Eccentric Compression Behavior of Geopolymer Concrete-Filled Stainless Steel and Carbon Steel Tube Stub Columns

Abstract

This paper presents an experimental investigation of the structural performance of circular geopolymer concrete-filled stainless steel and carbon steel tube stub columns subjected to combined compression and bending. A total of eight stub columns were tested under eccentric compression, consisting of four geopolymer concrete-filled stainless steel (GCFSST) specimens and four geopolymer concrete-filled carbon steel tube (GCFST) specimens. The main test variables were the steel tube material, the eccentricity ratio (e/D = 0.4), and the diameter-to-thickness ratio (D/t = 25.82–51.13). The geopolymer concrete was produced using fly ash and rice husk ash with an RHA:FA ratio of 60:40 by weight and cured under the ambient condition. The effects of the test variables on failure mode, load–deformation response, ultimate strength, stiffness, ductility, and strain development were investigated. The results showed that the stainless steel tube specimens achieved 21.3–41.8% higher peak loads and 25.8–53.8% higher moment capacities than the corresponding carbon steel tube specimens, while also exhibiting more gradual post-peak load degradation. In addition, the D/t ratio significantly influenced the initial stiffness, local buckling behavior, and ultimate strength. Finally, the applicability of Eurocode 4 (EC4) and AISC 360-22 design provisions for predicting the strength of GCFSST and GCFST stub columns under combined compression and bending was evaluated. Using a simplified treatment of stainless steel strain hardening and geopolymer concrete confinement behavior, both provisions provided conservative predictions.