Dynamic tests of the Santarem cable-stayed bridge

The Santarem cable-stayed bridge is a road bridge that crosses the Tagus River near the city of Santarem. It is located about 3.5 km downstream from the old steel truss bridge (D. Luis bridge), built more than 100 years ago, and that was already insufficient for the increasing traffic and loads that had to cross it. The new bridge has a total length of 570 m with a central span of 246 m. The bridge deck has a cross-section formed by a 10.0 m by 2.5 m hollow rectangular shape caisson with an upper lateral slab and pre-cast concrete bracing's. The two masts have a height of 50 m above the deck and are in reinforced concrete up to the level of the first cables, and from there on have a steel-concrete composite structure. Before being opened to the traffic, the new bridge was subjected to static and dynamic load tests. This paper describes the dynamic tests that were conducted on the structure and that consisted in vibration measurements with the bridge being crossed by loaded trucks and also in tests with the trucks passing over a wood plank in order to apply an impulsive load to the structure. The paper describes the testing procedure and the analysis techniques that were used to process the measured accelerations. The characteristics of 32 natural vibration modes of the bridge are estimated from the tests data and are compared with the ones evaluated with a finite element model.