Experimental Investigation on Hybrid Fibre-Reinforced Concrete Deep Beams

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S. K. Kulkarni , Dr. S. A. Halkude


Researchers have established that the inclusion of steel fibres in concrete for R.C. deep beam delays crack formation, transforms the brittle behaviour of deep beams into increasingly ductile behaviour, prevents sudden shear failure and improves the shear strength of deep beam. It is also recognized that using hybrid fibre reinforced concrete (HFRC),  reinforced with two or more different types of fibres, can produce better results. The hybrid fibre combination of metallic and synthetic fibres provides effective confinement and better bonding with concrete, as well as it allows for easier stress transfer from matrix to fibres. In this connection, the present study focuses on the inclusion of hooked end steel fibres and fibrillated polypropylene fibres in predefined proportions in the concrete mix to cast HFRC deep beams and study the effects. The present experimental investigation demonstrates that the inclusion of hybrid fibres improves the strength properties of concrete significantly. Moreover, it leads to a rise in first crack load, a significant increase in ultimate shear strength, and a substantial increase in reserve strength of HFRC deep beams when compared to conventional R.C. deep beams. Also, study reveals that it is possible to replace conventional shear reinforcement in deep beams with 1 per cent hooked end steel fibres and 0.3 per cent fibrillated polypropylene fibres by volume of concrete, to obtain high shear strength deep beams with increased ductility, reserve strength and lower reinforcement congestion.

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