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Published: Monday, 8/6/2007

High-tech tools to aid investigation in Minneapolis bridge collapse

FROM THE BLADE'S WIRE SERVICES

MINNEAPOLIS A helicopter with a camera similar to those used in Hollywood movies soon will peer into the wreckage of last week s I-35W bridge collapse.

Laser-guided surveying equipment has helped produce an in-depth map of the debris. Software re-creating the disaster on a computer screen may even be able to pinpoint the exact piece of bridge that gave way.

Investigators trying to determine the cause of the disaster are armed with a powerful technological arsenal that will enable them to get answers much quicker than in previous eras, when crews literally had to put the pieces of a fallen bridge back together.

Computers and modeling techniques are just light years from what was available 40 years ago, said Ted Galambos, a professor emeritus of structural engineering at the University of Minnesota and an expert in the stability of structural steel.

Now we can have an idea and we can test that on a computer in a few hours.

Progressive Contractors Inc. began the $2.4 million project to repair sections of the heavily traveled highway in June. Progressive s workers pounded away at the road surface with jackhammers, cut loose pavement with industrial-strength saws, and mixed and poured concrete.

The bridge collapsed Wednesday toward the end of a shift, taking Progressive s 18-person crew with it. One worker is feared dead. At least five people were killed and about 100 injured. Eight people remain missing.

For now, the construction project is only one item on a long list of possible causes that also includes aging steel, rotting welds, vibrations from adjacent train tracks, and even the corrosive effects of bird droppings.

But the company s work on the structure has become a crucial early part of the investigation by the National Transportation Safety Board.

Yesterday, the NTSB said it had interviewed company officials and workers and was analyzing construction and maintenance documents.

Employees of Progressive of St. Michael, Minn., have helped investigators map out the locations of its equipment, vehicles and materials at the time of the accident, and how much each piece weighed.

The company s work at the time was concentrated on a section of bridge over the river toward the southern end, NTSB Chairman Mark Rosenker said.

Mr. Rosenker called the interviews quite informative, but declined to say what they revealed.

Investigators also plan to watch frame-by-frame enhancements of video of the collapsing bridge. In addition, the FBI used laser-guided surveying equipment to complete a detailed 3-D map of the wreckage, and quickly provided the data to the lead investigation agency, the National Transportation Safety Board.

Nineteen NTSB investigators from around the country are in Minneapolis, working out of trailers, hotels, and command posts. W. Gene Corley, senior vice president of CTL Group, an engineering firm who has helped investigate bridge collapses, predicted the NTSB should have a pretty good idea within a few weeks of the cause.

The NTSB says the bridge will not have to be fully reassembled, largely because of all the technology they have.

Meanwhile, across the Twin Cities, in Spanish, Greek, and English, the prayers rose up yesterday.

Prayers of peace for grieving families. Prayers of strength for those still searching the Mississippi River. And prayers of gratitude from those who were spared.

At Holy Rosary Church in Minneapolis, the faithful thanked God for the angels who rescued 50 terrified children from a school bus when the span collapsed.

Some of those children sat in the first few rows, then laid bouquets of flowers at a candlelit shrine to the Virgin Mary.

The thing I always think about is if we were seconds ahead or seconds behind, we could ve been under the bridge or in the water. It makes me feel lucky I m still alive, said Elfego Vences, Jr., 16, who was on the bus with his 13-year-old brother and 12-year-old sister.

The Rev. Jim Barnett said that the church considers the survival of its children a miracle, and that the service was designed in part to help them heal.

At St. Olaf Catholic Church in downtown Minneapolis, parishioners observed a moment of silence for both the victims and the recovery workers, who continued to search the dangerous debris-filled water for bodies.

The Rev. Mark Pavlik said the bridge has been a daily part of life for many of the several hundred worshippers, a modern convenience barely noticed, let alone considered.

Now, it s a sacred spot a grave site, a place in need of prayer.



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