Effect of Moderate Confinement on Flexure Behavior Of Reinforced Concrete Beams

Abstract

It is well known that confined concrete has better stress- strain behavior in compression than unconfined concrete. This concept has traditionally been applied to columns where compression concrete is confined through better arrangement of longitudinal as well as lateral steel for improved strength and ductility. On the other hand, failure of compression concrete in reinforced concrete beams is avoided, being brittle in nature, by imposing restriction on amount of longitudinal reinforcement so that the failure should be governed by yielding of steel for ductility requirements. The design of over-reinforced concrete beams is therefore, not permitted by codes of practice. The research on confinement of compression concrete in beams has already been initiated to explore the possibility of improved behavior in terms of strength and ductility. Ten reinforced concrete beams were tested, which included four traditionally designed beams and six confined beams. Flexural span of confined beams was provided with steel stirrups extending to half beam depth for confinement. Both over-reinforced and under-reinforced beams were tested. Experimental results indicated that ductility of confined beam is improved with the confinement especially in over-reinforced beams. The result also lead to the requirement of revision in maximum allowable longitudinal reinforcement in codes if adequate confinement stirrups are provided.