Confinement effectiveness in circular concrete columns

This paper presents an analytical study of the confinement effectiveness in circular concrete columns confined by transverse reinforcement. The analytical derivation includes several stages. The first stage includes the solution to the passive confinement problem of a linear elastic cylinder, confined by a sequence of equally spaced lateral rings under axial stress. The derivation is based on and preceded by a solution to the problem of active confinement. Next, based on the solution to the passive problem, an equivalent lateral pressure is derived by replacing the steel ties with a uniform equivalent tube of constant thickness. The equivalent tube thickness is employed in this paper to analytically determine the confinement effectiveness of the problem’s variables, such as the ties spacing and cross-sectional area or the concrete–steel moduli ratio. The results are also examined and compared with the widely used empirical arch method. The comparison shows that within the practical range of the RC variables the current analytical model is in very good agreement with the empirically developed model.