CHICAGO (CBS) — City officials have reopened the northbound lanes of the Lake Shore Drive bridge over the Chicago River, a day after the span was closed due to cracked steel support beams.

Crews spent hours installing shoring towers under the northbound lanes of the bridge to support the bridge until permanent repairs can be made to the damaged beams. The towers raised a dip in the road by six inches.

The northbound side of the bridge reopened to traffic shortly after 1 p.m., hours ahead of the Tuesday evening rush.

Chicago Department of Transportation Commisioner Rebekah Scheinfeld said it took a “Herculean effort” by city crews working around the clock to install shoring towers to reinforce the bridge.

Officials also conducted a full inspection of the bridge after installing the shoring towers before reopening the area to traffic. Scheinfeld said she is confident the bridge is safe for vehicles.

“We would not be reopening this roadway unless we felt fully confident it was safe.” she said.

The northbound lanes of the Lake Shore Drive bridge over the Chicago River were closed on Feb. 11, 2019, after crews found cracked steel beams. (Credit: CBS)

Permanent repairs are expected to take several weeks, according to Scheinfeld.

A city worker repairing traffic lights nearby spotted large cracks in steel beams under the bridge late Monday morning, prompting the city to close the northbound side of the bridge.

Scheinfeld said officials believe the crack was caused by corrosion, which was exacerbated by the recent extreme weather, which saw temperatures fall under 20 below zero for two days in a row at the end of January, and then rise to the 50s just days later.

Long-term repairs likely will include attaching new steel plates to reinforce the existing girders. Scheinfeld said officials are still researching how repairs will be made without entirely shutting down the bridge again.

Dr. Gongkang Fu, department chair of civil engineering at the Illinois Institute of Technology, said such large cracks in bridges are very dangerous.

“This issue may exist in other spaces, in other beams as well,” he said.

One in five of Illinois bridges are deemed structurally deficient.

“Illinois’ situation is, I believe, below average,” Fu said.

And while this bridge passed its latest inspection in 2017, a state document shows problems including cracks and minor deterioration were reported even then. That damage is almost two years old now. And the recent extreme cold wasn’t doing it any favors.

“A small crack can be so small our eyes won’t even be able to tell,” Fu said.

He said it only takes a few days “for it to fracture to this big.”

Ed Maher, the communications director for the International Union of Operating Engineers says the close call should serve as notice to all lawmakers that infrastructure problems must be addressed.

“This is a warning sign and I would say that we got off lucky,” Maher said. “Think of how much worse this could have been.”

Maher said it was fortunate that no one was seriously injured or killed. He said injuries could have happened if the break had happened in the middle of Lake Shore Drive instead of to the side.