JANUARY 2008 ISSUE
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KEYSER FILE
Bridge Brigade is No Place
for Complacency
BY TOM KEYSER
Freelance Columnist
Two inspectors say the province’s network of bridges is in good shape. That’s reassuring, but APEGGA members and government must remain vigilant — and aware that much of our infrastructure isn’t exactly brand new
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SAFE CROSSINGS |
By definition, Alberta’s bridges include immense steel spans across rivers and wooden catwalks over lazy creeks, everyday highway grade separations and minor crossings of culverts.
They’re the responsibility of counties, municipal districts, cities and railroads, as well as the provincial Ministry of Infrastructure and Transport.
And they’re all subject to two-to-five-year rotating inspections, which is reassuring. But the situation calls for vigilance. The difficulty finding qualified engineers to hire, funding shortfalls, the growing infrastructure deficit, even climate change — all these could eventually threaten the high safety standards we enjoy.
In the wake of major collapses in Minneapolis and Laval, bridge and overpass safety has emerged as a front-burner issue. And two of Alberta’s senior bridge inspectors tend to agree: the long-term enemy isn’t timber rot, metal fatigue or corrosion.
It’s complacency.
Eyes and More
Arnold Assenheimer, P.Eng., and Paul Carter, P.Eng., both assign reasonably high marks for strength and stability to as many as 19,000 bridge-type structures around the province.
Mr. Assenheimer manages the Sherwood Park office of MPA Engineering, and he has seen just about everything to do with bridge quality in 28 years of inspections. His team specializes in smaller structures, performing the visual assessments known as level one inspections.
The job demands that inspectors keep their eyes peeled for signs of deterioration and weakness in timber and pre-cast superstructures, cast-in-place concrete and steel. Sometimes, an evaluation that goes deeper than eye-balling is necessary.
“For example, you may spot timber caps that look like they’re rotting but you can’t verify it with the naked eye,” Mr. Assenheimer says. “Then we may recommend a level two inspection. Another engineering team comes out with ladders and equipment and does more extensive testing to confirm interior problems.”
Not long ago, Mr. Assenheimer conducted 24 visual inspections for Smoky Lake County, about an hour northeast of Edmonton. After spotting irregularities in one timber substructure that betrayed telltale signs of rot, he immediately called the county and advised a lane closure.
“I would say any serious problems that we do detect are dealt with pretty quickly, whether they’re smaller bridges on country roads or larger ones on primary highways,” he says.
The Next Level
Paul Carter, bridge rehabilitation manager for CH2M HILL in Edmonton, has made a specialty of the more sophisticated level two inspections, relying on space-age techniques such as copper sulphate electrode and ultrasonic testing.
In 2007, his team ran flat out, conducting almost 500 level one inspections, plus 120 level two inspections on provincial bridges and nine more for the City of Calgary. In addition, Mr. Carter’s group and a partner firm ran 40-plus ultrasonic inspections on steel bridges.
“We identify problems and pass the information back to the owners. The parties responsible for maintaining the bridge are pretty prompt about responding.”
The inspectors routinely rely on fascinating tools. High-frequency sound waves enable them to detect minor cracks and fatigue in the tension members of older steel truss bridges. Techniques employing copper sulphate electrodes help engineers to gauge the extent of corrosion in structural concrete members by measuring electrical potentials generated by the corrosion process.
Some county councils have more bridges than they
have funding to maintain. You don’t really need a road every mile and councils
are starting to realize this.
-Arnold Assenheimer, P.Eng.
But high tech or not, the work needs qualified people. Naturally, both CH2M HILL and MPA share the staffing challenges common to every engineering firm in the province.
“We struggle the same as everybody else,” confirms Mr. Carter. “You have to be fairly aggressive and make sure you’re hiring the best possible people.”
Mr. Assenheimer tries to train two new inspectors a year. “I bring them into the field with me but it takes two years to get them to the point that I’m confident in what they’re doing.”
Maintaining Safety
Detecting problems is only part of the bridge safety story, though.
Systematic programs of bridge washing, deck sealing and curb sealing represent
the best kind of preventive maintenance, keeping chlorides from seeping into
the superstructure.
Although he sees no reason to worry about funding for major bridge maintenance, Mr. Assenheimer has found that smaller jurisdictions can’t always keep up. His suggestion: close non-essential roads in remote rural locales.
“Some county councils have more bridges than they have funding to maintain. You don’t really need a road every mile and councils are starting to realize this.”
Climate change can’t help either. Regional weather extremes are already a major factor in bridge wear. Alberta is notorious for temperature fluctuations and rapid freeze-thaw cycles.
“But other jurisdictions pour much more road salt on their bridges than we do,” counters Mr. Assenheimer. “I’ve been shocked to travel down east and look over their structures. You see corroded steel and salt corrosion penetrating the concrete.”
Age is another concern. As Mr. Carter points out, an enormous number of bridges were erected shortly after the Second World War (the bridge construction boom started about 1950 and carried on until about 1970). They were certainly built to last — but there are limits.
And some bridges still in use are even older.
“Consider Edmonton’s High Level Bridge,” notes Mr. Carter. “It was designed for trains and still has a tremendous load-bearing capacity. But soon it will be 100 years old.”