Rebuilding a community link: 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

Public Roads, Sept-Oct, 2003 by Norah Davis

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 ha 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."

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 ha one direction, and two tot 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.