There are seven bridges over the River Arno in the central area of Florence, of which only one (The Ponte Vecchio) is an original old structure, the remainder of the old bridges having been destroyed by the retreating German army at the end of World War 2. Of the new bridges, 2 are replicas of the original structure and 4 are of new design, but all are of interest.
The first and last of the seven structures are reinforced concrete arch bridges:
The Ponte di San Niccolo is an elegant single span designed by Riccardo Morandi and constructed between 1947 and 1949. It replaced a steel suspension bridge built between 1836 and 1837.
The structure has wide vertical cracks in the spandrel walls at both abutments, possibly due to thermal movements:
The Ponte Alla Vittoria is a 3 span bridge with flat concrete arches. The original bridge on this site was also a steel suspension bridge. The new bridge has an unusual strongly shaped deck, merging smoothly into the concrete piers:
The next bridge from the East is the Ponte alle Grazie, completed in 1953, replacing a 9 span arch bridge originally built in 1227 and rebuilt in 1345. The new structure is a 5 span reinforced concrete arch structure, but its form is clearly based on that of the adjacent Ponte Vecchio, especially in the relationship of the deck and piers:
The design of this bridge was subject to a competition, with some controversy about the use of reinforced concrete rather than traditional materials, described (in Italian) at: Ponte alla Grazie.
The remaining reinforced concrete bridge is the Ponte Amerigo Vespucci, which is described in the Wikipedia article as an arch, but is in fact a three span prestressed concrete structure:
The bridge construction was completed in 1957, replacing a temporary structure completed in 1949. Further details of the bridge design and construction are given (in Italian) at: Ponte Amerigo Vespucci
The two new bridges downstream of the Ponte Vecchio are both replicas of the original structures at their sites. The Ponte Santa Trinita is described in the Wikipedia article as the oldest elliptic arch bridge in the world, the previous bridge having been constructed in 1567 to 1569, replacing bridges built in 1252, 1333, both of which were destroyed by floods.
The Ponte alla Carraia is a 5 span segmental arch bridge completed in 1948.
Finally the sole remaining old bridge structure is the famous Ponte Vecchio.
Known more for the gold shops that still line the bridge than for any structural innovation, it is nonetheless an early example of a flat segmental arch construction, having been completed in 1345 with a maximum span of 30 m and rise of 4.4 m.