Hurricane season is a perilous time for an uncompleted bridge. Yet, hanging in the Charleston harbor is the state's priciest construction project, the $632 million Cooper River bridge. Half-completed, it can't withstand winds greater than 73 mph. A hurricane could rip it apart.

Engineers and bridge builders, relying on wind tunnel tests, have reinforced the bridge with thousands of pounds of extra weight and taken out a $200 million insurance policy to cover hurricane-related damage.

"It is an anxious time for us," said Bobby Clair, director of special projects with the state Department of Transportation. "If a hurricane hit today, our risk would be minimal. If it hit in late October, our risk of damage to the structure would be much higher. The swaying and twisting would cause us to replace parts of the structure. That would be a major setback."

If the past is an indicator of the future, the bridge may be tested. Twice in the last 15 years, hurricanes that have hit the coast have unleashed winds greater than 73 mph. Hurricane Hugo in 1989 was clocked at 140 mph. The 74-84 mph winds that accompanied Hurricane Floyd as it blew past the city in 1999 also would have challenged the bridge.

Everyone is keeping an eye on this year's forecast.

The National Hurricane Center, which issues a hurricane outlook each May, predicts 12 to 15 tropical storms and six to eight hurricanes. Two to four of the hurricanes are predicted to be major storms, meaning winds greater than 110 mph.

To devise ways to protect the bridge, engineers tested a 4-foot model of the bridge for a year in a wind tunnel.

Laser beams and electronic sensors monitored the swaying, twists and turns as the wind gusts steadily grew from 20 mph to more than 200 mph. Engineers discovered that such high winds can cause the bridge towers to crack and thousand-pound girders to bend or even blow loose.

The tests helped them design the bridge's temporary hurricane tie-down system. The system secures the bridge by providing an additional 8,000 tons of weight to the bottom of the roadway in the harbor, which is supported by 20 cables. Installation of the system began earlier this month.

The cables are on the landward side of each bridge tower, so as not to block marine traffic, Clair said.

Giant blocks of concrete, weighing about 125 tons each, have been placed on a moveable track on the road deck. The tracks allow workers to move the blocks in a weather emergency.

If the tie-downs fail, insurance will pay for the damage.

The state required the bridge's primary contractor, Palmetto Bridge Constructors, to purchase a $200 million builders risk insurance policy on the uncompleted bridge that covers damage caused by winds greater than 73 mph.

For now, the sky is clear and no storms are brewing in the Atlantic. Watchful engineers say they have prepared for the worst, but hope for the best.

"Anytime high winds are predicted during this phase of construction there is cause for concern," Clair said. "Hopefully, the hurricanes will just scoot up the coast like they have for the past couple of years. But we'll just have to wait and see."

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