Steel Buildings in Europe

Part 2: Concept Design 2 - 56  A steel plate (typically 15 mm thick) may welded to the underside of an H section. This plate extends beyond the bottom flange by at least 100 mm either side, in order to support the precast concrete units.  A 20 mm fl ange plate (typical) m ay be we lded to half of an I section cut along the web. A structural concrete topping with rein forcement is recommended in order to tie the P.C. units together. The topping thickness should cover the P.C. units by at least 50 mm. I f used without a t opping, reinforcement s hould be provided through the web of the beam to tie the fl oor on each sid e of the beam together in order to meet robustness requirements. 1 Hollowcore concrete slab 2 IFB/SFB – beam 3 Column section Figure 5.16 Integrated floor beam (slim floor beam) and precast concrete units A com posite integ rated beam can be achieved by welding shear conn ectors (normally 19 mm diameter  70 mm long) to the top flange of the steel section. Reinforcement is then placed across the flange into slots prepared in the precast units, or on top of shallow precast units. If the beams are designed compositely, the topping should cover the shear c onnectors by at least 15 mm, and the precast units by at least 60 mm. A typical structural arrangem ent in wh ich the integrated beam s span 6 m and the P.C. units span 7,5 m is illustrated in F igure 5.17. In this cas e, th e P.C. units are 200 mm deep and a 60 mm concrete topping is used. The edge beam s are IPE, designed as n on-composite and are placed belo w the P.C. units. Nominal shear connectors are provided to m eet robustness requirem ents. In this case, th e slab can be cas t level w ith th e top of the beam, as shown in Figure 5.18. 5.7.2 Beam spans and design criteria Ideally, th e span of the precast con crete units and the b eam span should be optimised to produce a f loor thickness compatible with the beam depth. Beams loaded on one side only are relatively h eavy because of their torsional loading. Also, tors ional ef fects during construction will need to be checked. A central spine beam with precast units spanni ng to downstand edge beam s (beams located under the P.C. units, but co ncealed in the wall) will generally b e more economic than the P.C. units spanning along the building, onto a series of transverse spanning beams.