Although the influence of flexural stiffness of perimeter ties on the confining pressure has been investigated by experiments [Sun et al. (1996)and Sato and Yamaguchi (2000)], very few researchers studied this problem analytically. Assa et al. (2001a and 2001b) proposed analytical models based the expansion of concrete core and the transverse deformation of perimeter ties for determining the confining pressure at peak strength for circular RC columns Furthermore, for RC tied columns, the nonuniform confinement pressure along the height of the column is transformed to an equivalent uniform confining stress provided by an equivalent circular envelope, using the strain energy concept.