Gov. Blagojevich on Thursday ordered state inspectors to examine all bridges considered to be critical as Illinois officials sought to assess the safety of its bridge network in the wake of the deadly collapse in Minneapolis.
But even as the governor took aggressive measures, structural engineers and bridge safety experts cautioned that there was no cause for panic — Illinois bridges are inspected regularly and tragedies such as the one in Minnesota are isolated incidents, often involving many factors.
“American bridges simply don’t collapse of their own volition,” said David Schulz, director of the Infrastructure Technology Institute at Northwestern University. “It’s almost always a chain of low-probability events coming together. It takes a lot to bring these down.
“I don’t worry about bridges,” he said. “When we look at spectacular bridge failures, I think what you’re going to find is that somebody did something that affected the bridge and that it wasn’t the structure or the bridge itself.”
Blagojevich acknowledged that Illinois regularly and vigorously inspects its bridges and that he undertook this measure as a precaution. He was among a slew of governors across the country who ordered new inspections. By Thursday evening, the federal government had alerted states to inspect spans similar to the Minneapolis bridge.
Illinois compiles a list of priority bridges based on a rating scale that uses various measures to assess safety and deterioration. The 1-100 scale is used to prioritize replacement or repair of bridges. The higher the rating, the better the condition. A rating of 80 or less means the bridge probably needs some rehabilitation. A rating of 50 or less means the bridge may need to be replaced.
At least three spans on the Skyway were rated structurally deficient, with ratings in the low 70s.
But engineers stress that when a bridge is structurally deficient, that does not mean it is unsafe for travel. It simply is no longer able to carry the load size for which it was designed. In response to a structurally deficient bridge, engineers will assess the damage and then determine new weight limits.
“A structurally deficient bridge is still perfectly safe to use for years and years and years, provided the limits are not overly stressed,” Schulz said.
But engineers also are looking at a highly trafficked bridge on the Bishop Ford Expressway near 130th Street because it has been deemed structurally deficient in past inspections, Kollias said.
Slowdowns through the Dan Ryan Expressway construction zone have put additional vehicles on the Bishop Ford bridge recently, she added.
But overall, “there is not a reason for people to be worried about driving in their vehicles,” Kollias said. “We have done our inspections.”
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BUSIEST STRUCTURALLY DEFICIENT BRIDGES
BY COUNTY
A I-94 at Washington Street
B Ill. 176 at Kishwaukee River
C Main Street at Fox River
D I-90/94 between Stewart Avenue and 28th Place
E 75th Street at West Branch DuPage River
F Ill. 53 at Lily Cache Creek
[ SOURCE: US DEPARTMENT OF TRANSPORTATION ]
