One of the challenges the team faced in the design stage for the bridge was working with such a limited project footprint due to the spawning grounds to the north and a railway bridge to the south. The cable-stayed design turned out to be one of the best options in terms of minimizing environmental impact when compared to the alternative girder bridge option. “We did an evaluation on the two different options,” Weiss explained. “The river is a very fast-flowing river, and to try to erect some of these long-spanned girder bridges off barges in this area was just not very practical due to the amount of water that goes through this area.”
For the construction of the bridge, the team adopted a balanced cantilever method of construction, with the piers going up first and then the deck is moved out on each side, simultaneously expanding toward the east and west abutments. Everything above the deck surface was made out of precast concrete, which Weiss explained was for two reasons: for the structure’s durability and to speed up the construction timeline due to the limitations of days with good weather in the region. The bridge deck was all precast concrete on steel girders, which were joined together using an ultra-high performance concrete called Ductal, supplied by Lafarge, which allowed for a small and efficient construction joint to join the precast deck panels together. The execution for the ultra-high performance concrete proved to be challenging for crews due to the way it was mixed with custom-made mixers, and the fluidity of the fresh product required watertight forms to prevent leaks.
As the bridge is the first cable-stayed structure in Ontario, the precast towers serve as a signature aesthetic feature. The Nipigon River Bridge is the only one of its kind in North America with precast towers as high as this, at 50 meters high from deck level and 75 meters high from ground level. The three towers on the bridge are each composed by 24 segments precast with match-cast technique to ensure the verticality during installation, which included post-tensioning bars and strands to ensure temporary and permanent stability. One of the main challenges of the project included the logistics for delivery of the precast elements to such a remote location. The precast towers were cast in Calgary, Alberta—2,135 km away from the site; the steel structure was manufactured in Laval and Quebec City, Quebec—1,700 km away; and the precast slabs for the deck were made in Winnipeg—800 km away.
The team also faced challenging weather conditions, with temperatures ranging from -45°F to -85°F at certain points during the construction process, which would significantly impact the construction schedule. “We had a very cold first winter when construction of the footing was supposed to be done,” Weiss said.
With the help of a contractor with advanced knowledge of newer construction means, methods, and materials, the Ontario Ministry of Transportation was able to open all four lanes of a first-of-its-kind bridge across a critical roadway by the Fall of 2018.
