The sudden closure of the Ben Sawyer Bridge on Monday — caused by "extreme heat" that expanded its steel structure to where it became stuck partially open — is a relatively rare occurrence and not a sign of a problem with its structural integrity, state transportation officials said.
Coastal South Carolina has experienced record-setting high temperatures in recent days. The Charleston area on Monday experienced a high of 100 degrees, with an even higher heat index — hot enough to warp the steel bridge.
Though other bridges in the state have experienced similar temperatures, Memorial Day marked the first time the Ben Sawyer Bridge was forced to shut down due to the heat, according to the S.C. Department of Transportation.
“This can impact the opening/closing of the bridge,” DOT said in a tweet.
The bridge remained shut down to vehicle traffic for four hours during the evening, much to Memorial Day beach-goers’ dismay. It eventually reopened to traffic around 9 p.m., but it remained closed to maritime traffic Tuesday.
"It isn't common, but it's not unheard of," Kevin Turner, a DOT construction engineer, said of the bridge’s thermal expansion.
The bridge is expected to be reopened to all traffic by 5 a.m. Wednesday, Turner said. He said the bridge opens for boats about 200 times a month, about seven times a day.
Turner estimated the state has seen three similar bridge problems caused by excessive heat during the last 10 to 15 years, including the Lady's Island Bridge in Beaufort.
The last non-routine maintenance done on the Ben Sawyer Bridge was in October when a limit switch needed repair, Turner said. That switch is a light sensor that calculates the alignment of the bridge when it opens and closes.
With the bridge stuck partially open Monday, motorists trying to get off Sullivan’s Island were re-routed a few miles away to the Isle of Palms connector, the only other vehicular route off the islands. Officials used a fire hose to cool the steel.
After the metal had cooled enough, engineers removed a small portion of a swollen plate by taking a torch to the surface and essentially melting it away so that the bridge could again open and close, according to DOT.
John Ryan, an assistant professor of civil engineering at The Citadel and who also runs Ryan Structural Engineers, was in contact with Sullivan’s Island officials Tuesday to learn more about what happened.
“They torched away about a quarter of an inch … across one plate,” Ryan said. "My understanding is, from a structural standpoint, it was almost cosmetic … it doesn’t impact the function of the bridge whatsoever as far as I can tell.”
Sullivan’s Island Town Administrator Andy Benke said the bulk of involvement by local officials consisted of traffic control, with help from Isle of Palms and Mount Pleasant police.
Ryan did not fault DOT or local officials’ for their response to the issue.
“I’m not sure that there is a fundamental action to be taken,” he said. “It seems DOT … was able to respond to it in a relatively quick fashion.”
The current steel truss Ben Sawyer Bridge was put in place in January 2010 — it was built at the former Charleston Naval Base and hauled to the site by barge. Its installation required closing both the waterway and the roadway at different times over 10 days.
The 2010 replacement came after years of structural issues with the previous swing span bridge.
In 2009, the 124-foot bridge was closed for 72 hours so rusty steel beams supporting its 5-ton bridge-tender’s house could be replaced.
In 2004, transportation engineers reduced the gross weight of vehicles allowed to cross the bridge to 20 tons from 30 tons after an inspection found “fairly significant deterioration” of floor beams and stringers.
The old bridge also was pummeled by Hurricane Hugo in 1989, and its tilting, cockeyed swing span became one of the most iconic photos of the damage caused by that storm.