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 modifies this formula, and proposes the formula considering the effect of web reinforcements on the shear capacity of concrete. The proposed formula takes into account the fact that the presence of web reinforcements has a strengthening effect on the shear capacity of concrete and reduces the effect of the shear span on the nominal stress. Comparison with existing test results involving 91 tests indicates that, compared to the formula in the current building codes, the coefficient of variation of deviations from the formula is reduced to less than one.
The results confirm that the size effect on the concrete shear strength still exists in the presence of web reinforcements but it is milder than without web reinforcements.
