Failure scenarios of small bridges in case of extreme rainstorms

This contribution comes from the investigations carried out on recent flooding events occurred in Italian suburban areas. Those events, regarding minor roads, cause unexpected failure modes of existing bridges with reduced span (less than 10 m), whose construction and maintenance are not properly covered by standards. Three failure scenarios are here considered: the dragging effect on vehicles when they are crossing bridges (A), the erosion effect due to the overtopping of the bridge (B), and the erosion and the floating effect caused by upward buoyant force from Archimedes’ principle on the bridge slab (C). The described mechanisms of failure are paradigmatic to identify not only the structural collapses but also the service failure. In this sense, the ‘resilience’ of the small bridge is defined, in view to propose technical indications for maintenance and consolidation activities.