Steel Buildings in Europe

Part 2: Concept Design 2 - 41 Figure 5.1 together with their typical sl ab depths. A ‘targe t’ slab depth of 130 mm is often used for 50 or 60 mm deep deck profiles, increasing to 150 mm for 80 mm deep deck profiles. Steel thicknesses of 0,8 mm to 1,2 mm are used depending on the deck spans. The decking is normally designed to support the wet weight of the concrete and construction loading as a continuous m ember over two or three spans, but the composite slab is normally designed as sim ply supported between beam s. Sufficient com posite a ction occu rs that it is genera lly the constr uction condition that controls the m aximum spans that can be designed. Unpropped decking is preferred for reasons of speed of construction. The secondary beams in the floor grid are supported by primary beam s. These beams are usually designed as composite, but edge beam s can be designed as non-composite, although shear connectors m ay be used for structural integrity and wind loads. A typical example of a composite beam used as an edge beam is shown in Figure 5.2. 110 - 130 130 - 150 140 - 170 Figure 5.1 Decking profiles used in composite construction The shear connectors are norm ally site-welded through the decking to provide a secure fixing to the beam, and to enable the decking to provide restraint to the beam during the construction stage. Mesh reinforcement, normally of 140 mm to 200 mm 2 /m cross-sectional area, is placed in the slab to e nhance the fire resistance of the slab, to help distribute localised loads, to act as transverse reinforcement around the shear connectors and to reduce cracking in the slab over the beams.