Title: Shear Capacity of Prestressed Concrete Beams Using High-Strength Concrete
Author(s): Ashraf H. Elzanaty, Arthur H. Nilson, and Floyd 0. Slate
Publication: Journal Proceedings
Appears on pages(s): 359-368
Keywords: beams (supports); compressive strength; cracking (fracturing); di-agonal tension; high-strength concretes; prestressed concrete; shear strength;
pan-depth ratio; web reinforcement.
Results of an experimental investigation of the shear strength of prestressed concrete beams using concrete with compressive strength ranging to approximately 12,000 psi (83 MPa) are summarized. A total of 34 beams was tested, half designed for flexure-shear cracking and half for web-shear cracking. In each set, nine beams were without web reinforcement and eight had web reinforcement in the form of vertical stirrups. In addition to concrete strength, variables included longitudinal prestressed and nonprestressed steel ratios, shear span-to-depth ratio, amount of prestress force, and amount of web reinforcement. Test results are compared with strengths predicted using the equations of the 1983 ACI Building Code (ACI 318-83). The ACI Code approach is basically sound in considering two cases, web-shear cracking and flexure-shear cracking; both modes were observed and behavior in each was distinctly different. Present code equations for cracking load gave conservative results for all concrete strengths. For beams with stirrups, code equations for total shear strength were also conservative for all concrete strengths, but the degree of safety depended on several parameters, including concrete strength, that are not adequately considered by present equations.