Design Issues about the Bar Lay-Out at the Dapped Ends of Simply-Supported One-Way R/C Slabs

Directly- or indirectly-supported R/C slabs are frequently used in the covers of small-tomedium underground facilities, where the service loads are often rather limited, but very severe loads cannot be ruled out in accidental situations. To have fresh information on the structural performance and cracking of R/C slabs simply supported along their short sides via corbels (dapped ends), four rectangular slabs subjected to transversely distributed or concentrated loads have been recently tested in Milan (b x L = 1.30 x 2.20 m; simply-supported span = 2.10 m; thickness = 15 cm). The load was applied either at midspan (in the bending tests, not presented in this paper), or at 1/10 of the span (in the shear tests). Two bar arrangements were investigated with straight or bent-up bars in the main body, and straight bars or hooks in the corbels. In the D zones of the slabs tested in shear, the concentrated load induces a rather complex 3-D crack pattern, with a limited reduction in the bearing capacity, compared with the cross-wise distributed load. Rather simple strut-and-tie models applied to the slabs with bent-up bars and hooks, and the equations provided by European and North-American codes for the beams devoid of transverse reinforcement are shown to yield realistic predictions for the bearing capacity at the ultimate limit state. In the former case, however, modelling the bond along the tension reinforcement of the corbel requires some care, because of bond local and global effects. Last but not least, refining bar layout confirms - once more - that slab performance can be markedly improved with little extra effort.