Egis (formerly Mcintosh Perry) was tasked with extending the service life of the 74-year-old Touchette Bridge over the South Nation River near Casselman, Ontario. The bridge was a 73 m long single-span Parker through truss bridge with a timber deck on steel stringers supported by steel floor beams.
The bridge was in poor condition with severe section loss in the steel floor beams and stringer deck system and extensive delaminations and spalls on its abutments. The poor condition had limited loads on the structure to 15 tonnes and the bridge was on the brink of closing. The Nation, a rural municipality boasting a population of just 13,000 inhabitants and an annual capital works budget of $5 million, sought our expertise to address a critical infrastructure challenge. The municipality had planned to replace the bridge but could not secure sufficient funding to cover the costs. The stakes were high. Failure to restore the bridge within the available budget would have had profound implications for the local agricultural community. With the nearest alternative crossing located 25 kilometers away, agricultural operations on either side of the bridge would have faced substantial disruptions, impacting both efficiency and livelihoods.
The client tasked us with designing a rehabilitation that would restore normal loading conditions and extend the service life of the bridge by more than 25 years.
During the teams initial site visit, to confirm the scope of work, the bridge team noted a concern with the south abutment which was not previously identified. The south abutment expansion joint was completely closed, and the deck end was pushing against the ballast wall even as the bridge contracted in colder temperatures. In addition, the south abutment uni-directional pot bearings had exceeded their movement capacity and the PTFE sliding surface had become dislodged. Following an assessment of the south abutment, it was concluded that the south abutment needed to be stabilized before removing the entire steel deck system and jacking the truss to replace the bearings.
These unexpected concerns made salvaging the bridge more difficult. This project exemplifies the challenges faced by small municipalities in managing large bridges and the ensuing economic complexities of their maintenance.
This paper will discuss the analysis of the truss and substructure, the stabilization of the abutment and the carefully engineered construction sequence that was developed to complete the $4.5M rehabilitation.
