The effect of slenderness ratio on modification of compressive strength of AISC code for composite columns (CFT) T-shaped with numerical (FEM) and experimental analysis

Abstract

Today, the use of CFT columns is increasing worldwide, due to the confinement of concrete and steel, speed of build, and no need of formwork, In these columns, the circular sections produce the most confinement effect for the core concrete That’s why these columns are mostly made in circular and square shapes. But sometimes other geometrical shapes such as (T) are used, which provide less confinement for core concrete than circular and square sections. The AISC Code for the Calculation of compressive strength (Pn), considers the capacity reduction factor of concrete (C2) only for circular and square sections. The Code provided the value of this coefficient for circular sections due to greater confinement in core concrete 0.95 and square sections 0.85 but did not provide a coefficient for (T) shape. So in this study, 12 specimens in three groups of experimental, numerical and theoretical were used to calculate the reduction coefficient of concrete strength (C2) and to investigate the effect of slenderness ratio on this coefficient. Finally, it was found that the reduction coefficient of concrete (C2) for (T) shape due to lower confinement of core concrete was on average 31.69% less than a circular section and 23.13% less than square section. Also with a 64% increase in slenderness ratio, the reduction coefficient of concrete strength (C2) decreased by 14.82%.