Innovative compressive design resistance and behaviour of concrete-filled short columns with stiffened square steel sections

Abstract

The concrete-filled tubular steel columns with stiffened steel sections, abbreviated as CFSST, have lower sensitivity to local buckling and higher confinement of the concrete core than standard concrete-filled tubes. Herein, available test results for CFSST short columns with a single stiffener or multiple stiffeners are collected from the literature. They are analysed and then a new power law formula for the lateral confining pressure (frp) is proposed. After that, the results provided by the formula are verified by simulating the behaviour of the available test specimens using ABAQUS finite element (FE) software. The results of the test and FE analyses reveal that the proposed frp formula performs well and it is used further in the parametric studies on the strength and behaviour of CFSST columns, namely the effect of (i) the plate slenderness ratio, (ii) the steel yield strength, (iii) the concrete cylindrical strength and (iv) the number of stiffeners and their depth. Increasing the concrete cylindrical strength is found to provide the largest increase in the strength of the columns compared to other parameters, although it reduces the ductility of the columns. In addition, the resistance values for the CFSST columns are calculated on the basis of Japanese, British, European and Chinese structural standards for comparison with the values obtained numerically. Because these standards provide conservative predictions, an innovative design formula is suggested for CFSST columns based on the analytical expression developed for the lateral confining pressure. The new design formula yields much better predictions than the formulae in the existing structural standards.