posted 12-14-2000 04:02 PM               

By TOM HELD
Milwaukee Journal Sentinel staff
Update: Dec. 14, 2000

A large section of the Hoan Bridge hung by a veritable steel thread Wednesday night, after two of three support girders cracked and dropped the northbound lanes several feet, authorities said.

While state and local officials pondered the immediate prospect of one or more sections of the bridge collapsing onto Jones Island, residents in Bay View and south shore suburbs pondered months of alternate routes, traffic jams and longer commutes.

The Hoan Bridge, which carries about 35,000 people a day to and from downtown Milwaukee, buckled near its highest point Wednesday morning.

'It could collapse'
As of late Wednesday, a 100- to 200-foot section of the bridge was being supported by one steel girder - one that was found to be cracked six months ago. The section of northbound roadway, about 200 feet south of the bridge crest, is slumping 3 to 5 feet, and there are informal reports that the settling is continuing, officials said.

"Certainly, it could collapse at this point," said Leslie Fafard, director of the state Department of Transportation district based in Waukesha.

"The whole section would fall if the third girder cracked or failed," Fafard said at a midday news conference. "The portion between the ground supports would probably fall."

Fafard said safety concerns were so great that chains were going to be installed to keep curious pedestrians, as well as traffic, off the bridge.

The bridge, which was finished in 1977 at a cost of $47 million, carries about 35,000 vehicles a day. The 2.5-mile expanse connects the southeastern corner of the county to downtown and the main freeway system, and it is a link to the $130 million Lake Parkway, which opened in October 1999.

The bridge will be closed indefinitely; estimates on the time necessary to complete repairs ranged from six months to one year.

While one team analyzes the traffic problems, another team of state officials, local engineering consultants and a national firm with expertise in bridge failures will determine the cause of the failure and how to fix the bridge.

One option is to borrow materials from the Miller Park construction site to help support the bridge structure, officials said. Contractors and engineers will visit the bridge this morning to begin assessing the damage.

Experts theorized Wednesday afternoon that vertical cracks developed quickly in the two failed support beams, causing the deck to bow severely.

Engineering professor Chris Foley, who teaches bridge design at Marquette University, said some force - such as the weight of a heavy truck - in combination with the cold weather probably caused the cracks.

Engineer John Goetter, a manager at the Milwaukee engineering firm of Graef, Anhalt, Schloemer and Associates, said the brittle failures that probably occurred offer little or no warning. Most cracks in the steel girders that support the bridge deck develop slowly and can be monitored, but brittle failure is very rapid, he said.

'So unusual'
Fafard said a combination of factors could have contributed to the failure: temperature extremes; changes in the soil under the bridge supports; and the impact of high winds. All will be studied.

"We are not going to eliminate anything," Fafard said. "This is so extreme, so unusual."

Oddly, the only intact girder on the failing segment is the one that was drawing attention because of cracks discovered in the earlier inspections.

The cracks found six months ago were not considered severe enough to warrant immediate repairs, and a team was sent to review the cracks within the last week, Fafard said.

The cracks in the girder had not changed since the first inspection, and no problems were detected in the other two girders. Cracks of this kind are not unusual in steel bridges, Fafard said.

"There have been cracks for 20 years," Fafard said.

In the fall and winter of 1997, the Infrastructure Technology Institute at Northwestern University conducted field tests to determine whether "thermally driven stresses" caused fatigue cracks discovered in the bridge structure, according to David W. Prine, a researcher at the institute.

Prine was not available for comment Wednesday, but a summary of his research, and other studies he has done on bridges, was available on the Internet.

"The data indicates that thermally induced stresses are probably the primary driving force for the fatigue cracks," Prine said in his summary.

Load limit considered
Officials had been thinking of limiting loads that truckers are allowed to carry on the bridge. The state legal limit is 40,000 pounds, but all bridges are built to handle much more.

Trucks with loads much heavier than 40,000 pounds can use Wisconsin roads legally, however, by obtaining a special permit from the DOT.

Fafard said his department was considering a 160,000-pound limit for the bridge, but he did not know immediately what the limit was at the time of the accident.

