How It's Built: The Arthur Ravenel Jr. Bridge
If you're into construction and engineering, you probably already know that bridges are fascinating structures. And when a bridge stands 2.5 miles across a large river? That's an amazing engineering and design accomplishment. That's why the Arthur Ravenel Jr. Bridge, also known as the New Cooper River Bridge, is one of the most famed bridges in North America.
About the Arthur Ravenel Jr. Bridge
Located in Charleston, South Carolina, the Arthur Ravenel Jr. Bridge was built to cross the Cooper River and connect Downtown Charleston to the east side of the river. While this bridge was finished in 2005, there were two bridges that existed before the New Cooper Bridge was constructed: the John P. Grace Memorial Bridge and the Silas N. Pearman Bridge.
Completed in 1929, the John P. Grace Memorial Bridge was the first bridge to cross the Cooper River. The bridge was named after the city's then-serving mayor, John P. Grace, who was campaigning diligently for it to be constructed. Once finished, it was about 2.7 miles, or 4.3 kilometers long, and was the fifth-longest cantilever truss bridge in the world. It took 17 months to finish construction and cost about $6 million. However, while this bridge was a great engineering feat for the time, it had steep roads with grades of about 6 percent, narrow lanes, and tight corners that were not sustainable for long-term safety and traffic requirements.
By the 1960s, the Grace Memorial Bridge needed to be modified. Changes and upgrades were made to make the original build more accessible, but it ended up making lanes even more narrow. What had originally been designed for classic cars like the Ford Model A was becoming obsolete, however, the bridge continued to stay open. Meanwhile, a new bridge was to be built parallel to the Grace Memorial Bridge to support increasing traffic. They named this new structure the Silas N. Pearman Bridge.
Constructed in 1966 for about $15 million, the new bridge was named after the serving South Carolina Highway Commissioner of the time. It was three lanes wide, so it provided more access to people commuting and was designed specifically for drivers who were going northbound, while the Grace Memorial Bridge became designated for people heading southbound.
By 1995, there had already been much conversation about needing a new bridge to cross the Cooper River as engineers had argued that the John P. Grace Memorial Bridge had been rendered obsolete due to a lack of upkeep. However, many local politicians needed specific justification in order to invest more government money into a new bridge. Once officials released proof that the Grace Memorial bridge scored a safety score of only 4 out of 100, the stamp of approval was given to start campaigning for a new bridge.
Retired Congressman Arthur Ravenel Jr., for who the bridge was later named, ran for the South Carolina Senate with the core focus of fundraising and campaigning for the new bridge. He worked with local, state, and federal officials as well as the South Carolina Infrastructure Bank to fundraise for the project and create partnerships and agreements for final approvals.
The new bridge was to be designed to carry upwards of 100,000 vehicles a day and be eight lanes wide. It was also important that it would be pedestrian-friendly for those who wanted to bike or run across the bridge. In fact, the bridge hosts an annual USA Track & Field 10,000 meters competition, the Cooper River Bridge Run, on the first weekend of every April. When the New Cooper Bridge opened on July 16, 2005, it was the then-longest cable-stayed bridge in North America.
The Difference Between Suspension Bridges and Cable-Stayed Bridges
We've written about how a few suspension bridges like the Royal Gorge Suspension Bridge and the Golden Gate Bridge were built, but before we go further about the Arthur Ravenel Jr. Bridge, we wanted to discuss the main engineering differences between suspension bridges and cable-stayed bridges.
Although both cable-stayed bridges and suspension bridges might look similar to the casual viewer, the way they differ is in how the cables are connected to the tower. In suspension bridges, the cables extend across the entire length of the bridge, helping to transmit the load to both ends of the bridge where the load is being carried. In cable-stayed bridges, the cables are directly connected to the towers, which have a strong foundation and carry the load themselves.
Essentially, the ways in which the two types of bridges hold and distribute weight are different. However, cable-stayed bridges are typically less costly due to the fact that they require much less steel cable, and they can be built much more quickly.
How the Arthur Ravenel Jr. Bridge Was Built
In order to simplify the construction process, the bridge was built using the design-build method. While this meant that the construction would begin before the design of the bridge was finished, it was the best bet for getting the project done within the desired five-year timeframe. It also meant that both the design and construction of the project fell under one company, which typically increases communication and efficiency on the job site. The company that built the bridge was a joint venture project between two large construction companies that used the name Palmetto Bridge Constructors.
The project broke ground in 2001, about six years after all the stakeholders had confirmed that a new bridge was needed to span the Cooper River to support increased transit demand. The State Infrastructure Bank (SIB) estimated that it would cost about $325 million to make, with $96.6 million coming from the Federal Highway Administration and a $215 million dollar loan coming from the SIB.
In order to make things move more effectively, Palmetto Bridge Constructors decided to split the project into a five mini-project approach. The goal would be to have different groups of laborers build the two highway interchanges at either end of the bridge, the two approach spans, and the cable-stayed span, all at the same time.
By the summer of 2002, the foundations for the towers over the cable-stayed span were mostly in place, as were the rock islands around them. Soon after, the construction of the steel and concrete towers took place. Due to the desire to have the project done within that five-year timeline, contractors used a self-climbing technique to build the towers. This not only made the work safer for the construction workers, but it also meant that the cranes could work more efficiently to move material from barge ships below.
In 2004, in order to save time, the first cables were hung despite the towers not being fully done. As more cables were hung, more of the deck was built out from each of the towers. By March of 2005, the last piece of the deck was built and a ceremony was held. However, paving, installation of lights, signage, and cleanup still needed to be done so the bridge did not open officially until July of 2005.
As mentioned above, each of the towers has a rock island around them. This may seem odd at first, but their purpose is very intentional. As the Cooper River is a common ship port for both commercial and entertainment use, many ships are passing under the bridge at any given time. The rock islands exist in order to prevent the bridge from any potential accidents that may happen in the waters underneath. If any ship were to crash into the towers, massive structural damage could happen and lives could be at stake. In order to protect the bridge, the rock islands exist as a barrier for any ships passing through.
Lastly, because South Carolina may experience extreme weather like hurricanes and other natural disasters, the bridge had to be engineered to withstand heavy winds. As such, the bridge is designed to withstand winds over 300 mph which would be much more powerful than any storm the area has ever faced, proving the designers and engineers were extremely cautious with their estimates.
When all was said and done, the Arthur Ravenel Jr. Bridge stood 573 feet tall from the top of the tower to the waters below with the deck being 186 feet above the river. The bridge is eight lanes wide with four going in each direction. The total length of the bridge is 13,200 feet, right around four kilometers, with the distance between both towers at 1,546 feet. The bridge opened to traffic on July 16 of 2005, one year ahead of schedule. The bridge is an amazing accomplishment and a significant piece of the Charleston skyline.
