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At the site, Hoeppner talked to construction workers who survived the fall. They had been doing repair work but expressed concern to him that the bridge had been wobbling several days before it collapsed. Every layer of concrete the workers removed, the bridge would wobble even more, they told Hoeppner.

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Executive Summary:
If bridge replacement is significantly delayed, the bridge should be re-decked. The design of main river spans do not allow for deck widening. Any re-decking contract should also include a complete re-painting of the superstructure elimination of the hinge joint in span #2, and reconfiguration of the deck drainage system.

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The contract required Progressive to repair the bridge deck, replace the concrete surface and expansion joints and work on the anti-icing system, said Minnesota Department of Transportation spokesman Kevin Gutknecht.

Company officials said the crew was preparing to pour a 2-inch layer of concrete when the span gave way.

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COOKSVILLE, Md. - The main protection against collapsing bridges in America are the eyes and ears of inspectors like Jody Ferris, who on Friday was checking a repaired weld on a 34-year-old bridge with some pretty low-tech tools: flashlight, hammer, ruler and camera.

Experience is what counts, said Ferris' boss, Joe Miller of the Maryland Department or Transportation. "Nothing is better than the human element."

Many in the industry disagree, and a federal test of bridge inspectors gives them reason for concern. On one bridge, a fifth of the inspectors missed serious problems.

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Originally posted by glassman:
i wonder if there's thermal imaging or sonic imaging that can detect "defects" i know that Xrays can, but they are not very safe...

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Q. What other testing methods do you use?


A. We take a magnetized yoke and put it on either side of where we think the crack is, and that polarizes one side from the other. You sprinkle metal filings right on the surface. Magnetizing will polarize those metal filings, and they'll line up. Where you have a crack, there will be a discontinuity. You'll see a nice crack where there aren't any metal filings. That will also detect a minor subsurface crack.

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After setting an ambitious goal in the late 1990s of keeping 65 percent of Minnesota's bridges in good condition, state transportation officials retreated from the target as they fell behind in their efforts to reach it.
The top bridge engineer in the Minnesota Department of Transportation (MnDOT) said the agency began discussing lowering the goal in 2003 and later dropped it to 55 percent, a reversal that came as MnDOT faced mounting financial challenges.

Though MnDOT officials said the goal was revised to reflect what other states were doing, and not to lower any safety standards, some legislators said the change is one more sign of how a beleaguered department was forced to align its expectations with dwindling financial resources.

As of last year, MnDOT was falling short of even its lowered goal.

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The men and women whose job was to ensure the safety of Bridge 9340 were meeting once again. Just after noon on Dec. 6, they filed into a conference room in Roseville to divvy up the final prep work for a dangerous steel reinforcement project high above the Mississippi River.

A senior engineer was going to pull property records in order to contact landowners beneath the bridge. Detours were coming for West River Road. The Coast Guard was about to get heaps of paperwork on what tasks would be done from the river channel. Truck drivers would soon learn of pending weight restrictions.

It appeared that the most studied bridge in Minnesota, the focus of worrisome inspection reports for a decade, was finally going to have its most glaring weaknesses fixed.

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Originally posted by glassman:
corosion...

my experience in the Navy ( and several of my own boats) is that what you see is (like an iceberg) only a small portion...

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I found a picture of one of the "gusset plates" you were talking about earlier....



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One is never completely useless. One can always serve as a bad example.

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ST. PAUL, Minn. - Pounded and strained by heavy traffic and weakened by missing bolts and cracking steel, the failed interstate bridge over the Mississippi River also faced a less obvious enemy: pigeons.

Inspectors began documenting the buildup of pigeon dung on the span near downtown Minneapolis two decades ago. Experts say the corrosive guano deposited all over the Interstate 35W span's framework helped the steel beams rust faster.

Although investigators have yet to identify the cause of the bridge's Aug. 1 collapse, which killed at least 13 people and injured about 100, the pigeon problem is one of many factors that dogged the structure.

"There is a coating of pigeon dung on steel with nest and heavy buildup on the inside hollow box sections," inspectors wrote in a 1987-1989 report.

In 1996, screens were installed over openings in the bridge's beams to keep pigeons from nesting there, but that didn't prevent the building of droppings elsewhere.

Pigeon droppings contain ammonia and acids, said chemist Neal Langerman, an officer with the health and safety division of the American Chemical Society. If the dung isn't washed away, it dries out and turns into a concentrated salt. When water gets in and combines with the salt and ammonia, it creates small electrochemical reactions that rust the steel underneath.

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WEST MEMPHIS, Ark. - Officials shut down a major Mississippi River bridge Monday after a pier under a small approach span settled nearly 4 inches during the night in a construction zone.

The approach span for the Interstate 40 bridge was still supported by other piers, so the most motorists might have noticed would have been a slight dip, said Randy Ort, a spokesman for the Arkansas Highway and Transportation Department.

He said the entire 1.5-mile-long bridge into downtown Memphis will remain closed until sometime Tuesday. Traffic over the river was diverted to the nearby I-55 bridge.

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According to a 2001 MnDOT report, the agency chose a relatively expensive de-icing chemical called CF7, a liquid potassium acetate manufactured by Cryotech, a division of San Diego-based General Atomics. The agency said it selected the chemical, in part, "because it is safer for structural steel and reinforcing steel embedded in concrete" and is readily biodegradable.

