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Inspectors feel weight of bridge's collapse

States dispatch experts. One visits a corroding span in Colorado.

August 06, 2007|Stephanie Simon | Times Staff Writer

PUEBLO, COLO. — There are holes in the steel girders supporting state bridge K-18-R.

Not big holes. The size of a deck of cards, maybe. But the corrosion so alarmed state inspectors on a routine visit Thursday that they asked their supervisor to take a look.

Which is why he's now perched 40 feet above the Arkansas River, bracing his back against the concrete deck of the bridge and his feet against the rust-scarred steel trusses that keep the structure up. Jeff Anderson is tapping the girders with a geologist's pick, listening to each ping and clank for clues about how K-18-R is bearing up. He's waiting for the bridge to talk to him.

"Watch out below!"

A very sizable chunk of corroded steel gives way under Anderson's probing and tumbles down, shattering on the bike path that runs along the river.

Built in 1924 in this modest farm town in south-central Colorado, the bridge is one of about 75,000 nationwide deemed "structurally deficient." Its sufficiency rating stands at 47 on a scale of 100 -- lower, by a few points, than that of Minneapolis' Interstate 35W bridge before it collapsed into the Mississippi River on Wednesday. Anderson's inspection could bump Pueblo's bridge down into the low 20s on that scale.

A heavy truck passes overhead, and K-18-R wheezes like an asthmatic patient: Eeeeh-huh. Eeeeh-huh. The girders tremble under the stress. Just like they're supposed to, Anderson says.

An engineer trained at the University of Colorado at Boulder, he designed bridges for 15 years before joining the state inspection team seven years ago. On this afternoon, he's sweating, filthy and just a bit freaked out by all the spiders -- "I hate spiders," he says, more often than he realizes -- but Anderson is in his element.

The air down here smells of must from the mud-drab river below. Birds flit past, whirling in shafts of sunlight. Dirty white crystals hang like icicles from the underbelly of the bridge deck; they're almost pretty, until Anderson explains that they're formed from mortar leaching out of the concrete, weakening the roadway.

A midweight vehicle rumbles overhead, and K-18-R squeaks insistently, a rusty-tricycle-wheel sound. Then there's a steady, calming whir as a succession of lighter cars whiz by.

Governors in state after state have ordered emergency inspections of thousands of bridges in the wake of the Minnesota collapse.

Some teams will use high-tech equipment: ultrasound to check for cracked bolts or a special dye that can point out stress fractures. Computer modeling helps determine how much weight the bridge can bear. Magnetic particle testing evaluates the strength of welding.

Anderson, 51, prefers to use nothing more sophisticated than binoculars. He brings wading boots and climbing gear to each job (though he shimmied along this bridge with just his bare hands and his Nikes). He likes to get up close to his patients, crawl on and in and under the bridge; he makes his diagnosis by sight and sound.

Or as he puts it: "There's a lot of intuition."

Just now, he's studying the report his inspectors filed the day before. They haven't had time to type it up, so it's just a dust-streaked page scribbled over in red ink. "Section loss W Web. R3 corrosion at abutment plate bearing. R3 R4 Stringer H." Anderson checks each spot. There's corrosion all right, but it's all on the periphery of the steel truss; none of it has even begun to affect the main load-bearing girders.

He can't understand why his inspection team flagged this bridge as critical. An overreaction to the Minneapolis tragedy, he thinks. The unexplained failure there has made some inspectors jumpy, too quick to see potential catastrophe at every weld.

Not that Anderson doesn't recognize the potential for catastrophe.

Colorado's 8,000-plus bridges get visual inspections every two years. Every five years, teams use ultrasound to examine key bolts and pins for cracking. Divers inspect underwater pilings every five years as well.

That regimen is up to federal code. But Anderson knows how much could happen between inspections. A truck could slam into a key support pillar. Joints could freeze up, stiffening girders that are supposed to sway as they absorb stress.

Once, late on a Friday night, he was called out to a bridge -- a major artery through Denver -- because a construction crew working nearby reported an odd slapping noise. It turned out that a connector piece had snapped and one of the two main girders supporting the bridge had broken free. The bridge was closed immediately.

So when he's asked whether the Minneapolis collapse makes him more anxious, Anderson smiles wryly.

"I was already anxious," he says. "I've seen things where, in my opinion, it was only for the grace of God that the bridge didn't go."

Later, he wonders whether he should have said that. He doesn't want to give the impression, he says, that "all the guys in our office are praying every day that the bridges don't fall down."

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