Behaviour of confined over-reinforced self-compacting concrete beams

Abstract

In many structural applications it is desirable to use a high percentage of steel reinforcement in beams to minimise structural depth while still providing adequate stiffness. This investigation demonstrates that by confining the compression zone of an over-reinforced beam with a steel helix, considerable strength, stiffness and ductility can be achieved, even with a tension steel content as high as 4·79%. This is possible because the helically confined compression concrete becomes triaxially stressed during loading, leading to a high uniaxial strain capacity at an enhanced stress level. Self-compacting concrete has been used to ensure effective concreting of the over-reinforced beams. The proposed analytical approach based on the moment–curvature characteristics of the over-reinforced section gives a reasonably accurate prediction of the load-displacement behaviour of the over-reinforced beams. The serviceability limit states of cracking and deflection have been examined and the quality of the hardened self-compacting concrete in the beams has been found to be satisfactory from ultrasonic pulse velocity measurements.