Axial compressive behavior of geopolymer recycled brick aggregate concrete-filled steel tubular slender columns

Geopolymer and recycled brick aggregates are applied into the concrete-filled steel tubular column to provide a promising solution to environmental sustainability. This paper investigates the mechanical behavior of geo-polymer recycled brick aggregate concrete-filled steel tubular (GRBAC-FST) slender columns under axial compression. Apart from cross-section type, the replacement ratio of brick aggregates (BA) and slenderness ratio are also selected as the main variables. The analysis of the failure mode, bearing capacity, deformation behavior, and strain behavior is conducted. A modified stress-strain model for the GRBAC-FST slender column is proposed and validated, then the parametric analysis on phi-lambda relation curves is performed to propose a simplified calcu-lation method for the bearing capacity. Results demonstrate that GRBAC-FST slender columns exhibit obvious lateral deflection, and mid-span bulging of steel tube. Compared with square specimens, circular specimens exhibit plane fracture of concrete, and developed higher bearing capacity and better plastic deformation ca-pacity. The ultimate strength of GRBAC-FST slender columns decreases with the increase of the replacement ratio of BA and slenderness ratio. The stability coefficient phi decreases with the increase of the slenderness ratio, the yield strength of the steel tube and the concrete strength, while it was little affected by the steel ratio. The modified stress-strain model could well reflect the full-range response of GRBAC-FST slender columns under axial loading. The proposed calculation method could be used for the compressive bearing capacity of GRBACFST slender columns, with satisfying accuracy and efficiency.