Steel Buildings in Europe

Part 2: Concept Design 2 - 51 (a) 1 2 3 (b) (c) 4 5 1 Concrete infill (screed / concrete topping optional) 2 Hollowcore slab 3 Transverse reinforcement 4 Concrete topping 5 Solid planks Figure 5.11 Forms of composite beams with precast concrete units (a) Composite beam with square-ended hollowcore slabs (b) Composite beam with chamfered-ended hollowcore slabs (c) Composite beam with precast planks The shear connecto rs and transverse re inforcement ensure transfer of the longitudinal shear force from the steel section into the precast concrete unit and the concrete topping. Com posite design is n ot perm itted unless th e shear connectors are s ituated in an end g ap (between the concrete units ) of at leas t 50 mm. For on-site welding of shear c onnectors, a practical m inimum end gap between concrete units is 65 mm. The shear connector res istance depends on the degree of confine ment and in situ concrete with 10 mm aggregate is often used. Hollow cores should be back-filled at the supports for a m inimum length equal to th e core diam eter to provide for effective composite action an d adequate fire resistance. Minimum fl ange widths are required to provide a safe bearing length for the precast units and sufficient gap for effective action of the s hear connectors – minimum recommended values are given in Table 5.5.