Designed and built under the leadership of Campenon Bernard SGE, a number of challenges stood in the way of the project. Since it opened, it has been durably contributing to the development of Lisbon’s southern bank, while alleviating local traffic congestion. Let’s look back at the project.
The clock was ticking
When the Portuguese government issued its international call for tender, it made it clear that the bridge was to be inaugurated in time for the March 1998 Lisbon Universal Exhibition. With work starting up in January 1995, the deadline proved very tight, particularly in view of the project’s technical complexity. And yet the move paid off and the Vasco de Gama Bridge was delivered on time. A source of national pride, the engineering structure also won the award for civil engineering at the Hispano-American Architecture and Civil Engineering Biennial in Madrid in 2000.
In addition to an extremely tight construction schedule, the Vasco de Gama bridge combined a number of other challenges. Due to its unprecedented length of 17 km, the curvature of the earth had to be taken into account and appropriate technical and technological solutions had to be devised. In addition, the structure was designed to withstand earthquakes 4.5 times stronger than the one that razed Lisbon to the ground in 1755. Finally, the design of the bridge, with cable-stays reaching up to 824 metres, allows it to withstand wind speeds of up to 250 km/h.
To span the 17 km of the Tagus, the bridge was segmented into five different parts: four viaducts and a cable-stayed bridge, in addition to the interchanges. Given the tight deadlines and the length of the structure, a unique staging programme and satellite coordination system was set up. Different solutions work in combination to protect the structure from seismic risks: the northern viaduct is equipped with a shock absorber system capable of absorbing the effects of displacement. As for the deck of the cable-stayed bridge, it is not fixed to its pylons, which allows it to move laterally and longitudinally. Its flexible piers were designed for long periods of vibration. As for the piers of the central viaduct, they are equipped with hydraulic couplings which allow the bridge to move when in use but block it in the event of an earthquake.
An innovative approach
The bridge is also noteworthy in terms of its impact on the environment. Novel measures were taken at the time which contributed to promoting a new approach to assessing the environmental impact of the structures. Noise barriers, scour protection systems to protect the canal pier base and stormwater treatment basins were built in an effort to optimise and limit the impact of the bridge. On the southern bank, particular care was taken to conserve the Samouco salt marshes. These wetlands are a nature reserve and are vital to hundreds of species of birds, fish, crustaceans and molluscs. As part of the project, a new 400 ha reserve was created. In the spring of 1995, work was suspended for three weeks to allow for the passage of migratory birds.