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WORLD / America
Minn. bridge problems uncovered in 1990
(AP)
Updated: 2007-08-03 08:40
MINNEAPOLIS -- Minnesota officials were warned as early as 1990 that the
bridge that plummeted into the Mississippi River was "structurally
deficient," yet they relied on a strategy of patchwork fixes and
stepped-up inspections.
"We thought we had done all we could," state bridge engineer Dan Dorgan
told reporters not far from the mangled remains of the span. "Obviously
something went terribly wrong."
Questions about the cause of the collapse and whether it could have been
prevented arose Thursday as authorities shifted from rescue efforts to a
grim recovery operation, searching for bodies that may be hidden beneath
the river's swirling currents.
The official death count from Wednesday's rush-hour collapse stood at
four, with another 79 injuries. But police said the death count would
surely grow because bodies had been spotted in the water and as many as
30 people were still reported missing.
In 1990, the federal government gave the I-35W bridge a rating of
"structurally deficient," citing significant corrosion in its bearings.
The bridge is one of 77,000 bridges in that category nationwide, 1,160 in
Minnesota alone.
The designation means some portions of the bridge needed to be scheduled
for repair or replacement, and it was on a schedule for inspection every
two years.
Dorgan said the bearings could not have been repaired without jacking up
the entire deck of the bridge. Because the bearings were not sliding,
inspectors concluded the corrosion was not a major issue.
During the 1990s, later inspections found fatigue cracks and corrosion in
the steel around the bridge's joints. Those problems were repaired.
Starting in 1993, the state said, the bridge was inspected annually
instead of every other year.
A 2005 federal inspection also rated the bridge structurally deficient,
giving it a 50 on scale of 100 for structural stability.
White House press secretary Tony Snow said while the inspection didn't
indicate the bridge was at risk of failing, "If an inspection report
identifies deficiencies, the state is responsible for taking corrective
actions."
Gov. Tim Pawlenty responded Thursday by ordering an immediate inspection
of all bridges in the state with similar designs, but said the state was
never warned that the bridge needed to be closed or immediately repaired.
"There was a view that the bridge was ultimately and eventually going to
need to be replaced," he said. "But it appears from the information that
we have available that a timeline for that was not immediate or imminent,
but more in the future."
Federal officials alerted states to immediately inspect all bridges
similar to the one that collapsed.
The eight-lane Interstate 35W bridge was Minnesota's busiest bridge,
carrying 141,000 vehicles a day. It was in the midst of mostly repaving
repairs when it buckled during the evening rush hour. Dozens of cars
plummeted more than 60 feet into the Mississippi River, some falling on
top one of another. A school bus sat on the angled concrete.
Engineers wondered whether heavy traffic might have contributed to the
collapse. Studies of the bridge have raised concern about cracks caused
by metal fatigue.
"I think everybody is looking at fatigue right now, fatigue due to heavy
traffic," said Kent Harries, an assistant professor of civil and
environmental engineering in the University of Pittsburgh's School of
Engineering. "This is an interstate bridge that sees a lot of truck
traffic."
After a study raised concern about cracks, the state was given two
alternatives: Add steel plates to reinforce critical parts or conduct a
thorough inspection of certain areas to see if there were additional
cracks. They chose the inspection route, beginning that examination in
May.
Dorgan said officials considered the cracks on parts of the bridge to be
stable and not expanding.
When conducting inspections, Dorgan said, inspectors get within an arm's
length of various components of a bridge. If they spot cracks, that leads
to more hands-on testing to determine the depth and extent of the
fissures.
The collapsed bridge's last full inspection was completed June 15, 2006.
The report shows previous inspectors' notations of fatigue cracks in the
spans approaching the river, including one 4 feet long that was
reinforced with bolted plates. A 1993 entry noted 3,000 feet of cracks in
the surface of the bridge; they were later sealed.
That inspection and one a year earlier raised no immediate concerns about
the bridge, which wasn't a candidate for replacement until 2020.
In a 2001 report from the University of Minnesota's Department of Civil
Engineering, inspectors found some girders had become distorted.
Engineers also saw evidence of fatigue on trusses and said the bridge
might collapse if part of the truss gave way under the eight-lane freeway.
"A bridge of that vintage you always have to be concerned about that,"
said Richard Sause, director of the Advanced Technology for Large
Structural Systems Center at Lehigh University. "In a steel bridge of
that age, sure you'd be concerned about those kind of things and be
diligent about looking after it. And it seems like they were."
It takes time for a fatigue crack to develop, but a crack can then expand
rapidly to become a fracture, said James Garrett, co-director of the
Center for Sensed Critical Infrastructure Research at Carnegie Mellon
University. "If you get a crack that goes undetected it would be
something that appears to happen more rapidly."
At the scene, about 15 divers and a dozen boats were in the water, but
the search was proceeding slowly because of strong currents and low
visibility. By mid-afternoon, they had located four submerged cars
besides the dozen or so visible from the surface.
"We have a number of vehicles that are underneath big pieces of concrete,
and we do know we have some people in those vehicles," Police Chief Tim
Dolan said. "We know we do have more casualties at the scene."
Meanwhile, relatives who couldn't find their loved ones at hospitals
gathered in a hotel ballroom for any news, hoping for the best.
Ronald Engebretsen, 57, was searching for his wife, Sherry. His daughter
last heard from her when she left work Wednesday in downtown Minneapolis.
Her cell phone has picked up with voice mail ever since.
"We are left with the hope that there is a Jane Doe in a hospital
somewhere that's her." Sherry Engebretsen was later confirmed as one of
the dead.
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