Steel Buildings in Europe

Part 2: Concept Design 2 - 54 (400 mm or deeper). An exam ple of long span precast concrete units being placed on steel beams is shown in Figure 5.13. Shelf angles are bolted or welded to the beam web, with an outstand leg long enough to provide adequate bearing of the precast unit and to allow installation of the units under the top flange of the beam s. Precast concrete u nits are generally grouted in position. The P.C. un its may have either a screed (which may be structural), or a raised floor. Figure 5.13 Long span precast concrete units being placed on steelwork Temporary late ral b racing is of ten requir ed to lim it the ef fective leng th f or lateral torsional buckling of the beam during the construction stage when only one side is loaded. In order to meet robustness requirements, mesh and a structural topping may be required, or reinforcem ent concreted into hollow cores and passed through holes in the steel beam web. Tying may also be required between the concrete units and the edge beams. 5.6.2 Beam spans and design criteria Construction stage loading (precast planks on one side only) must be considered. Tem porary bracing m ay be required. Beam s loaded on one sid e only in the perm anent condition should designed for the applied torsional moment. When the top flange of a beam supports precast planks, th e minimum flange width is 180 mm to allow for m inimum bearing and a 30 mm gap between the P.C. units, as illustrated in Figure 5.14. Shelf angles should project at least 50 mm beyond the beam flange. When shelf angles are provided, 2 5 mm clearance is req uired between the end of the concrete unit and the beam flange, as shown in Figure 5.15.