Falling Down

The I-35W Bridge Collapse Exposes Dangerous Deficiencies in the Nation's Transportation Infrastructure.

Inspectors, for example, will close lanes and walk the roadway looking for potholes. They will examine the steel beams supporting the deck for cracks and corrosion. They look at the concrete abutments holding it all up for cracks or settling. They check that bearings the bridge rests on are aligned correctly and painted.

For hard-to-reach places, crews employ a "snooper truck," equipped with a long arm and bucket that swings a crew member over the side for an up-close inspection.

If they find something wrong, they can bring in diagnostic equipment such as ultrasound to get a better look at the problem.

Small cracks in steel can be easily repaired by, paradoxically, drilling small holes at either end of the fracture, which stops the crack from spreading. But repair crews have to be careful to drill at the end of the crack, which often can't be seen by the naked eye. To find it, they can use a dye penetrant test, in which they coat the surface with a red dye, wipe it off, and cover it again with white dye. The red coloring will seep through the white dye along the crack and reveal itself.

Bridge workers can also outline a crack by the magnetic particle method. They use magnets to create a magnetic field in the steel beam, then sprinkle the area with a powder of iron filings, which will outline any cracks present.

Bridge inspections are conducted at least every two years (the I-35W bridge was looked at annually). Special fracture-critical inspections were conducted every four years, but the federal government recently recommended two-year intervals.

When the inspection is over, crews rate the deck, superstructure, and supports on a scale of 0 to 9, with 9 being the safest. The I-35W bridge's superstructure was rated 4, meaning inspectors found it in poor condition. —Matt Smith

MURKY WATERS

Will the I-35W bridge collapse have serious environmental ramifications? The massive heap of concrete, steel, vehicles, and lord knows what else would seem to pose a danger to the well being of the Mississippi River.

Environmental concerns initially focused on three railroad cars that were crushed by the collapsed bridge. There could have been serious ecological harm if those cars had been carrying a highly toxic substance, such as benzine. But as it turned out one of the cars contained plastic pellets, while another held plastic powder. The third was empty.

"There was a little bit of spillage," says Sam Brungardt, public information officer for the Minnesota Pollution Control Agency. "Nothing that would pose an environmental or a health threat."

Another possible environmental issue stems from gasoline seeping into the water from crushed vehicles. But oil pollution appears to have been surprisingly limited. "There was a little bit of oil but that dissipated very rapidly," says Brungardt. "We never really found pockets of oil."

A concern going forward will be air quality. As workers untangle and remove the debris, the MPCA is worried about what types of particulate matter will begin circulating in the air. The agency has done preliminary testing near the site of the bridge collapse to establish baseline levels of lead, asbestos, silicates, and other potentially dangerous materials. "Those are all things that are known to affect health if they are breathed in," Brungardt says.

But overall it doesn't appear that the bridge collapse will have any serious, long-term impact on the health of the Mississippi River. "One could imagine scenarios where much worse cargo could have been on that bridge," says Whitney Clark, executive director of Friends of the Mississippi river. "That does not appear to have happened."—Paul Demko

SUGAR BEAT

The Star Tribune and Pioneer Press newsrooms recently received an unexpected box of junk food, courtesy of The Roanoke Times. The spoils include spicy pork rinds, moon pies, Virginia peanuts, Hostess cupcakes, and Dove bars. "There's also one very out-of-place looking can of lima beans," Pi Press metro reporter Frederick Melo reports via email.

This sweet tradition was apparently started by The Oklahoman newspaper, which learned the stresses of covering a major breaking news story after the Oklahoma City bombing of 1995. Last April, after Seng Hui-Cho killed 32 people at Virginia Tech, the Roanoke Times received a large box of artery clogging edibles from their counterparts in Oklahoma. "It was just like a big hug," recalls Carole Tarrant, editor of the Roanoke daily.

The loot is apparently equally appreciated by newsroom staffers in the Twin Cities, many of whom have been logging long hours since the I-35W bridge collapsed last Wednesday evening. "I'm in fat boy heaven," reports Melo.

Tarrant says she only asks that the Pi Press and Strib reporters reciprocate the gesture down the road. "Tell 'em to pass it on," says Tarrant. "That's my only request." —Paul Demko

BRIDGE DESIGN FOR DUMMIES

The collapse of the I-35W bridge has suddenly shoved the relatively obscure science of bridge engineering and inspecting into the spotlight. Here's what you need to know:

What does "structurally deficient" mean? It's a federal designation based on annual or biannual inspections. The feds use a nine-point scale to rank the structural soundness of bridges in three different areas—the deck (which is what you drive on), the superstructure, and the substructure. If a bridge ranks four or lower in any of these areas, it makes the list.

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