Bridge Steps Lightly To Spare Cash Crop

By Elaine S. Silver

The Florida panhandle area near the Bryant Patton Bridge is known for its natural beauty and economically important oyster beds. To replace the aging 4-mile-long structure, a first-time design-builder signed on for a $72-million lump-sum contract and threw in a 10-year abutment-to-abutment warranty for good measure.

Located on the Apalachicola Bay in the northeast portion of the Gulf of Mexico, the original Bryant Patton Bridge tied the town of Eastpoint and State Routes 98 and 319 to St. George Island in 1965. The two-lane bridge needed to be replaced because corrosive salt water and the heavy wave action of the bay damaged substructure elements. In addition, inadequate lane widths on the bridge caused significant traffic back-ups and the lack of shoulders raised safety concerns.

In keeping with its lush surroundings, the causeway portion of the bridge also had become a nesting ground for several species of protected birds. The old bridge replaced ferry service to the 29-mile-long island, which has 700 year-round residents and is an attractive summer tourist destination with many rental and vacation homes.

The new bridge is comprised of two parts. The low portion causeway is 3 miles long, mostly on the north or mainland side, with minimum clearance of 14 ft above the water. The high or channel part has 65 ft of vertical clearance from the water. The new prestressed concrete bridge, containing two lanes and two breakdown lanes, was completed in May for the Florida Dept. of Transportation by the design-build team of New Orleans-based Boh Bros. Construction Co. LLC and Jacobs Civil Inc., Tampa.

After hearing about a feasibility study, the team started work on the project in 1997–a year before it was even announced–in order to increase its chances of submitting a winning proposal. Once awarded the job in April 1999, the design-build team completed the project in 1,547 calendar days.

Collaboration between designer and contractor guided the entire project. "The beauty of design-build is that the engineer gets to design towards the strength of a particular contractor," says Steve Zendegui, Jacobs’ senior bridge engineer. In this case, that meant Boh Bros.

The contractor got the project rolling by suggesting that the team use an unusually sized 54-in.-dia pile to satisfy FDOT structural and environmental concerns. The piles, fabricated in 16-ft-long sections, have a 38-in.-dia hollow core and 8-in.-thick walls with holes for steel tendons that are prestressed and grouted. The piles were driven into silt and sand to a lime rock bearing strata. The larger size minimizes disturbances to the bay bottom. The piles support a cap, piers and the roadway. "The overall selection of the pile [size was made] because of the oyster beds," says Ed Scheuermann, Boh Bros.’ office project manager.

	Old and new bridge structures were built near important oyster beds.

The Apalachicola Bay is an aquatic preserve and home to the county’s largest oyster-producing area, a major economic force in the local economy, so the new bridge had to be built with minimum impact on the 10,600 acres of oyster beds. "Oyster harvesting is the largest industry in the area," says Cindy Collins, assistant at the Apalachicola Chamber of Commerce. "Tourism comes in a close second, but Apalachicola Bay produces 90% of Florida’s oysters." According to Mark Berrigan, bureau chief with the division of Aquaculture, Florida Dept. of Agriculture and Consumer Services, oysters bring in "about $20 million to the area."

In order to ensure that the bridge would pass muster from the permitting agencies, "we latched onto using these large piles because Boh had used them before and we also had to design a portion to resist possible barge impact," says Zendegui. "This enabled us to significantly reduce the number of piles used." If a standard 30- in. pile been used, 42 would have been needed in the main channel instead of 15 of the larger piles. "This is a huge savings," says Zendegui. "There are fewer piles so there is less impact on the environment and it was much less time- consuming to drive 15 piles as opposed to 42."

The bridge sits on a total of 650 piles, mostly three per bent, and they range in length from 70 ft to 96 ft, with about 10 ft of each pile visible on the lower approaches. To protect the oysters, the design-build team hired local fishermen to relocate the beds directly under the piles.

Using post-tensioned precast concrete piles speeded the work while the team completed a geotechnical survey of soil conditions. "We could start making pieces immediately and then we could say we need a certain length of pile at a particular bent. So when we got the geotechnical data, the fabricator could join the pile segments together for the appropriate length for each of the substructure components," says Zendegui. "This saved several months at least."

