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Title: Shear Capacity of Longitudinally Reinforced Beams--A Fracture Mechanics Approach

Author(s): K. O. So and B. L. Karihaloo

Publication: Structural Journal

Volume: 90

Issue: 6

Appears on pages(s): 591-600

Keywords: beams (supports); bond stress; shear properties; span-depth ratio; Design

DOI: 10.14359/4489

Date: 11/1/1993

Abstract:
The conventional strength theory has been used for a century to study the shear behavior of longitudinally reinforced beams, but it still cannot explain the size effect and the catastrophic mechanism associated with diagonal shear failure. Several attempts were made in the last decade using fracture mechanics. Among these were Jenq and Shah, who suggested that the ultimate shear resistance could be calculated by adding the contributions from the tension-softening effect of cracked concrete and the bond of reinforcement. A power law was assumed to represent the distribution of steel force along the bar axis. This model was reviewed by Karihaloo, who found that the exponent N of the power law would be underestimated if dowel action and aggregate interlock were ignored. In this paper, two methods are suggested to estimate the maximum steel force and, hence, the contribution from steel by studying the ultimate bond stress of a reinforcing bar and the longitudinal splitting failure of concrete due to bond stress. It is observed that both methods give consistent results, and the method based on the analysis of the splitting failure of concrete is insensitive to the shape of the tension-softening diagram of concrete. When the contributions from dowel action and aggregate interlock are estimated and included, the shear capacity of the beams can be better predicted. The predictive capabilities of the improved fracture mechanics approach proposed here are confirmed by test results.


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