For a bridge in Florida, the mortal enemies are saltwater, vibrations and time. Over decades, salt can seep through a bridge's concrete skin and corrode its steel skeleton like a cancer. Rusted rebar can swell to six times its original size, making the surrounding concrete buckle and flake. Waves can scour away the earth around bridge pilings. A lot of bridges around the Tampa Bay area were designed to last roughly 50 years. Today a lot of them are 50 years old — or older. Bridge inspectors keep a wary eye on them. "They're all reaching the end of their life span at the same time," said Pinellas County bridge engineer Tony Horrnik.
With a damaged bridge, the question comes down to: How long do we keep repairing it before we replace it entirely? What's more cost-effective in the long run?
Tight budgets don't make those decisions any easier, Horrnik said.
On a recent morning, Horrnik was on a boat beneath a bridge that was about to be demolished in Tarpon Springs' Fred Howard Park. He pointed out cracks and decay on the bridge's underside. The park's popular causeway and beach had just closed for a whole year so a new bridge can be built.
"People will see the topside and say, 'Why replace this bridge, especially during this time when budgets are so limited?' " Horrnik said. "We wouldn't replace it unless we absolutely had to."
Each bridge is ranked on a sufficiency scale of 1 to 100. When its rating dips below 50, the government starts thinking about replacing it. There are 20 such spans in the Tampa Bay area. Some are being replaced soon, and some aren't.
"A low sufficiency rating doesn't necessarily mean the bridge is unsafe," said Pepe Garcia, the state Department of Transportation's facilities engineer for west-central Florida.
The rating takes into account a span's age, design and upkeep. It reflects the bridge's current condition compared to how it would be if it were built to today's standards, Garcia said. The lower the number, the more a bridge needs to be brought up to date. If it falls to 20, the span must be replaced.
A look at some local bridges:
John's Pass: Strong currents have undermined the old bridge's pilings, but a new southbound span may open as soon as this week. It will handle all traffic until a new northbound span is done in 2010.
Belleair beach Causeway: This major route to the gulf beaches is nearly 60 years old and its concrete has been crumbling away, exposing steel. More than once, it's been closed for emergency repairs. A new $72.2-million bridge rising 75 feet above the water should be finished by spring 2010.
Welch Causeway: Leading from the Bay Pines area to Madeira Beach on (no kidding) State Road 666, this bridge scores a 45.8. But Garcia says it's structurally safe, and the state has taken steps to protect its pilings from erosion.
Paul Buchman Highway Bridge: This span over the Hillsborough River on State Road 39 near Zephyrhills still has timber pilings. It will be replaced beginning in fall 2009.
Old Tampa bridges: Crossing the Hillsborough River, the bridges on Cass and Platt streets and Columbus Drive are so old, they've been designated as historic landmarks. They date to the 1920s and have repeatedly been repaired. For now, they're safe for cars to cross.
For how long? Nobody knows.
Mike Brassfield can be reached at email@example.com or (727) 445-4160.