Equation for Computing Ultimate Flexural Strength of Circularly Retrofitted Concrete Columns

A simplified design equation was proposed in this paper to evaluate ultimate flexural strength of reinforced concrete columns retrofitted by circular steel tube. Ultimate axial load versus moment interactive curve of a circularly retrofitted column section, which is defined by the proposed design equation, consists of two parabolas. The proposed design equation has a very simple mathematical expression and enables structural engineer to easily take into account confinement effect of circular steel tube on ultimate flexural strength of the retrofitted column.