Prefabricated Bridge Pilot Launched

Ministry of Transportation (MTO) Staff in the Structural Section of Southwestern Region showed their innovative character when they proposed a prefabricated bridge pilot project for the Mull Road Underpass west of London. This bridge is a 4-span slab on steel girder bridge over Highway 401 with an expansion joint at each pier and abutment.

The project was comprised of a complete deck replacement using prefabricated full width and full depth deck panels and refurbishing of the existing steel gird ers. In addition to casting the parapet walls with the precast slab panels, the design also incorporated a unique "link slab" detail which eliminated the expansion joints at the abutments at a lower cost than all previous designs.

The contract specified that the precast facility be certified by the Canadian Standards Association (CSA) for the production of precast structural elements. The contractor, Facca Incorporated successfully obtained CSA certification for a temporary precasting plant located near the project limits.

Each panel was precast with exacting precision and then transported to the bridge. Traffic on Highway 401 was reduced to one lane while a 600 ton crane erected the panels with ease at an average production rate of 20 minutes per panel. Leveling devices, cast into the slabs, allowed field adjustment of the panels to insure proper positioning. Once in place, shear studs were installed on the steel girders through open pockets cast into the slabs. The panels are connected together via mechanical rebar splices and concrete filled 300mm wide closure strips. Outside ribs or pillars at the exterior face of the parapet were added at closure strips adding a pleasing aesthetic feature to the new structure. Given the right circumstances and more experience, deck panels for a similar bridge could be erected in a single day.

The contributions and support of staff from many areas including Planning & Design, Traffic, Contracts, Bridge Office and McCormick Rankin Corporation were most instrumental to the success of this innovative project.

"Using prefabricated bridge elements and systems mean that time-consuming formwork construction, curing, and other tasks associated with field fabrication can be done off-site in a controlled environment without affecting traffic", states Gerry Chaput, Chief Engineer/Director, and Highway Standards Branch.