Post-creep buckling load resistance of recycled aggregate concrete-filled steel tubes: Numerical modelling and calculation method

Recycled aggregate concrete-filled steel tubes (RACFST) can enhance the performance of recycled aggregate concrete through the confinement effect, promoting its structural applications. Although extensive researches have shown that RACFST members exhibit comparable capacities to those of traditional concrete-filled steel tube (CFST) members under ultimate conditions, the inclusion of recycled aggregate remarkably increases the long-term deformation of RACFST members, increasing the pre-buckling deformation and thus decreasing the post-creep buckling load resistance. To date, this influence has not been well quantified, and no prediction method is available. To address this gap, a finite element model (FEM) was developed to analyze the post-creep buckling behavior of RACFST. Based on comprehensive parametric analysis, reduction factors were proposed to account for the creep history influence on the short-term load resistance of RACFST. The reduction factors were proposed in two forms to serve for the two kinds of stability design formulas for CFST that are commonly used in current standards, i.e., (1) Perry's formula, and (2) the regressed formula. For Perry's formula, the reduction factor was derived theoretically based on Perry's rule; For the regressed formula, the reduction factor was proposed based on regression analysis using the FEM results. Validation results indicate that both the theoretical and regression formulas can provide good accuracy, with a maximum deviation of ± 5 % compared to the FEM results.