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|Publication Number: Date: September/October 2003|
Issue No: Vol. 67 No. 2
Date: September/October 2003
When the bridge to a popular Florida island developed a severe crack, the county DOT sprang into action. Here's how the bridge reopened ahead of schedule.
What if you're faced with closing down a bridge that is the only link between an island community and the mainland, in the middle of the busy tourist season? How would you prepare for the possibility of medical emergencies, so you don't leave residents stranded while the bridge is closed for repairs? Naturally the repair calls for an effective plan, community involvement, and an even faster rebuild.
|The middle bridge (above) and the drawbridge (below) are two of the three spans that form part of the causeway from Punta Rassa on the mainland to Sanibel Island.|
Sanibel Island on the Gulf Coast of Florida, near Fort Myers and 2 hours' drive south of Tampa, is a popular vacation destination for winter tourists. The 23-kilometer (14-mile)-long island is home to about 6,000 permanent residents. Sanibel and adjacent Captiva Island have miles of white sand beaches beloved by shell collectors. On one shore of Sanibel is the J.N. "Ding" Darling National Wildlife Refuge, a destination for bird watchers. The only way to reach these locations from the mainland is by a causeway connected by three bridges—or by boat.
On January 6, 2003—at the peak of the tourist season—the Lee County Department of Transportation (DOT) discovered a severe crack in a beam that supports the causeway's middle bridge. After a temporary emergency repair to stabilize the bridge and protect public safety, the county DOT worked feverishly for 2 weeks preparing to replace part of the superstructure of the aging span.
The story made the evening news and the front page of the local newspaper day after day, as island residents and businesses prepared to be cut off from the mainland. Parents sent their children to motels in Fort Myers so that they would not miss school if the bridge failed to reopen on schedule. A helicopter stood by in case of medical emergencies, and officials urged people using medications to ask their doctors to extend their prescriptions. The phone company stationed personnel on the island for emergency repairs in case of a broken line. Trash pickups were rescheduled.
During the bridge shutdown, all went smoothly. Island restaurants ferried their employees over by boat. The United Parcel Service used a boat to deliver thousands of packages. Sanibel hotels offered specials to tourists so that they could extend their stays. And the hotels and restaurants staged "make-lemonade-out-of-lemons" parties.
A Model of Teamwork
Island residents made positive comments about the Lee County DOT when the bridge reopened hours ahead of schedule. The Fort Myers newspaper, The News-Press, carried a full-page story under a banner headline and ran a companion human-interest piece titled, "Islanders, Visitors Go with the Flow." The experience was like going back in time with many residents riding bicycles on parts of the causeway that were still open. Several residents joked that the bridge should close more often. However, based on numerous comments, one of the main emotions that people felt was relief when the bridge reopened early.
What the local media did not report was that the DOT planned it that way.
"We picked a timeframe that we knew that we could make," says Paul Wingard, P.E., deputy director of the Lee County DOT. "If we shorted ourselves [by releasing a completion date that could not be met], we could've stranded tourists, so we gave ourselves some extra time."
|Many of the businesses on the island, including this shopping plaza, blend into the island's tropical landscape.|
In fact, the Lee County DOT planned for several contingencies, as did the Lee County Board of Commissioners, who granted emergency powers to their chairman so that he could act on decisions quickly. Similarly, the Sanibel-Captiva Islands Chamber of Commerce coordinated a transportation plan for an anticipated 2,000 tourists and held a massive public information campaign so visitors and essential personnel would know where to park on the mainland and what to expect. Best of all, the residents and visitors rose to the occasion and took the inconvenience with exceptionally good humor.
The upshot? The story of Sanibel Island's bridge repair is a model success story—with a couple of lessons learned, of course.
Historical PerspectiveThe county built the causeway to Sanibel Island in 1961-1962 and opened it in 1963, paying for the construction with a bond issue. In this model, revenues from tolls repay the bond and build up a replacement fund.
Starting from the mainland, the 5-kilometer (3-mile) causeway consists of bridge A (a drawbridge); then a spoil island, built with sand dredged from San Carlos Bay; bridge B (the one that developed the severe crack); another spoil island; and finally bridge C, which connects to Sanibel Island. The two-lane causeway and bridges consist of two 4-meter (14-foot) lanes with no shoulders.
|On this map, the drawbridge, or "bascule," is Structure A. The middle bridge (Structure B) is the one that required emergency repairs.|
Because of the bridge's location, the saltwater environment is conducive to corrosion. Each of the two fixed-span bridges is constructed of four precast concrete beams with concrete decks, founded on pile caps supported by piles driven into the sea bottom. The spans were designed for lighter trucks than those typically found on highways today; however, nothing was wrong with that. The legal design loads used in the late 1950s were smaller than today's design loads (H15 versus HS20 or HS25, for example).
