Shear failures in cantilevered reinforced concrete slab-strips without transverse reinforcement

Abstract

Design of slabs without shear reinforcement is, in practice, based mainly on empirical codified methods, derived on the basis of a large number of tests. However, the vast majority of these tests involves simply supported beams, with substantial amounts of longitudinal reinforcement, subjected to three- or four point bending. This paper presents the results of a significant experimental programme comprising eighteen simply supported – cantilevered slab strips without stirrup reinforcement, and with a light amount of longitudinal reinforcement. Stirrups in the surrounding parts founded a shear critical region located in the hogging region of the simple span. All beams failed in shear within this shear critical region, the slenderness of which was fixed for all the beams. The influence of the concrete strength, which is of special interest in relation to lightly reinforced members, was investigated by varying the concrete strength systematically within the test series. The influence of the concrete strength and mix with respect to crack roughness was further studied using a large number of concrete cores prepared with coloured epoxy. The cores were all extracted from various zones containing critical and “non-critical” shear cracks. Photogrammetric measurements (digital image correlation) and optical fiber measurements were conducted in the shear critical region on all tested specimens, and detailed analysis on the propagation and kinematics of critical cracks are presented.