Transportation Award of Excellence
Mill Creek Ravine Pedestrian Bridge Rehabilitation ISL Engineering and Land Services
42
CANADIAN CONSULTING ENGINEER
CCE_SPETOCT21_LAZ.indd 42
widening the bridge decks to meet current design standards for multiuse trails. New handrails were also designed to meet current safety standards for pedestrians and cyclists, but also to match the architectural style of the timber bridges. In these ways, ISL was able to maintain the original character of the bridges. Reducing repairs Timber rotting issues had been an ongoing maintenance challenge for the city. The existing timber pier columns were consistently rotted just below ground level and piers in the creek were in even worse condition. All foundations were converted to a concrete pile-and-cap design that elevated the timber just above
“They preserved the heritage of the structure and maintained its regional character. A great example of collaboration with a local neighbourhood.” - Jury
grade. The team also removed the timber pier columns from the creek and replaced them with a timber truss span designed to maintain the authenticity of the historic bridge appearance. Bridge decking had also been a maintenance concern for the city. The underlying problem was sandwiched layers of timber placed over the historic rail ties, which trapped moisture and promoted rotting. Addressing this concern, ISL designed a free-draining bridge decking solution, with large timbers connected from below the deck using galvanized hardware. Minimizing disturbance Trail closures were necessary to complete bridge construction. A
PHOTO COU RT E SY I S L
T
he City of Edmonton wanted to maintain the functionality of the Mill Creek Ravine trail system by extending the service life of its pedestrian bridges. Built in 1902, three of the bridges were originally part of the Edmonton, Yukon and Pacific Railway (EY&PR). The trestle bridges were converted for pedestrian use in the 1970s. Community engagement sessions emphasized the importance of preserving the heritage value of the structures. Thus, retaining part of the original ‘building fabric’ in the final construction was a key objective of the design process. To achieve this goal, the bridges were completely dismantled and each piece of timber was carefully graded and catalogued. This step added a significant challenge to the construction process and required a high level of co-ordination between ISL and the project’s prime contractor, Alberco Construction. A timber resistograph microdrill was used to determine which timbers could be salvaged. In the end, approximately 20% of the original timbers were salvaged and included in the final bridge construction. Additionally, ISL had to consider safety improvements to meet current requirements. This included
September/October 2021
2021-10-18 10:14 AM
CCE_IS
