Behaviour of confined over-reinforced self-compacting concrete beams

R. Kumar, Indian Institute of Technology Roorkee, India 
B. Singh, Indian Institute of Technology Roorkee, India 
P. Bhargava, Indian Institute of Technology Roorkee, India 


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.