Concrete Filled Steel Tube Arch: Fid-Bau Portal

Concrete Filled Steel Tube Arch

M. K. Tadros / A. F. Girgis

Ravenna viaduct spans a major route of the Burlington Northern Santa Fe Railroad. Approximately 60 trains per day pass under the bridge. There are very tight restrictions on the vertical clearance above the tracks, the horizontal distance to any pier, and the amount of time rail traffic can be interrupted. The bridge is 174 ft. long to span over 6 sets of rail tracks, two main lines and four sidings. Since this section of track is a major route for the railroad, the amount of time the tracks can be closed is limited to a few hours, and only a limited number of closures. Maintaining the existing road grade and providing the required vertical clearance above the railroad tracks limited the depth of the structure to 35 in. The old bridge was scheduled to be replaced because it was structurally deficient and functionally obsolete. The vertical clearance above the tracks was less than 23 ft, the horizontal clearance from the pier to the track was less than 13 ft, and the horizontal clearance at the south abutment was 8.5 ft to the track. In addition, the railroad wanted additional space on the south side to extend two side tracks through the bridge opening. The grade coming off the bridge to the north was 7% and touchdown was at the south end of town's main street. To solve all these concerns, a bridge with a long span and a very shallow superstructure depth was needed. The answer appeared to be a truss or a tied arch. This paper report presents a practical solution for the clearance limitation through utilizing a unique arch bridge system. The report describes in detail the rapid construction sequencing, and the laboratory tests performed at the University of Nebraska to clarify some of the design issues that the designers were facing. This prefabricated developed system is suitable for accelerated construction, as well as the constraint of working over live main railroad tracks.