"In retrospect, yes, we should have been doing something different, because we've had a failure here this morning," he said.

But there was no reason to believe public safety was at risk earlier, he added.

Engineers from Goetter's firm and from the DOT had been doing more intensive inspections of the bridge because of mounting concerns over cracks, said Dave Schulz, a civil engineer and former Milwaukee County executive.

OTHER BRIDGE FAILURES
• The Walnut St. Bridge in Harrisburg, Pa., collapsed in January 1996 because of flooding.
• The I-5 Arroyo Pasajero Twin Bridges in Coalinga, Calif., collapsed on March 10, 1995, killing seven people.
• A section of the Oakland Bay Bridge in the San Francisco Bay area collapsed on Oct. 17,1989, during the Loma Prieta earthquake.
• The Schoharie Creek Bridge in Schoharie Creek near Amsterdam, N.Y., collapsed on April 5, 1987. Ten people were killed.
• The Mianus River Bridge in Greenwich, Conn., collapsed on June 28, 1983. Three people were killed and three were injured.
• A freighter crashed into the Sunshine Skyway bridge in Tampa Bay on May 9, 1980, killing 35 people.
• The U.S. 35 Silver Bridge between Point Pleasant, W.Va., and Gallipolis, Ohio, fell into the Ohio River at rush hour on Dec. 15, 1967, killing 46 people and injuring nine.
• In Washington state, the Tacoma Narrows Bridge collapsed in high wind on Nov. 7, 1940, because of high winds only four months after opening.

"They were doing the right thing. They were doing a comprehensive inspection," he said of the local officials, but "time ran out."

He also said: "I don't think anyone's a bad guy. I don't think anyone made a bad call. They found a problem, they were working to deal with it."

But Schulz also said the incident bears close inquiry because failures of this type are so rare for a bridge not considered old.

"This is not a random event. This is not an act of God. This is caused by a problem, and the problem has to do with the loading of the structure, the material that was used" to build the bridge "and the way that material was used. There are concerns regarding all those matters," he said.

Foley said it was too soon to determine a cause for the failure, yet he noted that the way girders are welded has changed since the bridge was built. He said he did not believe the incident occurred because of the bridge design, which was done by HNTB Corp.

A spokesman for HNTB in Milwaukee did not return calls seeking comment.

Cost isn't known yet
Fafard said DOT officials were unsure who specifically designed and built the bridge, but they planned to pore over inspection reports to see whether there could have been more warning about the sagging section.

Foley said the bridge could have collapsed entirely later Wednesday, had traffic not been shut down so quickly. But another engineering professor, Kenneth White of New Mexico State University, said that although the bridge clearly is unsafe for traffic, bridges of its type don't collapse quickly.

White, who has 30 years of experience inspecting bridges, said failures such as that on the Hoan are caused by a combination of problems in design, material or workmanship.

Schulz, Foley and White agreed that repairs probably would take at least several months, with Foley saying the time could easily stretch to one year. Schulz said the repairs could take longer because inspectors might find major problems in parts of the bridge other than where the failure occurred Wednesday.

Schulz also raised the possibility that repairs could cost so much that officials might have to consider whether to make them at all.

The cost to fix the bridge won't be known until the engineers' assessment is done, in a couple of weeks or so, Fafard said.

Near South End
The damaged part of the bridge is on the northbound section, about 200 feet south of the large golden arch. The girder in the middle is completely broken, and the one closest to the lake is severely damaged.

The third girder that is supporting the section is the one closest to the southbound lanes, which is actually a separate bridge.

Sheriff's officials and police moved quickly to evacuate businesses and agencies that would have been damaged by the bridge had it collapsed.

Operations at the Port of Milwaukee, which has a number of facilities on Jones Island, underneath the bridge, were halted for several hours Wednesday morning. Officials there were told of problems about 7:30 a.m., Port Director Ken Szallai said.

"It appeared at that point the concern was the bridge might not hold up, and if the structural failure became larger, it would have a domino-like effect, with more sections coming down," he said.