CN Bridge J448.34
over Tallahatchie River
Client: Canadian National Railroad
Location: Riverdale, Illinois
Construction Cost: $5.2 Million
The Canadian National (CN) Railroad Bridge crosses the Tallahatchie River using five deck plate girder spans and one 150-foot truss span. This 550-foot crossing was reconfigured in 1908 to replace four steel truss spans. This historic rail line was once known as the Mississippi Central Railroad and played a vital role in the Civil War.
In 1993 a derailment partially damaged the truss. Temporary reinforcements were applied to the truss members by the railroad and trains were slowed when crossing the span. Bowman, Barrett & Associates Inc. (BB&A) was contacted by CN in 2004 to provide permanent repair details and construction procedures. In addition to the damaged main support joint and bearing, sections of the adjoining end post, end floor beam, and bottom chord also needed to be replaced. The railroad requested the repair of the weathered concrete pedestals underneath the damaged bearings.
BB&A proposed in-kind replacement of the partially damaged truss members. The end post, bottom chord and end floor beam splices were designed to make field repairs as simple as possible by minimizing field bolting. BB&A also proposed replacing the bearing pedestals with precast concrete blocks to minimize outage time. All of the new built-up structural members, splice plates and bearing blocks were completely detailed.
In order to replace the damaged elements, the span needed to be jacked. BB&A designed jacking towers to be installed in the river in order to lift the damaged end truss at an intermediate panel point. A work platform connected to a pier was integrated into the design.
The construction procedure has proved challenging, as other minor repairs were also necessary on the destroyed portal frame and several knee braces. Proximity to adjacent spans has limited options. The construction sequence was chosen to make repairs in a timely manner while the long truss span was in a jacked position.
|
