Shear and Flexure Analysis of Prestressed Concrete T-Beams containing Steel Fibers over Partial or Full Depth

Twenty-three partially prestressed steel fiber reinforced concrete T-beams have been tested to investigate the shear and flexure capacity, and the resulting mode of failure. These beams have been cast using three grades of concrete (35 MPa, 65 MPa and 85 MPa) with fibers (Vf = 1,5 percent) in different locations in the cross section of the beam (web, flange or full depth). The beams designed for flexural failure were provided with a transverse steel reinforcement ratio of 0,66 percent while those designed to fail in shear had 0,33 percent of transverse steel. These beams have been tested varying the shear span to depth (a/d) ratio between 1,59 and 5,30. Based on the test results, prediction models were developed to compute flexural and shear capacities of the partially prestressed steel fiber reinforced beams. The proposed model accounts for the contribution of fiber pullout to sustain the opening up of cracks in beam. Addition of steel fibers in partial or full depth in partially prestressed concrete beams transforming its mode of failure from brittle shear to ductile flexure has been analytically investigated. The plots of the variation of the ultimate moment carrying capacity (Mu) against the shear span to depth (a/d) ratio indicate the transition of failure mode from arch to beam action or shear to flexure occurs at lower values of 'a/d' when fibers are introduced into the matrix with respect to the plain concrete beam. The transformation of failure mode takes place for lower value of 'a/d' ratio for high strength concrete beams than for normal strength concrete beams.