About the support of steel decks

The bearing length is the longitudinal length of steel decking or slab in direct contact with the support. In each case, this length should be sufficient to satisfy the following relevant criterion. For decking, it should be sufficient to avoid excessive rib deformations, or web failure, near the supports during construction. For the slab, it should be sufficient to achieve the required load carrying capacity of the composite slab in service. 

The recommended bearing lengths and support details differ depending upon the support material (steel, concrete, etc.), and they are different for interior and exterior (end) supports. 

Steel or concrete supports - Composite slabs on steel or concrete supports should have minimum bearing lengths of 75 mm for the slab, and a minimum end bearing length of 50 mm for the decking (see Figure 1(a) and Figure 1(b)). For continuous decking, the minimum overall bearing length should be 75 mm. 

Masonry and other support types - Composite slabs on supports made of materials other than steel and concrete should have a minimum bearing length of 100 mm for the slab and a minimum end bearing length of 70 mm for the steel decking (see Figure 1(c) and Figure 1(d)). For continuous steel decking, the minimum overall bearing length should be 100 mm.