A temporary, reusable, steel bridge that can span a washed out creek bank was installed in mid-November in South Carolina. The crossing carries approximately 2,100 vehicles daily to a local high school and a nuclear power station, so bringing a replacement crossing online quickly was important to the South Carolina Department of Transportation. SCDOT
A temporary, reusable bridge opened in South Carolina this month, providing a crossing for a high-volume route after flooding destroyed the existing bridge.
November 26, 2013—South Carolina experienced record-breaking rainfall amounts this summer: an average of 26 in. per month in June, July, and August. The storm water washed out 91 roads and damaged 15 bridges and 52 pipes, according to the South Carolina Department of Transportation. Among this damage was a precast concrete bridge in Pickens County located along Jones Mill Road, a high-volume route that carries vehicles to and from a local high school and a nearby nuclear power station, the Oconee Nuclear Station. To bring the Six Mile Creek crossing back online as quickly as possible, the South Carolina Department of Transportation borrowed an idea more often seen used by the military: they turned to a reusable, galvanized steel crossing that could be erected quickly and then moved to another area of need once the school year ended and a permanent crossing had been built.
Following a significant deluge on August 6, the normally 18 to 24 in. deep creek began running at almost 14 ft, according to Richard “Lee” Floyd, P.E., the state bridge maintenance engineer for the South Carolina Department of Transportation (SCDOT), who wrote the special provisions for the reusable bridge that replaced the damaged existing structure. “We had a lot of debris loading [and] the existing bridge went into pressure flow. It damaged the substructure, and the bridge settled and was severely damaged,” Floyd says. The piles for the bridge were ripped up by the flow and a 10 to 15 ft section of one of the approach slopes was completely washed away.
On August 9 South Carolina Governor Nikki Haley signed an emergency declaration that enabled the SCDOT to request emergency relief funds from the Federal Highway Administration (FHWA), according to material provided by the SCDOT. The FHWA approved the request and approved the use of a temporary bridge by the end of the month.
Maintaining community connectivity was particularly important in this location, Floyd says, because of the high volume of traffic that needed to cross the bridge daily to reach the high school. Without the bridge, a 4.6 mi detour was the only option, which created a significant burden on students, their parents, and employees at the nuclear station. “[It] was very important that we get some connectivity reestablished,” Floyd says.
An unusually wet summer led to the partial collapse of the original
bridge. The normally 18 to 24 in. deep Six Mile Creek began
flowing almost 14 ft deep during an early August storm. The storm
water also washed away a 10 to 15 ft section of the creek bank.
The 150 ft long, 30 ft wide galvanized, high-strength steel bridge is similar in design to a parallel chord truss system, Floyd notes. Anchor bolts attach both sides of the bridge to concrete strip footings, and while one side of the bridge is fixed, a sliding expansion bearing on the other side allows for thermal expansion and shrinking. To protect the footings from any settlement that could potentially twist or damage the steel bridge, Floyd had steel piles added to reinforce the corners of the foundations. The piles extend to the bedrock 12 ft below the surface, he notes.
Because of the loss of slope on one side of the creek, the reusable bridge is 30 ft longer than the previous bridge at that location. “I just elected to buy a longer temporary bridge, and then when we get the permanent bridge, they can come in and regrade the slopes and we can do it right,” Floyd notes.
The bridge meets the American Association of State Highway and Transportation Officials (AASHTO) deflection and HS-20 live loading criteria and has been treated with an antiskid coating that enables the deck to perform in a comparable manner to asphalt. The reusable bridge was also designed to accommodate 1 1/2 to 2 in. of asphalt on the deck, should the antiskid coating not perform as expected, according to Floyd.
The temporary installation included reworking approximately 50-75 ft of the approach roadways on either side so that the bridge could be tied into the road, Floyd says.
The bridge “is like a big erector set,” Floyd notes. “You’re essentially building panels, and then hooking the panels together.” These temporary bridges can either be built entirely in a staging area and then pulled into position along rollers, he says, or built panel by panel and pulled out over the roadway as the new sections are added. “It just depends on how much room you’ve got and how comfortable you feel doing it,” he says.
But like an erector set, keeping track of all the components of your kit is the tricky part. Anyone attempting to use such a system must “make sure before you ship the bridge to the site [that] you inventory every part, every component, bolt, pin—everything,” He says. “When you get it to the site, you inventory it again. And when you take it apart, you inventory it again and inspect for damage.”
Also important, Floyd notes, is security. Because of the remote location, the possibility exists that people will walk off with steel components and try to sell them for scrap metal. At Six Mile Creek security measures and patrols used to protect the more easily accessible elements of the bridge from scavengers.
Charlotte, North Carolina-based Crowder Construction installed the bridge. The project represents the third time that the SCDOT has installed a temporary bridge to ensure community connectivity while a more permanent solution was designed and built.