Dynamic Identification of a Historic Railway Riveted Bridge

This work includes the dynamic identification of a historic steel railway bridge after its restoration process, relocation some 100 km from its original location, and installation in a new location as a pedestrian footbridge. The bridge has a span of 21 m and a useful width of 2.9 m. Its main structure consists of two Pratt beams, connecting the crossing area with the lower chord of the footbridge and not having a connection between the two beams laterally at the top. On the sides of the bridge there are two 0.75 m wide walkways, originally intended for maintenance, but nowadays two water pipes have been installed. For the Operational Modal Analysis (OMA), 12 seismic accelerometers have been installed on the structure in order to determine the main bending and torsional frequencies and their associated modal shapes. These results have been compared with those obtained from a finite element model that has served as a basis for designing the location of the accelerometers. In the dynamic identification, the change in the bridge’s own frequencies has been observed with the pipes full of water and empty, as well as the importance of the lack of connection between the upper chords of the trusses that make up the bridge, the fundamental mode of the bridge being dominated by that of these trusses outside its plane. In all the studies analyzed, it has been observed that the structure’s main frequencies are far from the usual frequencies that can be generated by pedestrians walking or running and therefore will not present dynamic interaction.