New life for an old bridge
WINNER OF SUSTAINABILITY AWARD
Owner: City of Edmonton
CISC Engineer: DIALOG
CISC Fabricator/Detailer: Empire Iron Works Ltd. and Steel Design and Fabricators Ltd.
Steel Erector: Steel Design and Fabricators
General Contractor: ConCreate USL Ltd.
While Edmonton's Dawson Bridge has been in service for nearly a century, innovative technology used in its recent rehabilitation has turned it into a modern world leader.
The five-span riveted steel through-truss bridge was originally built to carry electric trains to a coal mine on the eastern bank of the North Saskatchewan River. Later converted to carry automobiles, the bridge currently accommodates 17,000 vehicles a day along with significant pedestrian and cyclist traffic.
After almost a century of use, the bridge needed significant repair including total deck replacement and truss repainting. Numerous truss members required strengthening or replacement to provide an appropriate level of safety and to extend the service life of the bridge.
The design team chose a lightweight composite steel plate and elastomer deck system using a technology originally developed for the marine industry and only recently applied to bridge construction. The system basically consists of two thin steel faceplates connected by an injected elastomer core, for a total thickness of only 45 millimetres in the case of the Dawson Bridge.
Says Kris Lima, a structural engineer with DIALOG and design consultant on the project: "By using this system, we were able to reduce by more than half the number of members needing strengthening or replacement to bring the bridge up to current safety standards.
"Only a handful of bridges have been built using this technology. The Dawson Bridge project is the first major project in the world of this scale to incorporate this innovative system."
Another innovation was the bridge's bolting system. It involves using splice plates to connect adjacent deck panels with countersunk bolts, allowing the panels to be quickly bolted into position on the bridge.