A construction error six decades ago might be the cause of a steel beam fracture discovered Friday on the Delaware River Bridge, reports The Philadelphia Inquirer.
The crack, which cleanly separated a 14-inch truss below the westbound lanes, was discovered by New Jersey Turnpike Authority workers Friday, causing authorities to shut down indefinitely the span that connects the Pennsylvania and New Jersey turnpikes. It is unknown when the fracture occurred.
Engineers estimate they will need at least two weeks to determine the repairs required to fix the heavily traveled bridge between Pennsylvania and New Jersey.
The cause of the crack, considered highly unusual, have some experts suspecting a flawed, 60-year-old weld.
Karl Frank, professor emeritus of engineering at the University of Texas at Austin, said Monday he suspects holes were mistakenly drilled into the truss during construction and were filled with plug welds that were defective and eventually gave way.
“It’s incredibly unusual for steel to break like that,” said Joe Martin, an engineering professor at Drexel University in Philadelphia. “Pieces don’t break. They stretch, they twist, they give you some warning to get out of there. Fractures are the bridge engineer’s nightmare.”
Martin agreed with Frank’s assessment, adding: “We would never allow that today.”
The 61-year old, 1.2 mile long bridge carries more than 42,000 vehicles per day on Interstate 276 over the Delaware River and is jointly owned by the Pennsylvania and New Jersey turnpikes.
Crews are working to stabilize the bridge and have installed steel plates to brace the fractured truss. The bridge sank a bit, so crews will be jacking the bridge back to its original position. The bridge will be supported by eight temporary towers until a permanent fix is made.