The hydraulic vulnerability of infrastructure is sometimes manifested disastrously during extreme weather events. A watercourse, whatever its size, is in fact a separation between the two territories that often instead they need to communicate with each other. A bridge then represents a conjunction between the separate parts and, historically, has always been trying to realize the solution that would make the minimum structural impact, such as a natural shrinkage of the hydraulic section, less use of piers in the riverbed and minimization of the hydraulic free-board.
These conditions, optimal to join separate lands of the territory, are critical for the outflow of hydraulic stream rates and represent a major obstacle in case of serious events, just when the infrastructure is absolutely essential for civilian’s security.
In line with the latest regulations in the construction business, PAC always focused his attention on this matter, during flood bridges are subject to a number of damages that can go from the damage of the deck, yielding of the piers or the abutments, the backdown and the destruction of the backfilled access roads. The company, taking care of the design and construction of bridges, but also of viaducts, tunnels and moles, is continuously studying the best solutions that guarantee at the same time the lower hydraulic impact and the longer lifetime of the infrastructure.
For example, the original bridge in Ziano di Fiemme (Trento, Italy), Roda area, was an infrastructure with two spans of 18.5m, demolished and rebuilt taking advantage of solutions that are avoiding future damages related to the hydraulic vulnerability. The most important factor was to increase original free span to become 37m, furthermore the removal of the central piers allows the hydraulic free-board, space between the water level and the soffit deck, to be increased considerably. Therefore, the river upstream conditions will be safer and will be avoid the sudden wave of flood to reach the valley, in case of failure of the deck.
Finally, to be noted that the morphology of the river bed and also the relevant flow rate flood will be affected by the infrastructure location, and is important to consider that many Italian river bridges are having an increase hydraulic vulnerability more often even with less rain falls. Those old-style solution bridges have been designed and executed when the actual engineering solutions were not available, now days they give as the opportunity to reduce the structural criticalities and to avoid the interferences with natural water flow.