Vasco da Gama Bridge
Vasco da Gama Bridge, cable-stayed bridge with approach viaducts that crosses over the Tagus River estuary in Lisbon, Portugal. Spanning 17.2 km (10.7 miles), the structure was the longest bridge in Europe at the time of its inauguration. It was surpassed by the controversial Crimean Bridge (also called the Kerch Strait Bridge), which was formally opened by Vladimir Putin in 2018. The Crimean Bridge spans 19 km (12 miles) and was damaged by an explosion in 2022.
In preparation to host the 1998 World’s Fair (Expo ’98), Lisbon underwent the city’s biggest renewal project since the rebuilding that followed the devastating Lisbon earthquake of 1755. With regular traffic exceeding the capacity of the 25th of April Bridge, government officials put out an international call in 1991 for plans for the design, financing, construction, and operation of a second bridge over the widest part of the Tagus River. In 1994 the concession consortium Lusoponte, comprising Portuguese, British, and French companies, was awarded the contract with an extremely short deadline that stipulated that the new bridge be completed in time for the World’s Fair. In exchange, Lusoponte gained exclusive control of toll collection for both of Lisbon’s bridges for the next 40 years. Construction started in 1995, and the Vasco da Gama Bridge was inaugurated on time on March 29, 1998. It was named in honour of the 500th anniversary of the discovery of a sea route between Europe and India by explorer Vasco da Gama in 1498.
Given the speed of its construction, its astounding length, and its safety features, the bridge is an impressive work of engineering. Running north-south, the structure accommodates six lanes of automobile traffic and allows vehicles to bypass the city centre; it can be further expanded if additional capacity becomes necessary. The iconic cable-stayed portion of the bridge was built to facilitate the passage of ships on the river, and its deck is 47 metres (154 feet) above the water at high tide. It has a central span of 420 metres (1,378 feet) and side spans of 203 metres (666 feet) in length. The attractive H-shaped north and south pylons rise to 150 metres (492 feet) in height and serve to anchor the steel cables.
The remainder of the bridge consists of four approach viaducts, each built by separate companies as part of the contract consortium. The North Viaduct serves as the land connection from the more urban bank of the Tagus River and is 488 metres (1,601 feet) in length with 11 spans. Next is the Expo Viaduct, which runs 672 metres (2,205 feet) in length with 12 spans. On the other side of the cable-stayed bridge is the longest section, the Central Viaduct, spanning 6,351 metres (nearly 4 miles) with 80 spans. The deck of this viaduct is less than 14 metres (46 feet) above water level for most of its length but rises to 30 metres (98 feet) over two navigation channels to accommodate medium-sized vessels. Finally, the South Viaduct, some 3,825 metres (2.4 miles) in length with 84 spans, crosses the Samouco Salt Pans, an environmentally sensitive area for birds. Throughout its entire length, the lights of the bridge are tilted inward toward the roadway to reduce light pollution to protect the habitats found along the river and estuary.
Given that the city lies near an important fault line, the bridge was made to withstand an earthquake stronger than the 1755 earthquake that destroyed the city and killed as many as 60,000 people. It was also designed to resist winds of 250 km (155 miles) per hour. The cable-stayed portion of the bridge is built on two flexible piers with foundations penetrating 95 metres (312 feet) below sea level that are meant to withstand a ship collision. The deck is not fixed to its pylons, allowing it to move both sideways and lengthwise to accommodate wind and seismic activity. The North Viaduct portion of the bridge has shock absorbers for longitudinal shifts, and the remaining viaduct piers have hydraulic couplings to accommodate seismic activity. The piers along the navigation channels of the Central Viaduct are also meant to withstand a ship collision.