Indirectly-supported one-way R/C slabs: Durability and safety issues

Simply-supported one-way R/C slabs are commonly used in the covers of small and medium underground facilities, where durability is the main issue face with rather limited service loads and short spans (2-4 m [6.5-13.0 ft]). The structural performance, however, should not be underrated, as being the slab in a roundabout does not prevent a heavy truck from straying off the right lane! To have fresh information on durability and cracking (working loads), and on the bearing capacity and failure mode (ultimate loads), displacement-controlled tests have been recently performed in Milan on four typical rectangular R/C slabs suspended along their short sides via corbels (dapped ends; size: 1.3×2.2×0.15 m [51×87×6 in.]). A transversely-distributed or concentrated load was applied either at mid-span (in the bending tests), or at 1/10 of the span (in the shear tests). The two slabs Type A are provided with longitudinal bent-up bars in the main body and hooks in the corbels. On the contrary, the slabs type B are reinforced via two continuous layers of longitudinal straight bars. Under the working loads, cracking never occurred, neither in bending nor in shear - to the advantage of durability - while above the working loads rather complex crack patterns formed in the D zones close to the corbels, particularly under the concentrated load, which brought in 3-D effects, with a limited reduction in the bearing capacity. Refining the reinforcement layout is shown - once more - to markedly improve slab performance, with little or no extra cost.