Prediction of ultimate load capacities of CFST columns with debonding by EPR: Fid-Bau Portal

Prediction of ultimate load capacities of CFST columns with debonding by EPR

Xue, Jun-Qing / Fiore, Alessandra / Liu, Zi-Hao / Briseghella, Bruno / Marano, Giuseppe Carlo

Abstract Concrete filled steel tubular (CFST) structures have become a viable alternative to reinforced concrete or steel structures due to several advantages. One of the most important is the confinement effect of the concrete core provided by the steel tube. However, this beneficial composite action will be probably weakened by debonding, so reliable formulations to predict the reduced ultimate resistance are needed. In this paper, a review of existing specifications and experimental tests carried out on compressed circular CFST columns with and without debonding, is given. Accordingly, more circular CFST long specimens with debonding should be necessary to understand the combined influence of slenderness ratio, load eccentricity ratio and confinement factor on the reduction coefficient ( $K_{D}$ ) of ultimate load capacities ( $N_{u}$ ). The combined influence of arc-length ratio and thickness of circumferential debonding gap on $K_{D}$ should be further studied by experimental tests. Moreover, the existing formulae for $K_{D}$ and $N_{u}$ show a low accuracy in predicting the test results and should be improved. To this aim, an evolutionary polynomial regression (EPR) MOGA-based methodology was performed to obtain more accurate formulations for $N_{u}$ and $K_{D}$ of circular CFST columns with debonding. The formulae extracted from the Pareto front of non-dominated solutions, demonstrate good accuracy, higher than the ones in literature. The proposed models are consistent with the physical interpretation of the studied phenomenon according to which $N_{u}$ and $K_{D}$ decrease as debonding parameters increase and can be used to calculate the real resistance of CFST structures.

Highlights • Experimental tests on compressed circular CFST columns with debonding are summarized. • The accuracies of existing models to predict the reduction coefficient K D of N u are low. • Formulaeto predict the ultimate load capacities N u with debonding are missing. • New formulaefor K D and N u are proposed by EPR. • The proposed models have good accuracies and physical meaning.