Steel Buildings in Europe

Part 4: Detailed Design 4 – 45 All floor solutions involving permanent formwork such as metal decking fixed by studs welded to the beams, with in-situ concrete infill, provide an excellent stiff diaphragm to carry horizontal forces to the bracing system. Floor systems involving precast concrete planks require proper consideration to ensure adequate transfer of forces if they are to act as a diaphragm. The coefficient of friction between planks and steelwork may be as low as 0,1 and even lower if the steel is painted. This will allow the slabs to move relative to each other and to slide over the steelwork. Grouting between the slabs will only partially overcome this problem, and for large shears, a more positive tying system will be required between the slabs and from the slabs to the steelwork. Connection between planks may be achieved by reinforcement in the topping. This may be welded mesh or ties may be placed along both ends of a set of planks to ensure the whole panel acts as one. Typically, a 10 mm bar at half depth of the topping will be satisfactory. Connection to the steelwork may be achieved by one of two methods:  Enclose the slabs by a steel frame (on shelf angles, or specially provided constraint) and fill the gap with concrete.  Provide ties between the plank topping and a local topping to the steelwork (known as an ‘edge strip’). The steel beam has some form of shear connectors to transfer forces between the in-situ edge strip and the steelwork. Figure 5.15 Possible connection between precast concrete plank and steelwork to ensure diaphragm action of the floor Appropriate attention needs to be given to the ‘load paths’ that transfer the end shears of the horizontal diaphragms in the vertical bracing or concrete core. It is frequently possible to ensure that the ‘end posts’ of the horizontal diaphragms (or trusses) are also the top ‘end posts’ of the vertical bracing. Where concrete cores resist horizontal actions, it is usually possible to tie the concrete diaphragms directly into the cores.