Building the bridge put Boh Bros. at risk. Before settling on the larger pile design, the contractor did a test run. "We cast a sample pile and drove it into a similar-type soil bed in Louisiana," says Al Flettrich, Boh Bros.’ senior project manager, heavy construction. "That way, we could present our findings to FDOT and we knew for ourselves that the pile worked well and we could install it under the specific soil conditions."

Not knowing specific soil conditions also was a risk because FDOT provided data on only 12 borings in the request for technical proposals. The team ended up making over 100 test borings during the project. Fortunately, the soil turned out to be fairly uniform. "In design-bid-build, the piles are unit price and in a lump-sum job, the risk was ours, not knowing what the pile length was going to be" says Flettrich. "One of the other bidders dropped out because of this."

	Precast, post -tensioned concrete sections saved time and money.

The design-build team also took a risk in obtaining all of the necessary permits for the job as it surged ahead. If FDOT builds a job using design-bid-build, it has to obtain all the permits even before the job can be let out to bid, says Doug Cox, Jacobs’ southeast region director of construction. "In contrast, we could submit the plans in pieces to get a jump on the project." The bridge roadway just needed an Environmental Resource Permit, so it made sense to begin with that, says Cox. "Using the design-build contract vehicle means that we can start and complete a bridge in four to five years instead of 10 years," says Steve Benak, construction and materials engineer for FDOT’s District 3.

But one advantage to having permit responsibility was the ability to work directly with utility companies. "This is essential under design-build," says Cox. "We can pay [the utilities] premium time to get the relocation job done or we can elect to have the contractor do it and then you can get it out of the way. If we pay the utility company $30,000 in overtime, we can save $100,000 in time. We are always evaluating as a team how we can add extra value to save the job time and money."

After one verbal agreement, the team ran into a bureaucratic glitch over permits to build compensatory treatment drainage ponds for the stormwater runoff from the bridge roadway. The Florida Dept. of Environmental Protection decided the plan was inadequate because it required relocating an existing sewer line.

"The design-build team had to change the plan for the runoff at its own cost, find a solution and go through the permitting process," says John Kemp, senior project engineer, Parsons Brinckerhoff Construction Services, Eastpoint, which was hired by FDOT for project construction, engineering and inspection. The team then found an alternative site at a special inlet to treat the runoff water. "In the end, everyone benefited," Flettrich says.

	Special grout preserves integrity of steel tendons in concrete piles.

"The largest issue happened when we changed the grout. We wanted it to happen and we paid for it," says FDOT’s Benak. FDOT changed its grouting specifications in mid-project from cement to expensive thixotropic grout. The grout is used to secure the post-tensioned cables in the piles and Scheuermann says the team was a little uncomfortable about using the new grout. "We were using a 54- in. pile that has a pretty good history and then FDOT wanted changes made. But when you are sitting there with the warranty, it is hard to accept them."

Each change potentially could alter the long-term maintenance needs of the bridge, which remains the design-build team’s responsibility. FDOT paid for the change and Boh Bros. sent some of its engineers to a special course to learn to use the new grout.

FDOT wanted the grout change due to bitter experience on two other Florida concrete bridges. The internal post-tensioning strands were breaking on relatively new structures because the old grout would separate and allow salt water to bleed in, creating a corrosive environment. Thixotropic grout stays homogenous and eliminates voids while providing corrosion protection. "The important thing is that it all worked out," says Scheuermann.

The team’s 10-year abutment-to-abutment warranty played a role in design and materials choices. "By providing the warranty, we had to ensure that we had the best materials. We designed some things differently to make sure they exceeded the standards," says Flettrich. "For example, where specifications called for four anchor bolts, the team put in eight."

The bridge now is open and the old one is being dismantled, although a section will remain as a bird-nesting sanctuary. Satisfied with their experience at St George Island, the team now is partnering on a new Interstate 75 bridge over the Peace River. "Using design-build is a lot more fun. The whole process allows the contractor to interact from the beginning to use our best methods and resources to construct a better product with a better price in a shorter time," says Flettrich. "I’d like to see design-build come to Louisiana and Alabama."

The author, a freelance writer, lives in the Hudson River Valley of New York State and reports frequently for Design•Build and other publications.

All photos courtesy of BOH BROS.

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