Experimental Behavior of Hybrid Steel and Polypropylene Fiber Reinforced Concrete Deep Beam Containing Openings

Abstract

Twelve simple span reinforced concrete deep beams were tested under symmetrically two points top load to examine the effect of steel fiber and polypropylene fiber and influence of the transverse circular openings on their behavior. The variables investigated involve beams with and without openings, the volume fraction of fibers, shear span to effective ratio a/d, and inclined reinforcement around the openings. All the beams had the same overall dimensions, flexural reinforcement and opening size. Many mixes have been used by combination between steel fibers and polypropylene fibers with different percentages of (1%SF-0%PPF), (0.75%SF-0.25%PPF), (0.5%SF-0.5%PPF), (0.25%SF-0.75%PPF), (0%SF-1%PPF) in addition to mix without fibers. The test results showed that fibers greatly increase the diagonal cracking strength and shear strength of reinforced concrete deep beams, where the variation of the type of concrete from normal concrete to hybrid concrete for deep beam contains openings led to increase the ultimate strength by about 30%. In addition, it was found that the shear capacity of deep beams increased when the shear-span/effective depth ratio decreased. The inclined reinforcement around the opening was observed to be very efficient in improving the ultimate load capacity and deflection response.