Il crollo singolare di un tegolo prefabbricato anni ’60: le cause e l’intervento di rinforzo

This paper describes a collapse of a thin-webbed roof element, recently occurred in a quite important building in Northern Italy. The roof ele-ment consisted in a open V section beam, characterized by one prestressed bottom chord, two thin wings (70 mm thick) and two minor top chords. The total height of the member was 1300 mm and the span 17,3 m. The mode of collapse, its reasons, the whole set of diagnostic investigation on site, as well as the evaluation of the existing structure prior any strengthening are discussed. The unrestrained transverse flexure, the small diameter of transverse bars in the wings and the corrosion induced by the transverse flexure crack along the interface between bottom chord and wing were detected as the main reasons of the collapse. A suitable and effective strengthening tech-nique (by means of a detailed system of steel ties and beams) is proposed aiming at being mainly reversible, minimally impairing the building integrity, easily put in place and allowing an effective utilization of the building during restoration. Finally, a reinforced full-scale prototype is tested up to a deformation of about 0.01 the span, showing therefore a rather consistent ductility with the consequent possibility of giving warning prior to collapsing.