ABSTRACT
The roof elements are characterized by a 10 m long span and a thin walled open cross section. The top horizontal slab is only 6 cm thick and is reinforced at the intrados with a wire fabric and 5 bars concentrated at the ends (1Φ6/20 + 5Φ8). The longitudinal reinforcement consists in 2+2 0.6” strands and 1+1 Φ10 4 m long bars, placed in the middle. They are simply supported at the ends and the acting loads are the dead weight (GΩ) and the snow loads. The precast covering structure uses TT beams which are longitudinally over-reinforced, but are transversally deformable. The two webs are interconnected by a very thin slab, only 8 cm thick, where the reinforcement location cannot be regarded as univocally determined. Even with a gross cover of 20 mm the transversal bending moment acting at the Serviceability Limit State greatly exceeds the cracking value: the bending moment caused by the only dead load of the whole structure (M = 8.09 kNm) is about the double of the one that causes first cracking. A drastic simplification that reduces the shear acting in the two webs to simply support reactions (Fig.3) allows the designer to neglect the redistribution that induces a torque in the webs and in the wings due to transversal deformability of the cross section and computes the transversal bending moment by means of pure equilibrium.
