Composite Slab Cantilevers

Safety over performance

Maximum unpropped slab cantilevers are not entirely based on the performance of the deck or slab. The figures are based on the safe distance of an arm extended through the edge protection system (assumed to be located on the beam top flange) avoiding the risk of working unsafely beyond the edge protection.


This rule is, however, subject to the type of edge protection system being used.


When designing deck cantilevers, the following should be noted;

  • A maximum cantilever length of 450mm (from toe of beam) can be safely installed when the deck spans perpendicular to the support.
  • For cantilevers greater than 450mm, suitable edge protection positioned outside of the slab edge position should be provided to allow safe installation. Contact the SMD Technical Team as temporary propping may also be required subject to the adjacent deck span and where the cantilever length exceeds 600mm.
  • Cantilevers in the steel deck cannot be achieved where beams are pre-studded.
  • Decking cannot be cantilevered where the sheet spans parallel to the supporting beam, however edge trim is typically suitable to achieve the desired detail (Refer Fig.4.7b).  The maximum overhang in these situations is governed by the edge trim type and thickness used.
  • The decking and/or edge trim provides formwork only to the slab overhang.  Should there be a high loading applied to the cantilever, the slab reinforcement (mesh or bar) may need to be increased to provide adequate slab resistance.

When designing cantilevers and edges to voids, consider the use of VoidSafe®, an alternative void solution with specially manufactured trim to provide support for the VoidSafe® protection system…

VoidSafe™ Protection System can significantly improve site logistics and access throughout the floor area.

For more information on this topic, see TGN Sections 4.7 and 4.8 specifically relating to this topic.

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