A permanent splice on the fractured Delaware River Bridge was completed about a month ahead of the estimated schedule. The 1.25-mile-long bridge connecting the Pennsylvania and New Jersey turnpikes on Interstate 276 opened to traffic on March 9 for the first time since it was closed on Jan. 20 after a complete fracture was discovered in the superstructure beneath the westbound lanes on the Pennsylvania side of the bridge.
The 61-year-old symmetrical truss bridge—which carries about 42,000 vehicles per day—is jointly owned by the Pennsylvania Turnpike Commission and New Jersey Turnpike Authority. Aside from PTC and NJTA employees, the joint repair team included at least two dozen contractors, consultants and other entities.
“Thanks to a round-the-clock effort involving dozens of engineers, contractors, scientists, and other workers, we are able to get that done much sooner than we expected with every confidence that it will be safe for the motorists who depend on it,” New Jersey Transportation Commissioner Richard T. Hammer, who serves as chairman of the New Jersey Turnpike Authority board, said in a statement.
New Jersey Turnpike Authority Executive Director Joseph W. Mrozek said, “We were able to bring in some of the very best minds in the field to work with the staffs of our agencies to evaluate the fracture and then design and execute the repair. Because of hard work by a lot of talented people, we’ll be reopening the bridge weeks ahead of the date we projected when it was first shut down.”
A series of load tests to study permanent splice was successful shortly before the bridge reopened to live traffic. The test involved monitoring sensors on the truss and splice while eight, tri-axle dump trucks carrying 40 tons of aggregate drove across the bridge.
“We will continue to monitor loads and stresses on the bridge,” NJTA Chief Engineer Robert Fischer said in a statement. “The temporary sensors will remain for now. In the coming months, we expect to install a system for monitoring the health of the bridge over the long term.”
PA Turnpike Chief Engineer Brad Heigel said in a statement, “Given the number of experts who have inspected, tested and studied it over the last 49 days, it’s safe to say this bridge is perhaps the most scrutinized structure in the nation and maybe the world.”
He went on to say, “We have a high level of confidence on both shores of the river regarding the reliability of our repair and the safety of the bridge for travelers and for nearby residents.”
The bridge was first opened in 1956. Heigel said the primary factors contributing to the fracture was age and plug welds that were commonly used in the 1950s to fill mistakenly drilled holes. While two mis-drilled holes approximately one inch in diameter were filled with weld material, the team didn’t find any other plug welds on the bridge after weeks of hands-on inspections, ultrasonic testing and metallurgical analysis from three different, independent laboratories.
“We continue to look at other factors such as air temperature and loads like heavy trucks or high winds that may have had an impact when the fracture occurred,” Heigel said. “But getting a definitive answer as to why it happened is akin to solving a 60-year-old mystery perpetuated by unseen offenders. We may never know for sure what all the factors were that caused the fracture.”
Two days after the closure, an operation to install eight temporary steel plates to stabilize the fracture was completed. The fracture caused a section of the bridge between the two supporting piers to drop by about two inches and the load carried by the cracked member was transferred to adjoining structural components that aren’t designed to carry heavier loads.
The team constructed eight, 80-ft-tall towers for hydraulic jacks capable of lifting 600 tons each to realign the truss before a post-tensioning technique was used to bring the damaged truss back into alignment and to reintroduce loads into the fractured truss member. Finally, the team built a permanent splice to rejoin and repair the fractured truss member.
“The repaired truss member is now much sturdier than the original because of the splice,” Heigel said.