Size Effect in Diagonal Shear Failure: Influence of Aggregate Size and Stirrups

Fracture mechanics of brittle failures of concrete structures due to the propagation of a cracking zone indicates that the nominal stress at failure should not be constant but should decrease as the structure size increases. This size effect may be described by a simple size-effect law recently derived by dimensional analysis and similitude arguments. A formula for diagonal shear failure based on this size-effect law was published, verified, and calibrated by a large set of data from the literature. The present paper improves this previous formula in two respects: fJ) the effect of maximum aggregate size, distinct from the effect of the relative beam size, is incorporated and (2) the formula is extended to cover the effect of stirrups on the shear capacity of concrete. The new formula is verified and calibrated according to a larger data set than before, consisting of several hundred test results compiled from the literature. [t is shown that the new formula achieves an appreciable reduction in the coefficient of variation of the deviations of the measured data from the prediction formula.

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