Size Effect on The Shear Strength of Reinforced Concrete Beams

Abstract

Given the great discord concerning the mechanisms that govern shear failure, the shear behaviour of concrete bearn elements with no transverse reinforcement is investigated. The variables introduced in the experimental program are member depth, amount of longitudinal steel reinforcement and concrete strength. The effects of these variables on the shear stress at failure of the concrete are investigated. Two geometrically similar series of beams of different concrete strengths are compared. Beam heights in each of the series range from 90 mm to 960 mm and al1 the beams have a constant a/d ratio of 2.5. Results show a strong "size-effect" in the behaviour of concrete beam or one-way slab elements subjected to shear, where deeper members have smaller shear stresses at failure than shallower ones. Increasing the amount of flexural reinforcement increases the shear stress at failure while increasing the concrete compressive strength has little or no effect on the diagonal shear resistance of concrete. The AC1 Code equations for shear are found to be unconsewative for large elements while the CSA Standard simplified shear design method yields conservative predictions within the range of bearns tested. For the beams tested. with an a/d ratio of 2S1 the combination of the modified compression field theory and a strut-and-tie analysis provides more accurate predictions.