Beginning this Saturday night at 10 p.m., northbound traffic on Interstate 81 will have to take Exit 23 at Mosheim, cross U.S. Highway 11E, and take the on-ramp to continue northward.

Enlarged crews from General Constructors, of Mt. Juliet, Tenn., will be working through the night of Nov. 14-15 to repair two small "metal fatigue cracks" in the beams underneath the interstate bridge, said Paul Degges, chief engineer with the Tennessee Department of Transportation.

By 10 a.m. on Sunday, normal northbound traffic is expected to be restored on Interstate 81, Degges said. "We hope to get done faster than this," he said.

Traffic must be diverted from the bridge because vibrations from traffic passing overhead would make it impossible to properly perform repairs involving welding, Degges said.

A week later, on the night of Nov. 20, southbound traffic will have the same diversion, again while crews work through the night to repair a single crack in one beam under the southbound bridge, Degges said.

Each of the bridges is supported by five beams, Degges said, so even if one beam were to fail, the "redundant" beams would be expected to support the bridge.

Deggs and others said TDOT scheduled a press conference underneath the bridge on Tuesday to emphasize the agency's belief that there is no danger of the bridge failing.

In both 12-hour repair periods, law enforcement officers will be on hand to direct traffic, and every effort will be made to alert motorists ahead of time.

"Traffic will still be able to flow," Degges said. Motorists will be able to travel in both directions on 11E and on I-81, and will be able to use all on-ramps and off-ramps.

However, he said, because of the difficulty of routing traffic from one off-ramp to the opposite on-ramp, priority will be given to traffic on Interstate 81.

Degges added that anyone traveling through the interchange on U.S. 11E at Exit 23 should expect delays during the 12-hour period each weekend.

Julie Oaks, a TDOT public information officer, and Travis Brickey, a TDOT spokesperson, said law enforcement from Greene County and the Tennessee Highway Patrol will be present at the bridge and in the vicinity while the repairs are being made.

Obviously, priority will have to be given to traffic on the interstate highway while the repairs are being made, Oaks and Brickey said.

Persons who normally use either I-81 or U.S. Highway 11E to travel to church on Sunday will need to either consider an alternate route or plan to be delayed, Brickey said.

Greene County Sheriff Steve Burns said TDOT asked him to make three cruisers available to help direct traffic, and he plans to do so.

Alerting motorists will be complicated somewhat by the fact that many who will be traveling the highway will already have been diverted onto I-81 due to a rock slide that has closed Interstate 40 just east of the North Carolina line, said TDOT's Brickey.

The I-40 detour will not be altered during the repairs.

Degges said the fact that I-81 is already carrying extra traffic is "unfortunate," but was not a big enough factor, by itself, to postpone the repairs.

Degges said the contractor had been rehabilitating the beams as part of a $1.2 million project that includes bridge deck repairs, painting and installation of a system to detect trucks that are too high to pass under the bridge and stop them before they damage it.

In the process, the contractor identified two cracks in beams under the northbound bridge, and one under the southbound bridge.

"TDOT believes the cracks developed some time after the last bridge inspection was conducted in July 2008," according to a press release.

It is estimated the cost of the additional repairs will be $79,271.

Crews will use a welding technique called "full penetration welding," in which molten metal is created during the process. The molten metal "penetrates the entire bridge beam" and eliminates the cracks.

Before traffic is allowed to resume crossing the bridge, the weld will be x-rayed to make sure it was performed correctly, Degges said.

Wayne Seger, manager of TDOT's bridge inspection and repair office, said additional testing was to begin today.

He said the repair to the southbound bridge would involve removing a section smaller than one square foot from the vertical "web" of the beam, and welding a steel plate back to replace it.
Degges said the bridges at Exit 23 were built in 1968.

Bridges normally have "about a 50-year life expectancy, but it's not unusual to get 100 years of service out of a bridge." He noted that several bridges in Knoxville are 100 years old.

Federal law calls for bridge inspections on a 24-month cycle, he said.

Rehabilitation work, such as the work in which the "metal fatigue cracks" were discovered, are part of an ongoing effort to extend bridge life, Degges said.