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 stressstrain 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.

The confining transverse reinforcement has been arranged in plastic hinge region to resist the lateral load, increasing the lateral confining effect in the substructure of the bridge. Columns increased the seismic performance by securing the stiffness and ductility. The calculation method of confining transverse reinforcements is reported in AASHTO-LRFD specification. This specification is only proposed for solid RC columns. In this reason, if this specification is applied to another column as composite column besides solid RC columns, a proper evaluation of the column cannot be done. In particular, composite hollow RC columns have limits for applying this specification. The composite hollow RC column consists of transverse longitudinal reinforcement, cover concrete, core concrete, and an inner tube inserted on hollow face. It increases the ductility, strength, and stiffness of the composite hollow RC column. This paper suggests a modified equation for an economical and rational design through an investigation of displacement ductility when applied to the existing specifications of the composite hollow RC column. Moreover, parametric study is performed for evaluating the detail behavior. Using these results, a calculation method of economic transverse reinforcements is proposed.