The $540 Million Super-Strong, Robust Cable-Stayed Bridge In Charleston
Want to know more about the longest cable-stayed bridge in North America?
Located in historic Charleston, South Carolina, the $540 million Arthur Ravenel Jr. Bridge served as a landmark northern gateway when it was opened to the public mid-July 2005 after a week-long community celebration.
Replacement For Grace And Pearman Bridges
The bridge over the Cooper River was designed by Parsons Brinckerhoff in 2001 and built by Palmetto Bridge Constructors (PBC) to replace the two old, outdated and deteriorating cantilever truss-type bridges – the Grace and Pearman Bridges. The engineers tasked to improve vehicle and truck transportation in South Carolina as well as protect the multibillion-dollar container trade not only had to focus on the bridge design but had to deal with:
- a history of devastatingly-strong earthquakes that almost leveled Charleston
- mega hurricanes such as Hugo in 1989
- occasional out-of-control container ship
Robust And Strong Bridge
The engineers and workers onsite were to construct a robust bridge that is flexible and able to bend and move and remain standing. In the end, the bridge design made sure that it can withstand up to 300 mph (480 kph) wind gusts , a Category 5 hurricane which is a constant threat in the area, and up to a magnitude of 7.4 on the Richter scale. The engineers built 1-acre rock islands around the towers to ensure that ships would run aground before ramming and possibly seriously damaging the bridge.
The New Arthur Ravenel Jr Bridge aka New Cooper River Bridge
The 8-lane Arthur Ravenel Jr. Bridge, also called New Cooper River Bridge is the longest cable-stayed bridge in North America. The bridge serves a daily traffic volume of 80,000 vehicles on the heavily-traveled US Route 17. It runs from Charleston to Mount Pleasant in South Carolina with the longest span at 1,546 feet (471 meters) and the total length of 13,200 feet (4.0 km).
The New Cooper River Bridge uses cables that are anchored, bolted and fastened by 302 stainless steel special washers to the diamond towers to support a road deck and roadway. The diamond towers extend 575 feet above the road and the cables attached to the towers can hold more than 500 tons. The strongest of the 128 cables on the bridge are comprised of 90 separate 7-wire stands twisted and formed together. The cables are protected from the natural elements by a high-density polyethylene (HDPE) pipe, 12 to 20 inches in diameter, wrapped around the cable.
8 Lanes And A Pedestrian/Biker’s Path
The road is set at a height of 200 feet above the average high tide line, making adequate allowance for swells and abnormalities. With eight 12-foot lanes, four in each direction dedicated to vehicles, a 12-foot path or side lane for runners, walkers and bicyclists was added, running along the entire south edge of the bridge overlooking the Atlantic Ocean and Charleston Harbor. The path extends from Patriots Point Road on the Mount Pleasant side to East Bay Street on the Charleston side, at approximately 2 miles long. The path’s slope is between 1.8% and 5.6%.
Eye-appealing features were recommended by San Francisco-based MacDonald Architects which include:
- sloping light poles on the bridge’s approaches to match the sloping cable
- slanting piers to complement the diamond shape of the towers
The prominent feature of the bridge which was selected by public consensus is the diamond-shaped towers. Suspended between the legs of the tower, the roadway is at no point directly connected to the towers. The road deck is actually what the stay cables fully support.
The Need For A Wider And High-Clearance Bridge
Before construction of the Arthur Ravenel Jr Bridge, the first bridge over the Cooper River was a narrow 2-lane toll bridge (Grace Bridge) which opened in 1929. In 1966, a second span (Pearman Bridge) was built to support the increasing traffic. But by the 1980s, the two bridges were overwhelmed by the huge traffic buildup. To make matters worse, the older bridge showed signs of falling apart. When large container ships started to come in, the older bridges were deemed too low for the new Panamax boats, necessitating the construction of a new bridge with wider span and higher clearance to support the seaport activities of Charleston.
Dedicated To South Carolina State Senator
It was through the efforts of then South Carolina State Senator Arthur Ravenel Jr that the bridge got its funding. In April 2002, the first foundation work started. A drilled-shaft foundation is required by the design instead of pile driving to reduce the noise for nearby residents and less disturbances to existing bridges. The soft soil on site forced crews to drill 240 ft. to a deeper clay layer with 12-ft. diameter shafts. Steel girders sit atop a series of pier caps and columns, on the high level approaches while the interchanges used concrete girders.
Design-Build Construction Approach
The bridge’s general contractor, PBC self-performed 80% of the work. Around 600 PBC employees and 200 subcontractors worked on site at the peak of construction. Constructing under a design-build method allowed them to split the project into five jobs-each interchange, each high-level approach and the main span. With very little overlap, the project stayed ahead of its fast-paced construction schedule.
A self-climbing form system to build the towers was used wherein the formwork provided a solution to meet the tight construction tolerances and give the laborers working hundreds of feet in the air safe access. The system did not require the cranes to spend time raising the forms after concrete hardening on each segment but were instead used to haul material from the barges.
By 2004, the first stay cables were hung from the towers and sections of the road deck were built outward as more cables were hung. Simultaneously, the decks of the approaches were also taking shape. Part of the roadway was constructed over the top of the old cantilever bridges which remained open to traffic while construction of the new bridge was ongoing.
July 2005 Opening
A week-long celebration which included concerts, dinners, public bridge walk, and fireworks culminated in the dedication and opening of the new bridge on July 16, 2005. The project was completed one year ahead of schedule and saving the taxpayers $150 million.
Have you seen this great bridge?