By: Brian W. Budzynski
For Halifax, Nova Scotia, the Angus L. Macdonald Bridge has been an iconic structure for more than 60 years. Years that, as the bridge spans an occasionally rough and always popular Atlantic waterway (Halifax Harbour), had taken a significant toll. As noted in our May 2017 issue (“A new life for the ‘Old Bridge’”), when it came time to rehabilitate the bridge, project planners had a few options to consider, ranging from simple resurfacing to a full-scale conversion to a cable-stay bridge; ultimately, however, mere resurfacing did not address the more critical failure issues at stake, and conversion, aside from presenting too large a risk, would have knocked the bridge out of service for periods deemed unacceptable. The bridge handles approximately 20% of peak capacity traffic flow between Halifax and Dartmouth, some 45,000 vehicles per day.
Project manager Jon Eppell said in May, “Everything goes to gridlock if the Macdonald is taken out of service, so we knew we could not take the bridge out of service . . . or we would cripple traffic flow in the city.
“At the beginning of the ‘Big Lift’ project,” Eppell said, “we had three traffic lanes and two stiffening trusses, which are built-up steel members, not enclosed members, by which I mean we’re not dealing with I-beams, but with angles and plates assembled to create box shapes, but they’re open. Which means there’s been a lot of maintenance on them. The stiffening trusses are above deck, and on the outside of that is the sidewalk and bikeway. The original deck of the bridge was still in place from its original construction for about 25 ft of the deck width. It is a 3-in. steel grid deck with concrete in-fill. Water and salt had dripped over the edge for years, and we had corrosion of the top flange of the supporting beams, which were covered by the deck, so we had no way of accessing them to repair them. That was the trigger for doing this project in the first place. If we left it long enough, it would become a safety issue.”
A specialized gantry system made it possible to install pre-fabricated units 20 m long and about 120 tons each. Crews removed an entire deck piece, lowered it to a barge in the Harbour and brought up a prefabricated piece, then temporarily connected it to the existing deck and permanently to the new deck piece that was installed before it, unit by unit. The units were fabricated with the stiffening truss below the deck, not above it. As a result, they are protected from water and salt off the bridge deck.
Since May, crews set expansion joints on existing approaches and finished paving.
Eppell said, “Now we’re finishing the main cable dehumidification wrapping. We’ve made great strides. We’ll be testing very soon, and hopefully get it commissioned in December.”
Project: Angus L. Macdonald Bridge
Location: Halifax, Nova Scotia
Owner: Halifax Harbour Bridges
Designers: Cowi North American and Harbourside Engineering
Contractor: American Bridge Canada
Cost: $205 million CAN
Length: 1,346.6 m with 762 m suspended span
Completion Date: November 2017
About The Author: Budzynski is managing editor of Roads & Bridges.
