February 26, 2009

At left, the suspension bridge nears completion in 1844. Its narrow deck quickly made the bridge inadequate. At right, this is the fourth version of the bridge which is still in use today. This photo is from the late 1920s and shows the steel-truss structure nearing completion. The masonry arch at the left is one of the two original stone arches, both of which are the focus of the present examination of the bridge.

Historical Construction

After thorough inspection, Chaudière Bridge awaits its fate

KORKY KOROLUK

correspondent

OTTAWA

The first bridge built between Ontario and Quebec is undergoing detailed examination to determine whether it is to be rehabilitated or replaced.

Chaudière Bridge, which crosses the Ottawa River just below Chaudière Falls, was closed for a week in December when inspection revealed deterioration in its two stone masonry arches. It reopened after a more detailed inspection, but is restricted to one lane of traffic in each direction, with a speed limit of 40 kilometres per hour and a load limit of five tonnes.

A federal public works department spokesman said at the time that although there has been deterioration in the arches, there is no visible sign of the sort of stresses that would indicate structural overloading.

A ministry spokesperson confirmed earlier this month that the type of stone used in the arches can deteriorate over time because of water and salt infiltration. She added that 180 years of freeze-thaw cycles have also contributed to the problem.

Spokeswomen Céline Tremblay said detailed computer modeling is under way to determine whether full use of the bridge can be resumed. The findings, she said, will help decide about rehabilitating or replacing the bridge or parts of it.

The models will allow engineers to examine in detail the behaviour of both arches when under load. The work will take three or four months, she said.

In this aerial view looking downstream, Quebec is on the left and Ontario on the right. Easily visible is the curved dam around the head of the falls, the white water and spray of the falls. The present steel truss span is the most visible, but several of the crossing’s eight spans can be seen. The bridge in the middle distance is the Portage Bridge.

A decision about the ultimate fate of the bridge — repair or replacement — will be made in about six months.

The Chaudière is one of five bridges over the Ottawa River in the city, and one of only two that can accommodate the hundreds of heavy trucks that traverse the region every day.

Although referred to as the Chaudière Bridge, it is made up of eight spans that leapfrog from island to island across the river. Two of the spans are of stone masonry, and it those arches that are now causing concern. They were built in 1826-28 as part of the original chain of bridges.

Although the stone arches have withstood 180 years of use, the more visible truss spans bridging the main river channel have had a somewhat checkered existence.

All crossed the Big Kettle, an area of deep, turbulent water just below the falls.

Although bridging the Big Kettle was difficult, the site was chosen because the small islands and rocky outcroppings made possible a crossing of eight relatively short spans, rather than a single long one.

The bridge was necessary because the men and materials needed for the early work on the Rideau Canal were available only in Wrightsville (later Hull, then Gatineau), on what is now the Quebec side. There was little on the Ontario side. The community of Bytown (later Ottawa) was still a few years in the future.

The bridge was important, too, as a symbolic union between Upper and Lower Canada.

That is why the first bridge, a handsome wood truss structure, was originally called the Union bridge.

Engineer John Mactaggart, looking at the completed bridge in 1828, said simply: “There it stands, and likely will for a length of time.”

That led historian Jonathan Vance, in his book, Building Canada, to comment that it “was hardly a ringing endorsement.”

Within a few years it had begun to deteriorate. It was reinforced in 1834, but just two years later, had to be closed to vehicles.

A good thing, too. Just 13 days after the closure, it collapsed into the Big Kettle.

After several years with nothing but ferry service, a new bridge was opened in 1843. A suspension bridge designed by Samuel Keefer, it was once described as the most daring Canadian engineering work of its day.

It had stone tower piers holding the suspension cables, and a deck that was stabilized with wooden trusses.

But it was only 20 feet wide, and was replaced in 1889. The new bridge was a steel truss structure built by the firm of Rousseau and Mather. But as loads increased, so did worries about the bridge, and by 1914 it was the next bridge to be declared inadequate.

That led to a contract awarded to Dominion Bridge, of Lachine, Que., in 1919, to build a new steel truss span. Ninety years later, it’s still in use.

The two stone arches currently being studied are important to history buffs because they are part of the original crossing. But there is another reason. They were built by Thomas McKay, the mason who built a number of the locks in the Rideau Canal. He also built a fine mansion for himself that is now known as Rideau Hall, the residence of the governor-general.

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