Uniaxial Interaction Chart Of Reinforced Concrete Column Confined By Transverse Reinforcement

Abstract

Transverse reinforcements have been used in reinforced concrete columns due to their advantages to fix in position of longitudinal reinforcement during construction, to shorten the buckling length of the reinforcement, to prevent shear failure and to confine the concrete. However transverse steels have confinement advantage, the design of reinforced concrete column is based on the simplified stress- strain model of unconfined concrete, and does not account for the strength gain due to confinement. The existing column design charts are also prepared based on the unconfined concrete and do not consider the strength enhancement; consequently they are in conservative side and gives uneconomical longitudinal reinforcement. This research is conducted, analytically to determine the effect of confinement on reinforced concrete column capacity in terms of the column axial force- bending moment interaction diagram. The confined stress-strain model given in Eurocode-2 for normal strength concrete was used. The lateral pressure for circular and rectangular column section was determined for selected transverse reinforcement configurations, which are usually used for uniaxial bending. The interaction diagrams were drawn using non-dimensional axial force and bending moment capacities, which are computed at different neutral axis depths using C++ programing language. The study shows that confinement increases the strength and ductility of the concrete, which results a considerable enlargement of axial force -bending moment capacity in the compression controlled region of the interaction diagram. Using additional cross and overlapping ties as lateral reinforcement in reinforced concrete column, further increases the column axial force- bending moment capacity. It is found that, confinement is more effective in circular sections than rectangular sections. Numerical calculation for comparison also made and it shows that reinforced concrete column designed by considering confinement requires lesser amount of longitudinal reinforcement than a column designed with the existing column design chart. Finally Uniaxial design charts for circular and rectangular reinforced concrete columns with different transverse reinforcement configurations are prepared and can be applicable for design