Better Bridges

Tennessee rehabs major bridge

We closely studied the alternatives and decided that this option would be economically feasible rather than adding a totally new structure. We were further able to effect a significant taxpayer dollar cost savings by using our own existing in-house design and engineering forces,” says Tennessee’s DOT Assistant Area Regional Manager, Ken Flynn.

The state estimate to rehabilitate the existing structure was approximately $26.5 million compared to $34.9 million to design and construct a new bridge. The Jones Brothers Construction Company of Mt. Juliet, Tennessee was awarded the low-bid contract of $25,676,938.32 to widen the U.S. Route 27-SR 29 Olgiati Bridge.

Workers will extend the bridge from four existing lanes (two in each direction, with no shoulders) to six lanes (three in each direction, with full shoulders). Additional future widening is also provided for. The contract calls for improvements to be made to the existing 4th Street and Manufacturers Road Interchange.

The challenges

Britton Bridge was faced with two distinct construction challenges. The first was to add to and widen the existing 10 land-based piers to support the new bridge configuration. This was the conventional part of the project. The second phase was to extend the caps of the four massive water piers by adding twin steel cantilever beams and shoulder beams to each pier without disturbing them and their foundations. Engineering tests indicated that the existing water piers would support the built-up steel plate girders required to support the deck widening.

The eight cantilever beams (two for each water pier) were among the longest and heaviest single pieces of steel fabricated for the job. They were 141.6-feet long and weighed approximately 218,000 pounds each. These were shipped to the job by rail where they were transferred to barges on the river and floated into position. Two large, barge-mounted Link-Belt crawler cranes, a 250-ton capacity LS-278H and a 150-ton capacity LS-518, were used to lift the big cantilever beams into position.

“If you have the correct amount of lifting capacity on a job like this, no one will ever remember your name. But, if you don’t, you will go down in history. Everyone will know your name. You will be infamous in a heartbeat. You’ll either tip a crane over and into the water or you’ll drop a massive steel girder or both. I hope in my career that I never get famous that way,” says Jerry Britton, chief manager of Britton Bridge, LLC.

“We work very hard to achieve a safe, balanced lifting approach on every job that we do. That’s just one of the many reasons for our fleet of a dozen or more Link-Belt machines. I’d like to have two of the new 250-ton capacity LS-278H heavy-lift cranes here, but such is not the case, we only own one of them. However, we do a lot of our own engineering on a project and we knew that we could do all the work here with it and an older 150-ton capacity Link-Belt LS-518.”

For the water work involving hanging the steel, each Link-Belt crane was mounted on a separate floating barge. The LS-278H was rigged with 160 feet of boom with a six-part line, load block and a whip line. The LS-518 had a 150-foot boom, a six-part load line, and a whip line. Because of strict Coast Guard channel closing restrictions, Britton Bridge crews normally worked shifts from 7 a.m. until midnight several days a week when hanging the transverse steel girders.

The steel erection, according to Jerry Britton, was facilitated by the use of several Terex manlift units, also working from barges. In the past, skilled ironworkers would ride the load up, bolt it together, and walk across a 4-inch-wide flange 100 feet in the air to bolt the other end of the beam in place.

Change was brought about through new safety standards, technology, and a shortage of the old time ironworkers. While no less productive and skilled a craftsman, today’s high ironworker rides a man-basket to work, is tied off to it with a safety harness, and often uses an air impact wrench instead of the traditional spud wrench.

“Today the work is no less dangerous, but our guys go home at the end of their shift to their wives and families better paid and with all their fingers and toes intact. They are safer and more productive, if a little less dramatic in their occupation,” says Britton, himself an old-school bridge builder.

The 11,340,744 pounds of structural steel was manufactured, fabricated, and painted by Carolina Steel Corporation of Montgomery, Alabama. It was shipped to the bridge job site by truck and rail. Some of the longest and heaviest transverse girders were offloaded directly from the existing bridge deck after temporarily closing down one lane of traffic. They were then lifted into position by the barge mounted Link-Belt LS-278H crane. No steel erection was ever begun until all steel was on hand for a full day’s work.

Because of the size and weight of some steel girders, they were fabricated in sections and assembled in place using both barge-mounted Link-Belt cranes. A case in point was the haunch girders. They were erected one piece at a time, each weighing about 102,000 pounds, being roughly 10-feet deep and 137-feet long. When bolted together they would have been too tall for over-the-road transport and too heavy to erect as a single unit. Using both Link-Belt cranes, Britton Bridge was able to easily achieve a balanced approach.

The over-the-water erection was done after requiring the contractor to first extend the existing land pier foundations by adding to them, then form and pour the new piers, and, finally, widen the existing pier caps.

The required 35,020 feet of new 12-inch steel H-beam foundation support pile averaged between 30- and 60-feet long each. They were driven to bearing or refusal depending upon location, with a Link-Belt LS-138H crane and a Delmag 3032 pile hammer. Soil mechanics engineering borings showed a mixed bag of common riverbank to be driven through.

Poured-in-place pile caps, pier foundations, and land columns were added and the varying height, 6- by 6-foot reinforced columns were then formed and poured. New pier caps were formed and poured and new structural steel was added for both the main bridge widening and for interchange improvements.

Complete state-contractor co-ordination and balanced machinery seemed to be the keys in keeping this project running smoothly.

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Reprinted from Better Roads Magazine
August 2001

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