The weekly inspection that found a cracked support cable under the Wando River bridge is a sign of serious trouble for the critical 1½-mile span.

Federal regulations require a general inspection of highway bridges every two years. That schedule gets bumped up if the bridge is discovered to be deficient or weight limits have been required, according to the Federal Highway Administration.

But if a bridge is inspected every six months, that means the span has something chronically wrong, said a veteran concrete bridge engineer who asked not to have his name used because he consults with state transportation departments.

Another expert, Richard Rice, a director of the National Academy of Forensic Engineers, formerly worked on the Don H. Holt Bridge stretch of I-526. He agreed the weekly inspections are an ominous sign, calling it remarkable the span is examined so often given the cost in money and manpower to do it.

The westbound lanes of the James B. Edwards Bridge over the river on Interstate 526 were closed Monday after a weekly "review" inspection discovered a crack in one of eight main cables that support it. The reviews have been made since 2016, when one of the cables broke near where the damage was discovered Monday.

S.C. Department of Transportation officials said Wednesday that a team of experts is feverishly working to pinpoint the cause of the rupture. Replacement cable for temporary repairs arrived at the bridge on Wednesday, but the span will likely be out of commission until at least June 11, shutting down a mainstay for S.C. Ports shipping and an essential commuter artery connecting Mount Pleasant to Daniel Island and North Charleston. 

Rice, however, wonders if the long-term prognosis will be even worse because the two compromised cables were found so close together. A permanent shut-down could loom if the integrity of the bridge is found to be at risk, he said.

"Nothing is out of the ballpark," he said. "The bottom line is, there are just so many things to look at."

State Rep. Nancy Mace, R-Daniel Island, wrote state Secretary of Transportation Christy Hall seeking answers to a host of questions, including how many of the 92 cables supporting the bridge are being monitored and for how long. 

Corrosion issues

The $32.1 million Edwards bridge is a box-girder concrete construction that uses cable "tendons" to support the weight of the concrete itself. The design began to see widespread use in Europe to replace bridges destroyed during World War II. It became popular in the United States in the 1960s as a more affordable and efficient type of construction.

Corrosion of the box girder cables quickly became a problem and a variety of methods are used to control it. Poor grouting is the usual culprit, and grouting problems have been identified on the Edwards bridge. Grouting is filling gaps in the concrete to keep water off the cables.

Problems with the Edwards Bridge have been long known. Issues with the bridge's joints were found four years after it opened, and cable corrosion issues were cited in a 2011 Clemson University graduate engineering thesis. 

Corrosion from water seepage was found near where the crack occurred, transportation officials said. They confirmed Wednesday they have been seeking equipment to monitor the cables for breakage since 2002.

The cables on the Edwards Bridge are set in the housing underneath the bridge itself. They apparently were made of steel more susceptible to corrosion than other types, said Martin Gordon, an engineering technology professor at Rochester Institute of Technology, after looking over a photograph of the cables.

Gordon, president of the National Academy of Forensic Engineers, is an expert in the field that examines engineering failures to determine what happened and prevent future failures.

“Why would you put cables underneath the surface of a bridge you know is going to get water intrusion in a corrosive (saltwater) environment?” Gordon asked. “It doesn’t seem like a great idea to me.”

Explosive population growth in the region also could have generated more vehicle traffic than engineers planned for in the designs. More vehicles means more fatigue on the structure and a greater chance for failures, Gordon said.

A salty environment in combination with fatigue "can cause material failure," Gordon said. "Until you actually build it, there’s no way to tell if it will truly be a safe, reliable, robust design."

Severely corroded cables led to the 2009 closing of Cline Avenue Bridge over a shipping canal in East Chicago, Ind. The closing, and eventual demolition, came after the bridge operated for 26 years.

The problems first were noticed on the box-girder bridge 10 years earlier. An Indiana Department of Transportation report called it a structural deficiency.

Design defense

The Edwards Bridge was designed by Tallahassee-based FIGG Bridge Engineers, a renowned firm that has designed a host of iconic spans, including the Sunshine Skyway in Florida.

FIGG is known for its innovative designs, but when engineers design megastructures like new bridge styles, they cannot build full-scale models for testing.

Cheryl Stopnick, a spokeswoman for FIGG, said the company has heard nothing from South Carolina transportation officials regarding the closure of the Wando River bridge. She said the bridge was designed in a manner that has produced some of the most common and durable spans in the nation.

These bridges, made of reinforced concrete, are designed to handle far larger loads than they normally experience, Stopnick said. For example, the Wando River bridge was designed to handle the load of three lanes of traffic in each direction, even though the span is limited to two, she said.

The bridge was also designed to meet national standards that anticipate heavy truck traffic, Stopnick said.

“The volume of truck traffic would not decrease the life of the structure as long as the bridge continues to be properly maintained by the owner,” she said, noting that South Carolina's Department of Transportation has "has well-established capabilities in bridge management."

After the bridge opened to traffic in 1991 — two years behind schedule — the transportation department and its contractor, T.L. James Associates of Louisiana, sued each other. The DOT faulted the contractor for delays while T.L. James said the project lag was due to the design for the bridge being incomplete and defective. The department eventually shelled out $4.9 million to settle the lawsuit.

T.L. James Associates got out of the construction business in 1998, and everyone associated with the bridge project "are long gone now," according to a woman who answered the phone at the company's headquarters Wednesday.

Figg and Muller, a company related to today’s Figg Bridge Engineers, were among the engineers who worked on the construction of the Cline Avenue bridge Indiana. The company blamed the contractor for the corrosion. Figg was hired to design the replacement bridge under construction today.

Glenn Smith contributed to this story.

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Science and environment reporter. Author of Washing Our Hands in the Clouds.