Arthur Ravenel Jr. Bridge

Vertical Access, working with Freyssinet LLC and the South Carolina Department of Transportation, recently completed an investigation of the cables of the longest cable-stayed bridge in North America.  The Arthur Ravenel Jr. Bridge (more popularly known as the Cooper River Bridge) is located between Charleston and Mount Pleasant over the Cooper River in South Carolina.  Completed in 2005, the bridge was designed and built by Parsons Brinckerhoff and Palmetto Bridge Constructors to replace two obsolete bridges: the Grace Memorial Bridge and the Pearman Bridge.  While the Grace Memorial Bridge had narrow lanes and a low vehicle weight limit, both bridges lacked the necessary clearance for large container ships to safely pass underneath.  Prior to the demolition of these outdated bridges, even though Charleston is one of the busiest container seaports in the United States, many large container ships could only pass under the bridges during low tide.  The Arthur Ravenel Jr. Bridge is named after the South Carolina senator who is largely credited with finding the $700 million of funding required for construction.  When Palmetto Bridge Constructors was contracted to work on the bridge, it signed a design-build contract, which allowed construction to begin sooner than with a conventional project schedule.

The bridge deck is supported by 128 wire cables, which hang in a harp-like arrangement from two diamond-shaped towers.  The towers reach 575 feet above the water and are connected by the 1,546-foot long main span.  With a clearance of almost 200 feet over the Cooper River, the Arthur Ravenel Jr. Bridge is designed to allow large container ships to easily reach upstream port terminals.   The base of each tower is shielded from container ship collisions by a large rock island.  Designed to stop a runaway ship before it hits a tower, the islands surround the tower bases with one acre of protective stone at water lever.  On the bed of the Cooper River, the base of each island covers five acres.  The islands are made of Newfoundland limestone, with some of the individual stones weighing up to two tons.

Each of the stay cables is housed in a high-density polyethylene (HDPE) duct, comprised of many sections butt-welded together.  Each duct section is composed of two layers of co-extruded HDPE, so that there is an inner black layer and an outer white layer.  Along the entire length of the ducts are double helical ribs designed to shed water and increase aerodynamic stability.  At the roadway level anchorages, all of the stay cables are fitted with internal dampers, which are sealed to prevent water infiltration.  In addition to these internal dampers, the longest 16 cables in the main span are fitted with fixed external dampers.  Although the bridge does not currently have cross tie cables, the longest 24 cables in the main span are equipped with steel collars to allow the future addition of cross ties, if necessary.

Vertical Access was appointed by Freyssinet to document conditions on a representative sample of the bridge’s stay cables as the first phase of a warranty inspection schedule.  Each tower supports 64 cables and is equipped with two elevators, one on each side of the roadway.  Kent, Donn, Mike, and Keith were able to access the tops of the towers to begin the cable inspections using the construction elevators.  Their first day on site yielded slow progress and a lot of learning, which was to be expected given this was VA’s first exposure to a cable stay bridge.  The following days brought faster progress and a lot of jumaring.  Midweek thunderstorms forced the team to take a much-needed break, and allowed them to explore downtown Charlestown.   By the end of the week the Vertical Access team had jumared close to 2 vertical miles, eaten authentic southern grits, and was ready to head back to Ithaca for some office time.