviour, load-strain response, ultimate resistance, and ductility of SFRGCFST columns. The results indicated that the failure modes of SFRGCFST columns are influenced by the coefficient index, which varies with the test parameters. When the coefficient index exceeded 0.88, the failure mode of the specimens transitioned from shearing failure to waist-drum-shaped failure. The average ultimate bearing capacity of the SFRGCFST columns increased by 35.13% compared with that of the plain concrete-filled steel tubes (CFSTs). When the SF volume fraction reached 0.9 %, the ultimate bearing capacity of the SFRGCFST columns increased by 21.85 % compared with that of steel-fibre-reinforced concrete-filled steel tube (SFRCFST) columns. The incorporation of SF significantly improved the deformation capacity and ductility of the SFRGCFST columns and moderated the slope of the post-peak load-displacement and load-strain curves, slowing the descent of the curve. Utilising the multi-axial strength criterion and mechanical equilibrium equation for square CFSTs, a formula for calculating the ultimate bearing capacity of SFRGCFST stub columns was developed. This formula enables accurate prediction of the axial compressive load capacity of SFRGCFST stub columns and provides a basis for revising relevant standards.