Two Bridges over the river Arno in Florence, Italy
Ing. Roberto de Marco
In the outskirts of Florence, in scenery glorified by the magnificent city and its arch bridges in a harmoniously constructed landscape, the construction of a new highway that crosses the River Arno in 2 places is envisioned.
In order to minimize the visual impact of the construction and its implementation area, the solution adopted was the construction of lateral contention walls in reinforced soil throughout its extension (approximately 1220m).
Near the crossings of the river, these walls are of reinforced concrete and emerge over the water to overcome the imposed spans.
The structure of the bridges is formed by a section in coffin with variable height, in which the web appear in the same alignment as the contention walls, and in which the inferior flange defines an arch over the river, whereas the superior flange accompanies the highway elevation. In the central zone of the span, the two flanges are forged in order to form a voided slab section with circular tubes. The structural behaviour of the bridges resembles on one hand an arch of equal leg round-edged tee iron and on the other hand it resembles a bi-directional beam of variable inertia, being closer to one or the other, depending on the rigidness of the foundations.
The bridges ought to be constructed through the successive advance of cantilever, from the bank of the river, balanced with counterweights over the foundations.