Applications of bent-up bars as shear and integrity reinforcement in R/C slabs

Bent-up bars were extensively used as shear reinforcement in beams and slabs from the first R/C developments up to the 1970’s. Their use was justified by the fact that they allowed enhanced development of the tensile reinforcement at the same time they acted as shear reinforcement. New reinforcing bars (with reduced development lengths) in combination with shear reinforcing systems led however to the abandon on their use. Recently, interest has again grown on the use of bent-up bars in flat slabs. This is explained by their efficiency both as shear reinforcement (alone or in combination with stirrups) and as integrity reinforcement. In this paper, the results of 7 full-scale specimens (3.0×3.0×0.25 m) reproducing the support region of an actual flat slab with different layout of bent-up bars are presented. The tests show different potential failure modes and allow understanding the contribution of this reinforcement to the shear-carrying capacity of the specimens. Additionally, the performance of bent-up bars as integrity reinforcement is discussed with reference to 9 half-scale specimens (1.5×1.5×0.125 m) where the influence of the development conditions of the bent-up bars is clearly assessed.