Since 1971, Federal mandates have required bridges in all States to be inspected at least once every 2 years. In the mid- to late 1980s, the Florida DOT initiated an annual bridge inspection program for drawbridges and continued inspections every 2 years for fixed spans. About that time, the Lee County engineers found some deterioration in the Sanibel bridges and proposed to replace them with a single high-span structure reaching all the way from the mainland to the island. The manmade spoil islands were to be removed because they appeared to be blocking some of the flow from San Carlos Bay as it flushes into the Gulf of Mexico. But voters vetoed the proposal on aesthetic grounds.
In the early 1990s, Lee County and the City of Sanibel conducted additional inspections, all of which pointed to accelerating deterioration. Major repairs were done in 1991 and again in 1996.
But the deterioration continued, so the county started another campaign to replace or repair the bridges. The DOT conducted public outreach to determine citizen preferences and hired an engineering company to prepare a preliminary report. The conclusions of that report were that span A (the drawbridge) could be repaired and last another 20 years, span B needed to be replaced immediately, and span C should be replaced but could last another 8-10 years with some fairly extensive repair work. The report also concluded that the spoil islands could remain because water-flow studies showed no major blockages.
The county board of commissioners approved that report in June 2001. Because the causeway is located over navigable waters, the U.S. Coast Guard is the lead permitting agency. The Coast Guard gave preliminary approval in fall 2001, and the U.S. Fish and Wildlife Service provided its consent the following fall. The Lee County DOT moved forward with design. The only remaining question was whether to replace span C at the same time as span B to gain the economies of scale or to replace it down the road. By the end of 2002, the DOT was pursuing a design contract for the replacement of B and C, plus repair of the drawbridge. "Everything was going smoothly," says Wingard.
The Crack Appears
Then the first week of January 2003 arrived. During a routine inspection, a county bridge crew spotted what appeared to be an unusual crack in one of the interior beams of the middle bridge (B). The Florida DOT had conducted its inspection during the spring of 2002, and the county crew had inspected in December 2002. Neither inspection had revealed any evidence of failure. When the county crew went back 3 weeks later, however, to follow up with some routine maintenance, they were alarmed and called Wingard by radio from their boat.
"My first reaction was that it was probably minor surface cracking," says Wingard, "but I quickly realized that it was much more significant than that."
|Scott Gilbertson, transportation director for Lee County, was able to drive his fist through the worst crack.|
Wingard and the county bridge engineer Betsy Rowan visited the site and found that the crack ran from the bottom flange immediately above the seawall all the way to the top of the beam. Theoretically, two beams carry the load of the traffic in one direction, and two for the other direction. Observing the beam for almost an hour, Wingard and Rowan decided that the crack was "very significant" because of the way the beam was deflecting when a heavy load passed overhead.
By the next day, the Lee County DOT had reinforced the beam with temporary steel posts at the location of the crack and also placed posts to shore up the other beams. A structural engineering company determined that the post-tensioning of the beam was failing and recommended replacement of the bridge's damaged 15-meter (48-foot) center section. For the replacement, they suggested using steel girders and steel open-grate decking to avoid the week-long curing needed for concrete.
Working Around the Clock
Lee County DOT brought in the steel girders in advance, and the Florida DOT supplied steel decking. Meanwhile, county officials began their planning—incorporating aspects of Sanibel's hurricane evacuation plan into their emergency response strategy. The city posted updates on its Web site and set up a tourist hotline, while the newspaper ran Q-and-A stories to prepare residents and visitors.
Some tourists decided to end their vacations early and go home before the shutdown. But most elected to stay. For those scheduled to leave during the shutdown, island businesses would pay for sightseeing boats to ferry them from Sanibel to Fort Myers, where buses would shuttle them to the airport. At the airport, volunteers would staff an information booth coordinated by the Lee County Visitors and Convention Bureau. Buses would convey arriving tourists to the ferries, where they would be met by buses and taxis and taken to their hotels.
Meanwhile, residents and civic organizations made their plans as well. Even Sanibel's wildlife rehabilitation center made contingency plans, deciding to continue accepting injured animals from the mainland. A boat staffed by a volunteer would make the pickups.
|All of the new beams are in place, and workers are welding the steel grate.|
|This car has just crossed the repaired middle bridge of the Sanibel causeway.|
The DOT elected to start the shutdown at 10 p.m. on Sunday, January 19, as the next day was Martin Luther King Day and schools would be closed. The shutdown was expected to last 32 hours, with the bridge slated to reopen at 6 a.m. on Tuesday.
