They designed and built many of the landmark bridges spanning Canadian waters, but when it came to the Champlain Bridge, the father-and-son engineers P.L. and Hugh Pratley lost a big part of the job to a low, exotic bid.

This weekend, roughly 55 years later, work crews are racing to install a "super beam" and save the Champlain Bridge. Hugh Pratley, now 87, shakes his head at the memory of how the "innovative" concrete girder design imported from Europe won over his plan to use traditional steel girders to build much of a 3.4-kilometre crossing over the St. Lawrence River.

"We were ready to go with a similar design to the one my father used 30 years earlier on the Jacques Cartier Bridge, and then this crazy idea came in from France," said Mr. Pratley. "It cost less, so they took the cheapest bid. And now they're paying for it."

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The Champlain Bridge, which is among Canada's busiest and is located in one of the country's key trade corridors, was scheduled to be closed completely early Saturday morning so workers could install a 75-tonne steel girder to shore up a failing concrete beam. The federal bridge authority in Montreal plans to reopen the bridge with the brace until more permanent repairs can take place.

However, the only long-term solution is a new bridge that is expected to cost at least $3-billion.

Montreal is riddled with crumbling infrastructure, but the Champlain is emblematic of problems that have haunted the city for decades: Shoddy construction, neglected upkeep and jurisdictional squabble have contributed to create an emergency situation that could have been avoided.

At the root of the problem was the desire of the Progressive Conservative government under John Diefenbaker to save a buck.

P.L. Pratley came to the project in 1955 with an impressive résumé: His first major job after he arrived in 1905 from Britain was to help investigate the collapse of the Quebec Bridge, where 75 workers died, and to help rebuild it into the world's largest cantilever bridge.

In partnership with engineer C.N. Montserrat, Mr. Pratley would design or oversee the construction of the Jacques Carter and the Île d'Orléans bridges in Quebec, the Thousand Islands, Blue Water and Ambassador bridges in Ontario, and Vancouver's Lions Gate Bridge.

He was working on plans for the Champlain Bridge in 1958 when he died of cancer. His son Hugh, who had just built the Angus L. Macdonald Bridge in Halifax, moved back to Montreal to take over.

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Hugh Pratley had designed the bridge to use steel girders for the entire span when Ottawa decided to break up the project into several contracts and open them up to bidding. Mr. Pratley would build the signature steel 800-metre cantilevered portion of the bridge, and would supervise the overall $30-million project.

But his steel $10.3-million bid for the long, rising approach from the south would lose to the $8.3-million French design, using concrete reinforced by high-tension cables. "The thing is concocted like a piece of knitting, so there's no way you can repair a beam. It's all too tightly tied together," Mr. Pratley said. "But from the point of view of politics, what could they do? It was the lowest bid. It met the basic standards. I wasn't given much of a chance."

An engineering report completed two years ago confirms Mr. Pratley's description, saying the bridge's components are so integrated by the mesh of steel and concrete that replacing a beam is "difficult, if not impossible."

The section of the bridge also lacked design features that would seem basic in Canada. For one, there was initially no conduit to collect and drain away salty concrete-corroding water because ash from burned coal provided grip on icy bridges into the late 1950s. Proper drainage would be added decades later, when the corrosion had already started.

The 2011 report said the bridge was "designed rapidly and constructed with a view to efficiency, economy and speed of construction," a description Mr. Pratley confirms.

Mr. Pratley is watching the rescue operation keenly, from the house where he was born and still lives, a brick Westmount two-storey built by his father. He is confident bridge engineers know what they are doing. "They get criticized so much, but I think they're on the right track," he said.

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Mr. Pratley laughs at the Parti Québécois government's demands that Ottawa provide a billion-dollar addition for light rail and hold a design competition to create a new bridge worthy of international acclaim, all without tolls for drivers.

"Quebec is complaining a lot. They want to have a say, they just don't want to pay a cent," Mr. Pratley said.

How the feds came to own Montreal bridges instead of the province, which owns the road network, is another story. In the 1920s the Board of Harbour Commissioners of Montreal issued a bond (financed by tolls) to build the Harbour Bridge (later renamed the Jacques Cartier).

When the federal government took over major Canadian harbours in the 1930s, it inherited the Jacques Cartier and would later be on the hook for building the Champlain over the federal St. Lawrence Seaway.

Provincial and federal governments have occasionally mused about passing the bridges on to Quebec. Jean Lapierre, a onetime federal Liberal transport minister, describes a 1995 plan to transfer them, along with $450-million for future upkeep, to the PQ government under Jacques Parizeau. With a referendum looming, then prime minister Jean Chrétien got wind of the plan and vetoed it, Mr. Lapierre says.

Now, with a decrepit bridge and a multibillion-dollar replacement needed, the province is unlikely to assume control without a big federal cheque with no strings attached to cover the cost.