The bridge builders no longer need to guess at the stress

September 3, 1999

A project placing sensors in piers of the 13-kilometre Confederation Bridge to learn about structural strains has drawn international interest That oldest of engineering feats, the building of a sound bridge, is going through a technological transformation. A Canadian team has developed a method of embedding into a bridge sensors that will continuously monitor a span's stresses.

The team, headed by an Ottawa-based research institute at Carleton University, is working out of a very large laboratory. Canada's 13-kilometre-long Confederation Bridge is having its countless shakes, bangs and sways recorded.

The technology could mean a renaissance for the field of bridge building. Stress levels need no longer be worked out solely on paper. The data for the two-year-old span that links Prince Edward Island to Canada's mainland now arrives through accurate real-time measurements.

"This is the future direction of civil engineering," says Moe S. Cheung, who is responsible for overseeing the maritime bridge from his office in Ottawa, a time zone away.

"This is one of the new intelligent structures. We are able to take the complete health of a bridge."

The technology can also monitor other stresses. Data from traffic, wind and even a simulated earthquake will all make their way through the sensors built into the cement piers of Confederation Bridge and arrive at the offices of the Ottawa-Carleton Bridge Institute.

Professsor Cheung says this work, for researchers in civil engineering and for the government, which will eventually take over the bridge's maintenance from a private consortium, could not have been possible without the Can$1.6 million (Pounds 700,000) grant from Canada's Natural Sciences and Engineering Research Council.

Commercial sources have also been willing to sink some money into this research. The fact that the span is the longest bridge ever built over ice-covered water makes for some highly marketable data.

One Japanese oil company, with drilling platforms in the Russian Arctic, has been very interested in the stresses caused by the enormous winter ice floes, in this case measuring up to a kilometre long and 20 metres deep.

While several international builders have their eyes on the project data, others wish they could have known about this technology when they were building structures that are now finished. A director of the Anglo-French channel tunnel told him he regrets he was not able to place sensors along its frame.

Professor Cheung may no longer need the iron ring worn by Canadian engineers to symbolise a broken bit of a bridge mishap. The sophisticated telecommunication and computer technology of this project should take engineers beyond educated guesses and crossed fingers. "We are bridging the oldest part of engineering with the newest things offered," said David Lau, the bridge's research team leader.

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