Work crews were called off the Murray Morgan Bridge rehabilitation project Wednesday after two 240-pound pieces of steel fell off the bridge and into the Thea Foss Waterway.
No one was hurt in the incident, which took place about 1:30 a.m.
City engineers say work on the bridge will be delayed for at least a week and a half for inspections and repairs.
The inch-thick steel plates, each measuring about 2 by 3 feet, were part of a temporary structure built to hold the moveable span of the drawbridge in the open position, said Tom Rutherford, the city engineer in charge of the project.
The temporary structure was built to relieve tension on the counterbalance mechanism so the 9-foot-in-diameter pulleys, or “sheaves,” at the top of the bridge could be replaced.
“We don’t know whether it was because of wind or temperature change or what, but the lift span moved a little bit,” Rutherford said Wednesday. “Some people said they heard a bang and a splash. We’ve been out there ever since, making sure nothing else is moving or loose.”
The steel plates had been wedged between the bottom of the lift span and force-measuring devices called “load cells,” Rutherford said.
When the moveable span tilted, it also bent some of the construction scaffolding, which will need repair and perhaps a redesign before work continues, Rutherford said.
The bridge contractor, PCL Construction, had planned to begin removing and replacing the first of the four sheaves today. Now, Rutherford said, that work is not likely to start for at least another week and a half, depending on what repairs and design modifications are necessary.
The Murray Morgan Bridge, also known as the 11th Street Bridge, opened to traffic in 1913 and is on the National Register of Historic Places. The $57.4 million rehabilitation project began in 2010 and is scheduled to be completed in April.