ABSTRACT
Equations 1 and 2 imply that, for the same D, ffrp, and tfrp; fl , is larger on the hollow core columns because of the hollowpart. However, for solid columns fl results in a triaxial stress state on any concrete element within the column whereas this confinement creates only a biaxial state of stress on a concrete element within a hollow column resulting in less capacity increase (Zahn et al. 1990; Yazici & Hadi 2008).
