2013-2015 | Coquitlam & Surrey, BC – When the new Port Mann Bridge was completed in 2012, the old bridge needed to be removed. The original structure was built in 1962 and consisted of a three-span continuous steel tied-arch structure with an orthotropic deck system. Due to environmental concerns around the diffusions of known hazardous substances into the ecologically sensitive Fraser River, the removal process required a controlled deconstruction, in lieu of explosives.
The continuous tied-arch system was an exceptionally efficient structural system in its completed state. However, for all other temporary stages, the structure was unstable due to a lack of diagonal members. This necessitated a highly technical piece-by-piece removal, where the original bridge tied-arch was transformed into a cantilever structure through the use of stay cables and a temporary tower to allow for the dismantling through a reversal of the original construction sequence. The major challenge was to maintain the stability of the extremely vulnerable partial structure under construction equipment loads and dynamic winds. Access restrictions from the large rail yard under the south side-span required careful sequencing and strengthening measures to stabilize the structure once the connection with the anchor pier was removed. The team employed containment procedures at superstructure cutting locations (starting from the centre) as components were removed for recycling.
The team used a barge mounted crane and a pair of deck-mounted stiff leg derricks to facilitate bridge member removal. A significant challenge early in the deconstruction process was performing the initial relief cut in the arch ribs at midspan after the stay cables were installed and stressed. This highly controlled and technical process was the official conversion of a continuous tied-arch system into two cantilevers, since the arch rib was no longer continuous.
Working for the Kiewit-Flatiron contractor team, McElhanney was responsible for the detailed construction engineering of the bridge decommissioning, including:
- Development of the deconstruction process and sequencing
- Step-by-step deconstruction analysis using LARSA 4D
- Design and detailing of temporary works members required to strengthen and stabilize the partial structure at all phase
- Preparation and maintenance of the deconstruction manual, including cable jacking sequences and geometry control
- Evaluation of stay cable stressing results and survey data at all stages
- Field reviews
In 2016, this project earned an award of Merit from ACEC-BC.