Behavior of partially prestressed beams made with high strength fiber reinforced concrete

This paper presents the results of an experimental investigation on the behavior of Partially Prestressed T Reams. High strength concrete with strengths higher than R,ROO psi (60.6 MPa), mild steel with a yield strength of 60 ksi (413 MPa), 270 ksi (1,860 MPa) 7 wire strands and. 30mm fibers with hooked ends were used for the entire investigation. Condensed silica fume and high range water reducing admixture were used to obtain the high strength concrete. Six T beams were tested using a simply supported span of 7 ft. 6 in. (2286 mm) and 2 concentrated loads. The main variable was the fiber content which was varied from 0 to 250 1b/yd³ (147.5 kg/m³). Only the minimum shear reinforcement (stirrups) was provided for all the beams. The flexural reinforcement was designed to create a shear failure, in order to evaluate the fiber contribution to shear at low shear spans. The beams were instrumented to measure stresses in nonprestressed and prestressed reinforcement, curvature, crack spacing, crack width, and deflection. Companion cylinders were tested to obtain the compressive strength of concrete. Five out of six beams failed in shear mode. The fibers do contribute to the shear capacity. However, the contribution of fibers to shear is less for low shear spans as compared to the contribution of fibers to !!hear capacity reported in the literature. The fiber reinforced concrete beams undergo more deformation before failure. The increases in fiber content results in consistent increase in flexural stiffness and cracking moment, decrease in crack spacing and maximum crack width, and reduction in reinforcement stresses and concrete strains.