Side-Face Reinforcement for Flexural and Diagonal Cracking in Large Concrete Beams

Abstract

The current American Concrete Institute (ACI) Building Code and American Association of State Highway and Transportation Officials (AASHTO) Bridge Code requirements for side-face reinforcement are meant to control flexural cracking in the webs of large concrete beams and may not provide adequate diagonal crack control for certain exposure conditions. Twenty-one large concrete beam elements with 1,200-mm deep webs were tested in a specially constructed apparatus to study the influence of amount and arrangement of side-face reinforcement in controlling both flexural and diagonal cracking in large concrete beams. The amount of side-face reinforcement was varied from 50% to 300% of what is required by the current ACI Building Code and AASHTO Bridge Code. Deformed reinforcing bars, welded wire fabric, and hooked steel fiber were included in the study. Over 11,000 crack widths were measured with a microscope on the 21 specimens, and an analysis of the crack data revealed the relationship between crack width and average strain and the ratio of maximum to average crack widths. A procedure is presented for estimating diagonal crack widths in the webs of large beams caused by service level shear stresses, and a general design procedure is presented for the amount of side-face reinforcement needed to control both flexural and diagonal cracking in the webs of large concrete beams. The required spacing of side-face longitudinal reinforcing bars depends on the maximum acceptable crack width, strain of the longitudinal reinforcement on the flexural tension side, magnitude of the applied shear stress, amount of transverse reinforcement, and the diameter of and cover to the side-face reinforcing bars. A design example illustrates the proposal.