Cracks on Severn River Bridge don't worry state Situation bears more monitoring, other expert says

September 16, 1990|By Robert Lee | Robert Lee,Staff writer

Only three years after the state spent $18 million expanding it to six lanes, thousands of cracks have appeared on the surface of the Route 50 Severn River Bridge.

The cracks, which also appear on Jersey barricades along both east- and westbound lanes of the bridge, don't pose any danger to the structural integrity and don't warrant any immediate action, said Jeff Kolberg, chief of the state's bridge inspection division. But the cracks, many of which are not visible to the casual driver, may cause the deck to wear prematurely, as trapped moisture expands and contracts during freeze/thaw cycles.

Kolberg said deck cracking problems are common on bridge improvement or bridge expansion projects, because concrete doesn't set as well around vibrations.

Academic engineers agreed that the cracks don't put the bridge in any immediate danger, but encouraged inspectors to monitor the progress of the cracks carefully, as possible warnings of a larger problem in the way the bridge vibrates or handles stress.

"It's true, hairline cracks are normal, but those cracks would not fairly be described as hairline," said Andrew Douglass, a mechanical engineer specializing in crack analysis at Johns Hopkins University. "Bits of concrete are coming out of the crack."

Douglass said the cracks could be serious if they were to grow in frequency, thereby loosening the deck and aggravating the problem.

Kolberg, however, discounted Douglas' worst-case scenario, saying his inspectors thought the problem looked like a simple concrete-curing problem.

"Concrete cracks, that's a fact of life, especially when the concrete sets on a vibrating surface next to traffic and on top of already hardened concrete," Kolberg said.

"Ideally you would build a bridge and then send traffic across it," he added, "but we can't do it that way; we have to maintain traffic. Studies have been done by the federal Highway Administration showing that the cracking does not sacrifice anything for the safety of the bridge."

A study was conducted in the fall of 1989 on similar cracks on five different bridges expanded between 1986 and 1988 along Interstate 83, the Jones Falls Expressway, in Baltimore.

That study group, led by David Schelling of the University of Maryland, concluded the severity of the cracks was "low to none," and that repairs "would result in significant reduction in rideability and aesthetics and loss of pavement grooves."

The group recommended against any repairs.

Harry McCullough, chief of the Interstate Division of Baltimore City, who oversaw the expansion of the JFX, said the cracks were smaller than those he saw in pictures of the Route 50 bridge. He speculated that was probably because the U.S. 50 bridge, which is longer and higher than most of the bridges along the JFX, is subject to more severe vibrations.

Douglas said a key issue to determining whether the problem is serious is whether the cracks have reached their zenith, as would be the case if the concrete had been set improperly.

James Joyce, a mechanical engineer at the Naval Academy, agreed.

"Just like when you're building a house and the drywall starts cracking," he said, "you can say that's OK, just replace the drywall. But that doesn't solve your problem if there's something wrong with the building that's causing the cracks."

Kolberg said the cracks' progress would be monitored as a part of routine inspections the department conducts every other year on the state's bridges. He said he saw no-need for additional inspections, and expressed confidence the bridge's major structural supports - eight huge steel girders running the length of the structure - were in no danger whatsoever.

Earle S. Freedman, the State Highway Administration's deputy chief in charge of bridge development and Kolberg's supervisor, said the department has begun successfully experimenting with new concrete curing procedures, to minimize cracking on replacement decks.

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