Effect of cross-section and stirrup configuration on the torsional performance of geopolymer concrete columns under compression

Abstract

To clarify the compression-torsion behavior of slag-based geopolymer concrete (GPC) columns with different cross-sections and stirrup details, quasi-static tests and finite element analyses were conducted on nine solid and three hollow-section columns. The test parameters were axial compression ratio, stirrup spacing, stirrup diameter, and cross-section configuration. The results showed that the specimens mainly failed in torsion-bending, shear-torsion, or compression-torsion modes, and a higher axial compression ratio promoted rapid propagation of diagonal cracks and intensified brittle failure. Hollow-section specimens showed faster stiffness degradation after cracking, and their peak torques were only 59.4%-71.4% of those of the corresponding solid specimens. Axial compression delayed cracking and enhanced torsional capacity up to an axial compression ratio of about 0.6; beyond this value, premature compression damage weakened the beneficial effect and promoted brittle post-peak degradation. The most favorable strength-deformation balance was obtained when the longitudinal bar-to-stirrup strength ratio was approximately 1.20. The finite element model reasonably reproduced the crack distribution and stress redistribution, but certain deviations remained in the curve slope and post-peak response. Current design models for ordinary concrete generally overestimated the torsional capacity of GPC columns, especially for hollow-section specimens. Based on these findings, a modified method applicable to C30 grade solid-section GPC columns was proposed, while the hollow-section tests provided preliminary evidence of the influence of section form on post-cracking torsional resistance. The mean ratio of predicted to experimental results was 1.014, indicating reasonable accuracy with a certain safety reserve.