Behavior of Partially Prestressed Beams Made with High Strength Fiber Reinforced Concrete


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Title: Behavior of Partially Prestressed Beams Made with High Strength Fiber Reinforced Concrete

Author(s): P. Balaguru and Ahmed Ezeldin

Publication: Special Publication

Volume: 105


Appears on pages(s): 419-436

Keywords: beams (supports); cracking (fracturing); deflection; fiber reinforced concretes; high-strength concretes; metal fibers; partial prestressing; prestressed concrete; shear strength; stresses; T-beams; Structural Research

Date: 12/1/1987

Results of an experimental investigation on the behavior of partially prestressed T-beams are presented. High-strength concrete with strengths higher than 8800 psi (60.6 MPa), mild steel with a yield strength of 60 ksi (413 MPa), 270 ksi (1,860 MPa) 7-wire strands, and 30-mm 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 two concentrated loads. The main variable was the fiber content that was varied from 0 to 250 lb/yd3 and (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 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 shear capacity reported in the literature. The fiber reinforced concrete beams undergo more deformation before failure. The increases in fiber content result 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.