The Windsor Star
By Brian Cross
Because its towers can’t be planted in the Detroit River, the new government-backed bridge will have a tower-to-tower span that will rank it among the world’s longest.
The 1929 Ambassador Bridge ranks around 66th when it comes to suspension bridges based the 564 metres between its in-water piers. But the down-river DRIC bridge that’s supposed to be built and operating by 2020 is going to have a span of either 855 metres if it’s a suspension bridge (ranking it between 30th and 35th among suspension bridges, depending on the list) or 840 metres if it’s a cable-stayed bridge. It would be the longest cable-stayed bridge in North America and the 6th or 7th longest in the world.
The decision to not have any piers in the Detroit River goes back three or four years following discussions with the Canadian and U.S. coast guards as well as ship owners and captains, who said piers would interfere with safe navigation. The commitment was made as part of the environmental assessment. But that detail became suddenly prominent last week when MP Brian Masse (NDP – Windsor West) cited it in the House of Commons, as he argued against the way the federal government intends to build, finance and operate the $1-billion bridge through a public-private partnership.
“That decision to not have any structures in the water is the right choice,” Masse told The Star. But he said the decision means the bridge will have to be built a certain way – to go that distance between shores narrows the options down to either a suspension or cable-stayed bridge – perhaps limiting the number of qualified firms that are willing to get involved in the venture. “My concern is why are we doing a P3 (Public-Private Partnership) in the first place?”
Transport Canada spokesman Mark Butler said there is “significant” interest among private-sector companies interested in the DRIC project. “And we have confirmed this through a market sounding which sought expressions of interest.”
The next phase in the lengthy process starts as early as this week when geotechnical drilling will help determine how deep the on-land piers will go, and help determine what kind of bridge is ultimately built.
Shaohong Cheng, an associate professor of engineering at the University of Windsor, said it’s not important whether the piers are in the water or on land when it comes to building a bridge. In fact, piers in the water are more challenging because they require underwater construction.
“What really is important is how long is the span between the two towers,” she said. Anything over 600 metres requires either suspension or cable-spanned.
The longest bridges in the world are suspension, with the largest one, the Akashi Kaikyō Bridge in Japan, spanning 1,991 metres. Shaped like a stylized M, they employ two massive cables to hold up the roadway, that ride freely across the towers and transmit the load to anchors at either end.
If the DRIC bridge is suspension, its towers would be 140 metres high, slightly higher than the Fisher Building in Detroit and 20 metres higher than the Ambassador Bridge towers.
A cable-stayed bridge would have towers 250 metres tall, which is 30 metres higher than the Renaissance Center. Cable-stayed bridges also use cables to hold up the road, but these cables are attached to the towers. With a cable-stayed bridge all the load – from the vehicles, the weight of the bridge, the wind – is borne by the road bed and the towers, which transfer the load to the tower foundations. Their cables look like the ribs of an inverse fan, descending from the tower to the road bed. The longest in the world is the 1,104-metre Russky Bridge in Russia.
One factor in deciding between the two types is the soil conditions, because suspension bridges require very strong anchorages to bear the load of cables pulling horizontally. In very soft ground conditions, a suspension bridge might not be an option, said Cheng.
She said often a cable-stayed bridge is cheaper, but there are so many factors to consider when deciding between the two.
One big factor will be how various bridge models behave in wind, said Cheung, who researches wind-resistant design of bridges and buildings. Cheng said a bridge as big as this will require wind tunnel tests in which experts gather meteorological data for the area around the bridge from the last 40 or 50 years to determine the highest wind speed the bridge may encounter during its lifespan.
Transport Canada’s Butler said that “bottom line,” it’s been determined that either a cable-stay or suspension bridge will work at the DRIC site. It will be the P3 consortiums, that will do further tests including wind tests, to come forward with recommendations on which bridge is best.
All the major approvals for the bridge are in hand, and with most of the land required for the bridge and customs plaza on the Canadian side acquired, the land on the U.S. side now has to be appraised and purchased.
Following that, the government will be issuing a request for qualifications, for firms interested in the P3, said Butler. Following that there will be a request for proposals, with the start of construction expected at the end of 2015 or beginning of 2016.