October 14, 2016 by Corinne Lynds
For only the second time in history, the suspended spans of a bridge are being replaced while keeping the bridge open to traffic. The first; was the Lions Gate Bridge in Vancouver, and the second is Halifax’s own Macdonald Bridge.
The $207-million project, fondly known as “The Big Lift,” is necessary to extend the life of the bridge and reduce maintenance. According to Steve Snider, GM and CEO of the bridge, after six decades the deck was starting to separate from the floor beams, causing a rough ride for bridge patrons.
The bridge, which remains open to vehicular traffic during the day, shuts down at 7 p.m. every night for construction, and then reopens at 5:30 a.m. before the morning rush.
The Big Lift includes replacement of the road deck, floor beams, stiffening trusses and suspender ropes on the suspended spans (2,500 ft. of the overall 4,418 ft. length). Once complete, much of the bridge infrastructure will be new, leaving
only the towers, main cables and anchors on the suspended spans as original.
Starting near the Dartmouth shore then working across the main span between the two towers, the bridge deck panels over the water were replaced overnight in 20-m lengths. The segments being replaced over land on the Halifax side are more complicated and require the use of a massive crane (these panels are only 10 m in length). As of September 19th, 30 of the 46 segments had been replaced. According to communications manager Alison Macdonald of Halifax-Dartmouth Bridge Commission, all deck segments will be replaced and the bike lane is on target to be finished by the end of this year.
As you might imagine, a job like this requires the coordination of efforts from several different teams in order to run smoothly night after night (see Team sidebar on page 32).
The bridge deck panels that were replaced over water required a lifting gantry to be positioned on the suspender ropes, and then the existing panel was lowered to a barge in the harbour. A new panel was then lifted into position in the same manner. One deck panel was replaced every three or four working nights in the beginning, but since April, the crew has increased from 35 ironworkers to 70, and two deck panels are able to be replaced at a time.
Pieter Webbink from Eagle Beach Contractors Ltd., (the firm catching the pieces of the old bridge deck as they are lowered onto a waiting barge) explained to On-Site back in June, that a lot of the initial delays were related to learning curve. “The first deck segment took 62.5 hours to replace, but the average is now down to about 15 hours.”
Over the coming months the bridge height will be adjusted to increase shipping clearance by 2.1 metres. And, in 2017 there will be paving and work on the expansion joints as well. A final, separate project will see a dehumidification system put in place to extend the life of the main cable stays.
Crossing during construction
The Macdonald Bridge is a critical piece of infrastructure in Halifax, and
closing it to traffic for an extended period of time was not feasible. The city, and emergency services, would not be able to handle the congestion caused by having only one bridge. With this in mind, the construction and engineering firms devised a schedule that means the work is mostly completed overnight, and the bridge is open to the public during the day. The bridge is closed six nights per week (Sunday through Friday) from 7 p.m. until 5:30 a.m. And in the 18 months that the project is expected to take, there will be approximately 12 full weekend closures.
While the bridge has remained open to traffic during construction, the bike lane and sidewalk were removed prior to the first panel being replaced primarily for safety reasons. The new deck is much lighter than the original deck. To carry out the project the weight on the existing bridge deck must be reduced to account for construction equipment and temporary connections at the construction face.
During construction, a 24-hour day shuttle service is being provided. It consists of three 17-passenger buses with bike trailers attached. Each bike trailer can accommodate 12 bikes. The service is free for users.
With files from the Halifax-Dartmouth Bridge Commission