Megastructure - The Impossible Bridge Documentry by National Geographic

Rio–Antirrio bridge

The 2,880 m (9,449 ft) long bridge dramatically improves access to and from the Peloponnese, which could previously be reached only by ferry or via the isthmus of Corinth at its extreme east end. Its width is 28 m (92 ft) — it has two vehicle lanes per direction, an emergency lane and a pedestrian walkway. Its five-span four-pylon cable-stayed portion of length 2,252 m (7,388 ft) is the world's second longest cable-stayed deck; only the deck of the Millau Viaduct is longer at 2,460 m (8,071 ft). However, as the latter is also supported by bearings at the pylons apart from cable stays, the Rion-Antirion bridge deck might be considered the longest cable-stayed "suspended" deck.

This bridge is widely considered to be an engineering masterpiece owing to several solutions applied to span the difficult site. These difficulties include deep water, insecure materials for foundations, seismic activity, the probability of tsunamis, and the expansion of the Gulf of Corinth due to plate tectonics.

Due to the peculiar conditions of the straits, several unique engineering problems needed to be considered. The water depth reaches 65 m, the seabed is mostly of loose sediment, the seismic activity and possibility of tectonic movement is significant, and the Gulf of Corinth is expanding at a rate of about 30 mm a year. For these reasons, special construction techniques were applied. The piers are not buried into the seabed, but rather rest on a bed of gravel which was meticulously leveled to an even surface (a difficult endeavor at this depth). During an earthquake, the piers should be allowed to move laterally on the seabed with the gravel bed absorbing the energy. The bridge parts are connected to the pylons using jacks and dampers to absorb movement; too rigid a connection would cause the bridge structure to fail in the event of an earthquake. It was also important that the bridge not have too much lateral leeway either so as not to damage the piers. There is provision for the gradual expansion of the strait over the bridge's lifetime.

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