"Also the fluid contains no nitrogen or chlorides," the report said. "Therefore, CF7 is considered much safer for the environment than glycol, urea, or chloride-based anti-icing chemicals."

MnDOT discovered that the chemical reacted with galvanized metals, however, when some was spilled on a grate. Cryotech issued a technical bulletin in 2005 saying a slow reaction can occur when potassium acetate and zinc come into prolonged contact. Zinc is used to galvanize steel.

In an update, the company said the reaction was not an issue during normal use. It cited a MnDOT project looking into whether the anti-icing chemical was creating advanced deterioration on the I-35W bridge. It concluded that the galvanization on the bridge components was thick enough.

Cryotech could not be reached for comment on Wednesday.

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In testimony before Congress on Wednesday, the state's top bridge engineer indicated that fatigue does not appear to be the cause of the Interstate 35W bridge collapse.

The Minnesota Department of Transportation has been under scrutiny since revelations that several months before the Aug. 1 collapse - which killed 13 people - the agency opted for further inspections rather than a bridge repair initially recommended by engineering consultants.

"Up to this time, fatigue has not been identified as an issue," said Dan Dorgan, bridge engineer for MnDOT, cautioning that the National Transportation Safety Board still needs to complete its investigation.

The bridge was the subject of two exhaustive studies, both of which looked into hairline cracks that inspectors found in steel on its approach spans. Video of the collapse shows the center span over the Mississippi River fell first, not the approach spans.

Dorgan and several others, including U.S. Department of Transportation Secretary Mary Peters and Minneapolis Mayor R.T. Rybak, testified during a daylong hearing on Capitol Hill led by U.S. Rep. Jim Oberstar, D-Minn.

Oberstar is proposing a 5-cents-per-gallon increase in the federal gas tax to improve bridges across the country, where one in eight are deemed "structurally deficient." Peters said a gas tax hike wasn't necessary and that instead, Congress could limit federal earmarks, which she said consume federal transportation dollars.

That led to several clashes with Oberstar and other Democratic members of the House Transportation and Infrastructure Committee.
"It would be immoral to have this bridge collapse and do nothing about it," Oberstar said at the conclusion of the hearing, after Peters had left.

But the proposal found support from the U.S. Chamber of Commerce, the American Trucking Association and several others, including senior transportation officials in other states.

The strongest testimony came from Donald Kaniewski, legislative and political affairs director for the National Construction Alliance, a coalition of trade unions that included the union representing a crew working on a deck repair job the day of the collapse. One worker was the 13th victim recovered from the wreckage.

Kaniewski said the workers should have been replacing the bridge, not repairing it.

"We believe they were doing the wrong job," he said.

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Water runoff from the I-35W bridge created a 4-foot-by-6-foot hole in the ground near one of the bridge's concrete support piers weeks before the bridge collapsed, a Minnesota Department of Transportation spokesman said Tuesday.
Crews filled the hole with cement and the washout didn't affect the bridge's structural integrity, MnDOT spokesman Kevin Gutknecht said.

"The pier didn't sink. The pier is mounted on bedrock," Gutknecht said. "Nothing eroded under the pier."

He described the site of the erosion as being 50 to 60 feet up the hill and away from the base of Pier 5, which stood on the west bank of the Mississippi River. When the I-35W bridge collapsed on Aug. 1, the deck first gave way above Pier 5 at the southern end of the bridge's steel truss spans.

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MINNEAPOLIS -- The law firm of Schwebel, Goetz and Sieben filed a lawsuit Friday against the Minnesota Department of Transportation seeking documents related to the 35W bridge collapse. The suit is an attempt to force MnDOT to comply with the Minnesota Government Data Practices Act.

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These photos are being used to document the recovery efforts and in the ongoing investigation of the collapse.

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ST. PAUL — Minnesota’s transportation emergency management director was fired Friday in part because she remained on the East Coast 10 days after an Aug. 1 Minneapolis bridge collapse.

Minnesota Department of Transportation officials fired Sonia Morphew Pitt, 43, of Red Wing after an investigation found she abused work-related travel privileges and did not return to the Twin Cities as her agency responded to the Interstate 35W bridge disaster.

According to her termination letter, Pitt attended an emergency management conference in Boston July 31-Aug. 4, but extended the trip with stops in Washington, D.C., before and after the conference

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The connectors, called gusset plates, were roughly half the 1-inch thickness they should have been because of a design error, NTSB Chairman Mark Rosenker said. Investigators found 16 fractured gusset plates from the bridge's center span.

"It is the undersizing of the design which we believe is the critical factor here. It is the critical factor that began the process of this collapse. That's what failed," Rosenker said at a news conference.

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Rosenker noted that structural weight had been added to the Minneapolis bridge in two major renovations, in the 1970s and 1990s.

"When they added the weight they didn't realize they were bringing the margins of safety down to where they didn't exist anymore," he said.

Rosenker said that construction materials on the bridge the day it collapsed, which were part of a resurfacing project, added about 300 tons and were on the same side where failure of the bridge began.

Asked if the construction was the tipping point, Rosenker said, "I'm not ruling it in, and I'm not ruling it out." That will be left to the final report to determine, he said.

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