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Some Illinois bridges get visual check

Posted August 02, 2007 11:00 pm

Dana Heupel

State bridge inspectors fanned out across Illinois on Thursday to check spans similar to the one that collapsed in Minneapolis.

About 10 bridges were given visual inspections, said Todd Ahrens, engineer of bridge planning for the Illinois Department of Transportation's Bureau of Bridges and Structures. More will be inspected on state highways and the Illinois Toll Road in coming days.

"The one today is an internal self-assurance kind of thing, and an assurance to the public that we don't have an immediate problem with a structure that's similar to the one that just collapsed," Ahrens said Thursday evening.

"We don't want Illinois motorists and residents who are out on the roadways and crossing bridges in their vehicles to panic," said IDOT spokeswoman Marisa Kollias. "We have a team that is diligently working to double- and triple-check dozens of bridges across the state."

Two downstate bridges are constructed in a comparable manner to the Minneapolis structure, Ahrens said. IDOT policy did not allow him to identify them, he said.

Under federal regulations, bridges are normally inspected every two years, Ahrens said. If potential problems are discovered, they are inspected annually. IDOT is up to date on its inspection schedule, he said.

Unlike the visual inspections Thursday, normal inspections require more sophisticated equipment and more time. A typical bridge inspection might take a couple of hours, he said. A larger one could take three crews several weeks.

Among the highest priorities in the current round of visual inspections, which Gov. Rod Blagojevich ordered in the wake of the Minneapolis collapse, are bridges that are "non-redundant" structures. Sometimes constructed from the 1950s to the 1970s, non-redundant bridges don't have backup construction to carry the load if a portion fails, Ahrens said.

Of the 7,819 bridges on Illinois' state and interstate highways, 211 are non-redundant, Ahrens said, as is the collapsed structure in Minneapolis.

A 2006 Federal Highway Administration study found 9.4 percent of the nearly 26,000 bridges in the state to be "structurally deficient," the same designation given to the Minneapolis span before it collapsed. The highway administration placed that label on nearly 74,000 bridges across the country, or 12.3 percent.

"Structural deficiency does not necessarily imply that a bridge is unsafe," according to a publication by the Federal Highway Administration's Research Center. "It does, however, mean that a structure is unable to carry the vehicle loads or tolerate the speeds that would normally be expected for that particular bridge in its designated system."

Load or speed restrictions are often placed on structurally deficient bridges, and they are often scheduled for major repairs or replacement.

Steel arch bridges, like the one that collapsed in the Twin Cities, are not very common, but there are some in Illinois, said John Harms, senior vice president of Hanson Professional Services, a nationally known engineering firm based in Springfield.

Harms, who has been involved in construction, planning and design of structures such as the Clark Bridge over the Mississippi River at Alton, said several factors could affect the lifespan of a bridge, including maintenance, volume of traffic and heavier loads.

In the Midwest, salt spray during the winter months, as well as cycles of freezing and thawing, can contribute to the deterioration.

"Salt is detrimental to steel. It gets into … the reinforcement bars and cause them to rust," Harms said.

Fatigue often comes into play, as well.

"When you take a piece of wire and bend it back and forth, it eventually breaks," he said, explaining that the same type of thing happens to the steel built into bridges as a result of heavy traffic.

"If any kind of good thing can come out of this, it is that we learn from past mistakes," Ahrens said, noting that there have been no major bridge collapses in Illinois similar in scale to the Minneapolis catastrophe.

Still, Ahrens said the Minneapolis collapse has given even him some pause.

"I'm a lifetime licensed structural engineer. I love bridges, but I have a different outlook on them right now," he said.

Jayette Bolinski of GateHouse News Service contributed to this report. Dana Heupel can be reached at (217) 788-1518 or dana.heupel@sj-r.com.

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