The towers for the Gordie Howe International Bridge continue to reach new heights and it’s the work done at ground level that has allowed the tower construction to progress.
This summer marked the completion of the final piece of the foundation for the towers in both Canada and the United States with a process known as post-tension work for the tie-beams that connect the tower legs.
Post tensioning is a technique used on large infrastructure projects to reinforce concrete and other material with high strength steel bars or a bundle of strands known as tendons. Post-tensioning tendons are high strength steel cables or strands inside plastic ducts or sleeves that significantly help reduce the structures weight and foundation load.
Frank Raji, the Director of Construction for Windsor-Detroit Bridge Authority, says the work is critical to the design and functionality of the bridge.
“The completion of the post-tension work not only allows tower construction to proceed as part of the design plan, it supports the towers built on land with a clear span over the Detroit River,” says Raji.
As part of the post-tension work, 31 steel strands are used in each of the tendons in the tower footings. There are 21 tendons in the footings for the Canadian towers and 25 tendons in the footings for the towers in the US. That means a total of 1,426 steel strands are used to connect the tower footings.
Each strand is 72 metres/236 feet in length and each metre or foot of the steel strand weighs 1.1 kilograms/2.2 pounds. In total, the weight of the strands in the bridge footings are 112,939 kilograms/248,988 pounds.
Workers used a multi-strand stressing jack, strand pushers and a grouting plant to complete the work and ensure the final force of the tendons met the design requirements.
“The cables pull the footings together, so they work as one and handle the tower loads and eventually the road deck,” adds Raji.
As part of the foundation work, six shafts were drilled into the bedrock for each tower leg to a depth of 36 metres/118 feet. That is the equivalent of a 10-storey building.
Once completed, the towers for the Gordie Howe International Bridge will stand at 220 metres/722 feet on each side of the Detroit River with the longest main span of any cable-stayed bridge in North America at 853 metres/0.53 miles.