As The News-Press reported, it went "like a military exercise" despite a chilly night. Law enforcement barricaded the site to keep the curious at a safe distance while the contractor sawed the bridge deck into four sections. A crane lifted the detached deck, rail, and beam sections, each weighing up to 22,700 kilograms (50,000 pounds). The workers removed the first section from the pile caps by 3 a.m. Monday and by 5 a.m. had removed the other three.
After clearing the rubble, the contractor began replacing the superstructure with the preassembled steel girders and grate. On Monday, a winter cold front kept temperatures below 70 degrees (chilly for a winter day in southern Florida) as the workers welded the steel deck grate into place. By 7 p.m., Scott Gilbertson, transportation director for Lee County, announced that the bridge would reopen by midnight Monday instead of 6 a.m. on Tuesday—only 26 hours after it closed.
And, in fact, traffic did start crossing the bridge again 6 hours ahead of schedule.
Examining the Pieces
"When we saw-cut the girder to see what was going on inside," says Wingard, "the prestressing strands and reinforcing steel looked as good as new in a number of places—like the day the bridge was poured. But directly over the seawall, some strands were corroded all the way through."
The concrete was porous and punky with surfaces weakened by chemical attack. Wingard says that past repairs at that location may have trapped chloride ions in the concrete. "Sandblasting and removing loose concrete and then patching over with gunite, and maybe not getting a real good bond," he says, "may have accelerated the deterioration. The beam disintegrated at the point of the crack as we handled it. But 10 or 15 feet [3 or 4.5 meters] away, the
concrete and steel looked good."
The conclusion: As waves lapped against the seawall, the beam had been splashed with saltwater over and over and then dried, only to become wet again during the next storm.
"The crumbling of the concrete raised concerns about the other spans," says Wingard. A complete inspection of the other bridges found additional cracking, although not as severe, and signs of possible internal deterioration. So the DOT reduced speed limits on the bridges to 22 kilometers (20 miles) per hour and imposed weight limits of 15 metric tons (17 tons) for single-unit trucks,
22 metric tons (24 tons) for combination trucks. Special arrangements are made for heavier vehicles to creep across at night one at a time at 15 kph (10 mph).
The county DOT rethought its original assumptions. "Several engineering companies took a look and said that we need to replace B now, no time to waste," says Wingard. "So we are moving forward on a much accelerated schedule."
The designer and contractor are on board, and the DOT is using a construction-management arrangement so that as soon as the piles are ready, the contractor can begin driving them, and as soon as the substructure is designed, the contractor can begin building it. The county hopes to start driving piles for B and C by late 2003.
The county board of commissioners declared an emergency to enable the DOT to accelerate the approval of the final Federal permits. In addition, the county DOT and the University of Michigan ran load tests with strain gauges on the drawbridge to determine deflection and load-carrying capacity. The outcome was a recommendation that the county should continue the current weight and speed restrictions on Structure B and replace the drawbridge in lieu of rehabilitation.
The State and county plan to step up their inspections to once every
6 months, and the county will do a quick inspection once every month with crew members in a boat spending a couple of days visually looking for changes from the previous inspection. "One of the lessons learned," says Wingard, "is that structures in a saltwater environment like this need to be checked more frequently than the standard."
He adds, "Another is that we may need to take a harder look at how we're doing repairs. Some of those previous repairs where they chipped away concrete, sandblasted the steel, and then patched over it may not have been a good fix because they may have trapped some moisture inside and increased corrosion." Using sacrificial anodes so that they corrode instead of the reinforcing steel might work out in this type of situation.
Wingard adds that another lesson is to get the critical structural elements up out of the splash zone. The beam that failed was only about 2.4 meters (8 feet) from the water line. The Florida DOT's new standard is that the bottom of the beams has to be a minimum of 3.7 meters (12 feet) above high-water level. "If we go out during a storm and see a lot of water splashing up from the seawall onto the new beams," says Wingard, "we may have to do something else to enhance the protection, like putting on a concrete sealer."
In the meantime, the costs of the repairs have risen to $552,000 to date.And the newspaper and television stations continue to follow the Sanibel Island bridge story closely.
Norah Davis is a contract writer for FHWA and editor of PUBLIC ROADS magazine.
For more information, contact Paul Wingard at 239-479-8545.