"The Maria Pia bridge (Ponte Maria Pia), commonly known as Ponte Dona Maria, is a railway bridge built in 1877 by Gustave Eiffel in Porto, Portugal. Built of wrought iron, its two-hinged crescent arch used to carry the railway to Lisbon for 353 metres (1,158 ft) across the River Douro at a height of 60 m (200 ft) above the river. When constructed it was the longest single-arch span in the world. It is no longer in use as a rail bridge, a modern replacement having been constructed in 1991.
In 1875 the Royal Portuguese Railway Company announced a competition for a bridge to carry the Lisbon to Porto railway across the river Douro. This was very technically demanding. The river was fast-flowing, its depth could be as much as 20 m (66 ft) when in flood and the river bed was made up of a deep layer of gravel. These factors ruled out the construction of piers in the river, so that the bridge would have to have a central span of 160 m (520 ft). At the time the longest bridge span was the 156 m (512 ft) of the bridge built by James B. Eads over the Mississippi at St Louis.
The Maria Pia Bridge during construction: the two halves of the arch have been connected, but their weight is still supported by cables.
Eiffel & Cie's design, priced at 965,000 French francs, was the least expensive of the four designs considered, around two thirds of the cost of the nearest competitor. Since the company was relatively inexperienced, a commission was appointed to report on their suitability to undertake the work. Their report was favorable, although it did emphasise the difficulty of the project:
"The complete study of a structure of this size presents great difficulties. The methods of calculation known up until now can only be applied in practise with the aid of hypotheses which depart from established fact to a greater or lesser extent, and thus render the projected results uncertain."
Responsibility for the actual design is difficult to attribute, but it is probable that a large part was played by Théophile Seyrig, Eiffel's business partner, who presented a paper on the bridge to the Société des Ingénieurs Civils in 1878. Eiffel, in his account of the bridge which accompanied the 1:50 scale model exhibited at the 1878 World's Fair, credited Seyrig, along with Henry de Dion, with work on the calculations and drawings.
The structure consists of a deck 352.7 m (1,157 ft) long, supported by two piers on one side of the river and three on the other, with a central arch with a span of 160 m (520 ft) and a rise of 42.6 m (140 ft).
Another innovation was the method of construction used for the central arch. Since it was impossible to use any falsework, the arch was built out from the abutments on either side, their weight being supported by steel cables attached to the top of the piers supporting the deck. The same method was also used to build the decking, temporary tower structures being built above deck level to support the cables. This technique had been previously used by Eads, but its use by Eiffel is a good example of his readiness to use the latest engineering techniques.
Construction started on 5 January 1876, and work on the abutments, piers and approach decking was complete by September. Work then paused due to the winter flooding of the river, and the erection of the central arch span was not started until March 1877 Construction was completed on 1 October 1877 and the bridge was opened on 4 November 1877 by King Luís I of Portugal and named after his queen, Maria Pia.
In 1982, the bridge was designated a National Monument by IGESPAR (the Institute for the Management of Architectural and Archaeological Heritage, a federal agency).
The bridge is often confused with the Dom Luís I Bridge, built nine years later and located a kilometre to the west, which bears a strong resemblance but has two decks.
In 1991, the bridge was superseded by the new St John's Bridge (Ponte de São João), designed by engineer Edgar Cardoso."
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