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Wando Bridge designer: 1 broken cable would not make bridge unsafe for driving

Snapped cable discovered in James B. Edwards Bridge over Wando River. (SCDOT)

The engineering firm that designed the James B. Edwards Bridge over the Wando River on I-526 says only one of the bridge's support cables breaking wouldn't make the bridge unsafe to drive on.

The westbound portion of the bridge remains closed Wednesday as the S.C. Dept. of Transportation assesses the extent of damage and repair plans after one of the support cables in the bridge structure was found to be broken.

DOT Director Christy Hall said Wednesday cable repair and replacement materials were en route to Mount Pleasant. However, Hall and Gov. Henry McMaster said the bridge closure and repair process "won't be over in a matter of a couple days."

Representatives for FIGG Bridge Engineers, which South Carolina contracted to design the Wando bridge in the late 1980s, say there are numerous such cables within the bridge's underlying support structure.

Cheryl Stopnick, a spokesperson for FIGG, said Wednesday that the cables within the bridge structure, known as pre-stressing tendons, provide tension to support to the bridge deck in order to withstand the load of traffic.

Only one of those tendons rupturing "would not compromise safety," but authorities closing the bridge to investigate issues is common, Stopnick said.

Additionally, Stopnick says, the two east and westbound sections of the James B. Edwards Bridge are designed to carry much heavier loads than they do.

"It was designed to carry three lanes of traffic, but it only carries two," Stopnick said.

FIGG designed the bridge according to DOT specifications, Stopnick says, but didn't actually construct the bridge. The James B. Edwards Bridge was constructed by Louisiana-based contractors T L James and Associates.

According to Stopnick, the Wando Bridge is constructed of pre-stressed concrete, as are the majority of bridges in the firm's portfolio. Stopnick says federal highway authorities have deemed pre-stressed concrete bridges the "most durable structure type for bridges." They're also the most common.

It's unclear at this point if it's only one cable that requires repair on the bridge. According to DOT, there are 92 support cables within the bridge, encased in segmented concrete blocks that make up the base of the bridge deck.

DOT said it discovered water intrusion and deterioration of "cables" within the bridge structure during its inspection Monday, but engineers don't know what caused the rupture of the one cable.

"There have been instances of pre-stressing tendons that have experienced corrosion due to improper construction and/or maintenance that over time led to water penetrating the protective layers and corroding the steel," Stopnick said.

The Dept. of Transportation said Monday it has been doing weekly site assessments of both the west and eastbound portions of the Wando bridge since 2016, when a damaged cable was first discovered. That cable was repaired.

The ruptured cable discovered Monday was not the same one previously repaired, according to DOT spokesman Pete Poore.

FIGG says replacing tendons for long-term damage is an infrequent occurrence relative to the number of tendons installed in bridges throughout the U.S. and the world.

Detours have been set up along U.S. Highway 17 in Mount Pleasant for traffic impacted by the bridge closure.

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