Time-dependent behaviour of expansive concrete-filled steel tubular columns

Expansive concrete-filled steel tubes (ECFST) are commonly used in modern building and bridge applications. Despite their popularity, limited attention has been devoted to investigate the time-dependent behaviour of such elements. This paper intends to provide new experimental data for the benchmarking of numerical models. Particular attention is devoted to ECFST elements first loaded at quite early concrete ages, e.g. 5 days after concrete casting, to reflect the construction site practice. Eleven ECFST short columns were subjected to different levels of sustained axial loads applied at different concrete ages. Seven columns were then tested to failure to evaluate the long-term effects on their ultimate capacity. The accuracy of four currently available concrete models, EC2, MC90, AFREM and B3, in predicting the long-term response of ECFST elements was investigated based on the related experimental results. Investigation shows that the assumption of linear creep can apply to ECFST elements with initial concrete compressive stresses up to approximately 80% of the concrete strength, rather than the normally accepted upper limit of 40%50%. During the service life, confinement does not affect the performance of ECFST elements. Model EC2 is adequate to predict the time-dependent response of ECFST elements.