Two Linden Comansa tower cranes are helping to build a 3,157 m long suspension bridge across the bay of Cádiz in Spain.

The €300 million (US$ 404 million) bridge, named La Pepa, will cross 1,655 m of water when it is completed in 2011. It will connect the city of Cádiz, on a narrow peninsula at the end of the bay, with the rest of the province. It will also alleviate traffic congestion on the existing Carranza Bridge which has 35,000 vehicles crossing it each day.

At 30 m wide, La Pepa will carry a three-lane highway and two railway lines. Maximum height will be 69 m, making it one of Europe's tallest bridges, while its span will be 540 m. Two 180 m tall towers will hold the 176 suspension cables.

The main towers make up two of the 36 columns, 12 of which are erected in the sea. The pair will be almost identical: one is on a port dock, 181 m tall, and the other is positioned in water and stands 187 m tall.

Construction company Dragados is using two Linden Comansa 21 LC 400 flat top tower cranes to build these structures. They have a lifting capacity of 18 tonnes. Jibs are up to 80 m long and are capable of taking 3 tonne loads at the tip. The cranes have 110 kW hoist motors to keep up with the speed of the work, says Comansa.

Complex systems

The two cranes need to be climbed periodically to raise their height to 195 m. This height and the inverted Y-shape of the towers, led Comansa to design a complex system of tiebacks. This creates a distance of up to 37 m between the tower and the mast section of the crane on the last level. Tower 12, over the water, will have four levels of tiebacks while the other main tower, 15, will have five.

The crane on tower 12 has been erected on the base of the column, just a few metres above sea level. For the erection a mobile crane on a large boat was used. At the beginning of the work, the tower crane was erected at a low height and is being jacked up as the job requires.

The same boat is being used to deliver all material needed for the construction of the tower and acts as a loading area for the crane.

The bridge designer, Javier Manterola, is one of Europe's most famous bridge engineers, says Comansa, and has been awarded Spanish and international prizes. During the first steps of the project the viaduct was named Bridge of the 1812 Constitution, as a tribute to Spain's first set of laws. In the end, however, it was renamed La Pepa, a popular term used to describe the constitution.

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