Nonlinear concrete model for an internally confined hollow reinforced concrete column

A hollow reinforced concrete (RC) column has been used to obtain a more economical design by reduction of the material or the self weight of the column. Although a hollow RC column offers a high effectiveness of section properties, it may show poor ductility owing to brittle failure at its inner face. In order to develop a more economical and safer model for a RC column, an internally confined hollow (ICH) RC column and its non-linear concrete model were proposed with the considerations of confining effects. To determine the relation of stress-strain for the concrete in an ICH RC column, possible failure modes of the column were investigated and the confining pressure was derived from equilibriums for each failure mode. A computer program was developed with respect to the derived equilibrium equations and parametric studies were performed to evaluate the application of the developed program. The ICH RC column significantly improved its strength and ductility by the internal confinement.