Completed in 2006, the Puente Rio Tajo is one of two large arch bridges on the new A-66 Autovia Ruta de la Plata that crosses Spain’s massive Alcántara reservoir. The other crossing is over the Almonte River arm 8 miles (13 kms) to the south. Unlike the stayed cantilever method used to construct Almonte, the entire length of each half span of Tajo was built vertically above the foundation and then carefully lowered out over the river and closed at the crown in one well orchestrated maneuver. After the first of the two parallel spans was closed, oscillations from a 12 mph (20 km) wind began to push the arch up and down in a deformation pattern that saw one side of the arch rising as the opposite side was falling. Interestingly, when the wind blew above 19 mph (30 kmh), the problem disappeared. The situation was resolved by welding metal flaps or deflectors along the edge of the arch ribs.


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