Optimum confining effect in steel composite hollow RC column with inner tube under compressive load

An internally confined hollow reinforced concrete (ICH RC) column offers strong and durable confinement by the reinforcement of the inner tube. When the concrete in an ICH RC column experiences axial pressure, an inward radial pressure is produced by the arching action. This radial pressure is resisted by the concrete and the inner tube. Previous research considered the outer pressure and inner pressure to be equal. However, the inner pressure acting on the inner tube is lower because it is partially resisted by the concrete. Therefore, to determine the optimum confining effect on the concrete by the confining condition, it was necessary to determine reasonable values for the inward and outward confining stress in ICH RC columns. In the current study, the confining effects of concrete in an ICH RC column were investigated and evaluated using finite-element (FE) analysis. Parametric studies were performed to determine the factors affecting the confinement of the core concrete in an ICH RC column. The hollow ratio was found to be the main factor affecting the internal confining stress in an ICH RC column. Using the results of FE analysis, estimation equations for the internal confining stress and a new modified equation for the failure condition were developed.