Main Street Bridge project completed

By James Grob, jgrob@charlescitypress.com

It had been almost 25 years since the Main Street Bridge in Charles City had any major work done to it, and Charles City City Engineer John Fallis hopes the historic bridge will last for at least 25 more.

“I don’t see why we couldn’t get another 20-25 years out of it,” Fallis said. “I expect the bridge could last until the middle of the 21st century before building a new bridge will be a requirement.”

The bridge repair project, which was just completed, primarily focused on correcting the undulations of the roadway surface caused by settlement and displacement of the earthen fill within the arches. The depressions in the street surface prevented storm water from flowing to intakes and allowed water to leach into the earthen fill. This has appeared to exacerbate the settlement issues.

Polyurethane material was injected under the street and sidewalk pavements and first placed within the bridge’s arches to solidify the existing fill material. Additional polyurethane material was then placed to lift the pavement and sidewalks into place to re-establish roadway drainage to the intakes.

Fallis said it was 1997 when the bridge last received that much work. The 1997 project was performed to repair existing concrete surfaces, removal and replacement of sidewalks, and removal and replacement of storm sewer intakes and outlet pipes.

He said the bridge was originally constructed in 1910 as a concrete spandrel, commonly referred to as an “earth filled arch bridge,” The bridge has been recognized as a historical and iconic bridge for Charles City, and is listed on the National Register of Historic Places.

“We made sure that wouldn’t be an issue with this project,” Fallis said.

Fallis said the U.S. Corps of Engineers reviewed the scope of the 2020 project and provided a “No Adverse Effect” finding to the State Historic Preservation Office, meaning the repairs do not impact the historic preservation of the structure.

According to the Iowa DOT, the bridge carries approximately 6,000 vehicles per day. Fallis said that even at the bridge’s age of 110 years, it does not suffer from structural deficiency.

“It’s in good condition, to the point where it works against us sometimes,” Fallis said. A lot of your bridge replacement funding is really set up for structurally deficient in obsolete bridges. When you have a relatively good bridge it’s hard to find the funding because you can’t find funds out there.”

The repair project was completed at a cost of $327,059.80. It was funded by city dollars — a local option sales tax, road use tax money and general funds. Fallis said the local option sales tax is an “extremely vital source of funding for our roads.” Jasper Construction out of Newton was the general contractor.

Fallis said that the bridge is located immediately downstream from the Main Street dam, which creates turbulent flow through the bridge opening and agitates the stream bed material on a consistent basis. As part of the preliminary design for the bridge repair project, an underwater investigation was completed to determine the extent of streambed scour at the bridge’s piers and abutments.

The findings were compared to an underwater inspection completed in 2005. Overall scour is not an issue since the stream bed is primarily on bedrock, Fallis said. There were areas of localized scour, and those areas have been protected by placement of revetment stone as part of the bridge repair project.

The project also included the repair of spalled and cracked concrete on the wing wall at the northwest corner of the bridge.  At the time of construction, it was determined the condition of the wing wall required the placement of a structural wall “jacket” to reinforce and protect the existing wall.

Fallis said that painting the bridge was also discussed, and the city received estimates that were all in excess of $100,000. The city determined that a paint job was not cost efficient at this time

“We wanted to protect the structure and extend the life of the bridge,” Fallis said. “That’s what this project was really about, it really wasn’t about the aesthetics of the bridge.”