Hysteretic behavior of geopolymeric recycled concrete-filled steel tubes under combined compression-bending-torsion

The hysteretic behavior of 16 geopolymeric recycled concrete-filled steel tubes (GRCFST) under combined compression-bending-torsion was experimentally investigated. The effects of key parameters such as (i) the recycled aggregate content, (ii) the slag content, and (iii) the moment-torsion ratio were compared and discussed. The test results showed that the structural behavior of GRCFST was very similar to that of ordinary CFST in terms of strength, stiffness, ductility, and energy dissipation. Both GRCFST and ordinary CFST experienced more flexural failure characteristics when the moment-torsion ratio was increased, whilst they experienced more torsion failure characteristics when the moment-torsion ratio was decreased. Numerical models were established to benchmark test results and perform parametric studies. Revised design formulae were proposed to consider the effect of slag content and recycled aggregate replacement ratio. The applicability of the proposed formulae in predicting the strength of GRCFST under combined compression-bending-torsion was evaluated.