Inside looking out

Access ports to provide entry into bridge girders near Nashville

By Candy McCampbell

Highway Department engineers in Tennessee will no longer be on the outside looking in.

A bridge being built as part of a new $31 million, 2.8-mi. section of Nashville's Vietnam Veterans Boulevard by Rogers Group Inc. of Nashville will have access ports in its steel cap girders so engineers can crawl inside for inspections.

The bridge's steel beams tie into the girders, which in turn rest on the concrete columns.

Vietnam Veterans Boulevard, or State Road 386, runs from Interstate 65 at Nashville's northern edge, bypasses Hendersonville and will end near Gallatin. The current construction segment runs from Saundersville Road to Station Camp Creek Road.

"The contract completion date is November 2006, but we're scheduling it to finish in October 2006," said Todd Nash, project manager for Rogers Group. Clearing started in November 2003.

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Gerald Guinn, executive vice president of steel erector Sentry Steel Co. Inc. of Hendersonville, said the cap girders weigh about 39 tons each and reach as long as 28 ft.

The 780-ft.-long steel girder bridge is the largest of six in the boulevard extension and sits on concrete-filled steel, 6-ft.-wide metal cans sunk 12 to 38 ft. deep. The cans support cap girders that are bolted to steel bridge girders, which will carry traffic over a railroad track.

Nearby, a 740-ft.-long steel girder bridge stands on poured-in-place concrete piers that support span lengths of 279 ft., 224 ft. and 236 ft., Guinn said. The remaining bridges are made of precast concrete beams over poured-in-place concrete substructures, the longest stretching 265 ft.

D.W. "Red" Binkley, Sentry's general superintendent, said the steel bridges will require the largest bolts ever used on a Sentry project, measuring 13.5 in. long and 1 in. diameter.

"We're using 29,000 (of the) 1-in. bolts," he said

Concrete caps must be positioned exactly right because fabricator Vincennes Steel Corp. of Vincennes, Ind., has pre-assembled the steel girders at a radius.

"They put the bridges together, 200 ft. to 300 ft. at a time, to the right pitch and elevation," Guinn said.

The bridge girders are made of high-strength steel that develops a thin layer of rust to self-protect the girders from additional corrosion.

Laydown space is scarce.

"We take delivery as needed, and they go up within a day of delivery," Nash said.

The bridge is topped with panels of metal decking laid by crews from Gilley Construction Co. of Manchester, Tenn.

Gilley is also placing and tying 800 tons of epoxy-coated rebar on this job, said Vicki Gilley, company president.

Guinn said all the bridges have concrete decks averaging 9 in. thick. The decks have more than 6,800 cu. yds. of Class D concrete and the substructure has more than 5,000 cu. yd. of Class A concrete.

"We got a lot of paving done in January," Guinn said. "We had some good weather and took advantage of that."

The project also has three box culverts, two for existing streams and one to allow access for vehicles and cattle on a farm that is bisected by the highway.

Work started on the bridges sooner than planned because the site work was done quickly, Nash said.

"The subcontractor that did the grading, Wright Brothers, did an excellent job in moving quickly, and allowed us to start the bridges quicker," he added.

"This job consisted mainly of rock fill. With them being able to get that volume of earth moved, it put us (ahead) several months."

The project required moving a total of 377,874 cu. yds. of material, 223,037 cu. yds. of which was rock. Some of the rock came from a cut in a hillside and nothing had to be hauled offsite.

"This is an all-rock job," said Tom Whitsitt, vice president, chief engineer and estimator at Wright Brothers Construction Co. Inc., of Charleston, Tenn. "There are no seasons in an all-rock job, so that's one of the things that helped" the site work finished early.

The road runs through open land, so Wright could use off-road equipment instead of highway trucks to haul the rock.

Another break came when the Tennessee Department of Transportation allowed Rogers to limit traffic to one lane for bridge erection, Nash said.

"The specs allowed us to close on weekends, but it would have been 10 to 14 weeks," Nash added. "We asked TDOT to have one-lane traffic for 7 to 10 days, which cut down on the amount of time."

The mayors of Hendersonville and Gallatin also were "very receptive" to the more limited highway closing, he said.

CSX Railroad keeps a flagman on duty whenever road crews are out so he can alert them of approaching trains and alert engineers of the construction.

Utilities were taken care of early on, with Nashville Gas Co. relocating gas lines and White House Utility District moving water lines.

There is little drainage involved, because the shoulders are designed for runoff, Nash said. Just under 6,000 ft. of concrete pipe, ranging from 18 in. to 48 in., are being used.

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For more information about the project, go to: http://www.tdot.state.tn.us/