Experimental and numerical study of the ductility of open-rib and reentrant composite slabs

The most restrictive failure mode of steel–concrete composite slabs is longitudinal shear. The partial connection method (PCM) is a design method for longitudinal shear capacity limited to slabs showing ductile failure and assumes the complete yielding of the slab cross-section. Ductility is defined in Eurocode-4 in terms of additional strength after the first slip occurs, regardless of the total slip magnitude. This article shows that the slip behavior is significantly different depending on the shape of the sheeting profile. The slip magnitude in reentrant slabs can be large enough to drive the steel sheeting and the concrete to their yielding stresses since the two materials remain vertically clamped always. Conversely, in open-rib profiles, the slip mechanics cannot drive the materials to the yielding stresses since the vertical release of the two materials occurs earlier, when the slip exceeds specific values related to the embossments’ geometry, after which the vertical clamping is no longer possible. The results show that the vertical release between the concrete and the profiled steel sheeting is reached after the slip values about 2–5 mm in open rib profiles, whereas they remain permanently clamped in reentrant profiles. This paper demonstrates that the maximum load in open-rib slabs is related to the vertical release before the materials reach their yielding stresses. These findings are consistent with both the FEM and experimental tests presented and suggest the need to review the ductility definition in standards or the applicability of the PCM in open-rib slabs. The experimental campaign includes tests conducted at the Laboratory of Elasticity and Strength of Materials, LERMA, Universitat Politècnica de Catalunya, and external resources.Postprint (updated version