When a hurricane tracks up the Atlantic coast to batter Charleston, S.C., the wind may whip up the seas or rattle the storm shutters on the beach houses, but the Arthur Ravenel Jr. Bridge should remain unflappable. The bridge is being designed to withstand wind gusts in excess of 300 mph.
The other natural hazard Charleston has to worry about is an earthquake. The city was almost completely leveled by an earthquake in 1886, so the new bridge has to be able to withstand a good shake without falling down.
"The seismic criteria was developed by a group of experts from around the world, including some from California," Bobby Clair, the project manager for the Ravenel Bridge construction and the director of engineering and special projects at the South Carolina Department of Transportation, told Roads & Bridges. "They developed the seismic criteria for this bridge that requires that it be designed for a 3,400-year-return event. The bridge basically will withstand without total failure an event up to about 7.3 or 7.4 on the Richter scale."
South Carolina broke ground on July 2, 2001, on the bridge, which will be the longest cable-stayed span in the Northern Hemisphere, at least until the New Mississippi River Bridge is completed in St. Louis. The Ravenel Bridge, with a price tag of $531 million, will replace two existing bridges linking Charleston and Mount Pleasant, S.C., over the Cooper River.
The bridge is the culmination of a couple of decades of political and financial wrangling spearheaded by Arthur Ravenel Jr., a South Carolina state senator who helped secure the funding for the bridge.
A large part of the funding—$215 million—is coming in the form of a federal loan under the Transportation Infrastructure Finance and Innovation Act of 1998. The rest is being made up of money from the SCDOT, Charleston County, the State Infrastructure Bank and the South Carolina State Ports Authority.
Built to take a licking
The deck of the bridge will ride almost 200 ft above the water level, while the two diamond-shaped towers will soar to a height of 570 ft. The bridge will have a total length of 13,200 ft, with interchanges at each end. The main span will be 1,546 ft long. The bridge will carry four lanes of traffic each way, separated by a center barrier. Each lane will be 12 ft wide, with 4-ft shoulders inside and outside and a 12-ft bicycle and pedestrian path. The bridge deck will be more than 129 ft wide overall.
Palmetto Bridge Constructors, a consortium of 15 companies led by Skanska USA Civil’s Tidewater Skanska division, Virginia Beach, Va., is responsible for designing and building the bridge. Skanska’s partner on the project is Flatiron Structures Co., a unit of HBG. Parsons Brinckerhoff is leading the design team.
The foundation for the Ravenel Bridge will consist of drilled shafts 10 ft in diam. sunk 210 ft into the earth. Tests of the local conditions determined that the design would protect against the effects of soil liquefaction caused by an earthquake.
Because the bridge is a design-build project, the design may evolve during construction, but the structure will most likely be cast-in-place concrete.
CCTV cameras will transmit pictures of the bridge to SCDOT’s monitoring stations in Charleston and Columbia and to the local traffic stations and police departments in Charleston and Mount Pleasant, said Clair.
The Ravenel Bridge is scheduled to be opened in July 2007, but Clair said it might actually be completed 10 to 12 months earlier.
The groundbreaking ceremony included 15 speakers, including South Carolina Gov. James Hodges, U.S. Sen. Ernest Hollings and various other officials. They all breathed a sigh of relief that they finally had their bridge started.
More information is available on the Ravenel Bridge website (www.ravenelbridge.org), which like the bridge is under construction, and from the South Carolina DOT (www.dot.state.sc.us).
