Moser Tower in Naperville looks just fine to the untrained eye.
The tower is the 160-foot-tall structure that houses the chiming bells of the Millennium Carillon along the downtown Riverwalk, and it's been standing at the base of Rotary Hill since it was built in 2000 and completed in 2007.
But to the expert eye of engineers -- some of whom rappelled down the structure to get a closer look -- the tower has some issues.
Cracks and deterioration of its concrete walls could cause pieces to fall "without notice," and corrosion of structural steel connections could decrease the building's stability, a consultant found in a two-year, $50,000 study of the tower's condition.
"When we went out there, we found some of the deterioration was going quicker than you thought it would," said Bill Novack, the city's director of transportation, engineering and development.
The assessment determined a combination of maintenance, repairs and replacement of some parts will be needed to keep the $7.1 million Moser Tower in sound structural order.
Options include fixing the structure and maintaining it as-is, fixing it and improving the base to help prevent future corrosion, or maintaining it for a while and then tearing it down.
So the city is starting talks about how to approach the work, when to begin and how to pay for it.
"This is a beginning of the process," Riverwalk Administrator Jan Erickson said Thursday.
Consultant Engineering Resource Associates, Inc., of Warrenville, identified five options for work to shore up the tower, which range "from making it pristine all the way down to decommissioning it," Novack said.
Work could cost between $1.6 million and $3.7 million.
The most expensive options would involve upgrading the bottom of the tower to match original designs by Charles Vincent George Architects, which called for the lower 72 feet and 9 inches to be enclosed in glass and temperature-controlled, Novack said.
Enclosure plans were scrapped when the Millennium Carillon Foundation, which conducted the first phase of work in 1999 to 2001, ran of out of money.
When the city took over and completed construction in 2007, its main concern was to address issues with falling concrete that occurred in the early 2000s. The lower levels were left open to the elements, allowing moisture to seep in.
"Weather intrusion has caused premature corrosion and deterioration of the structure," the assessment reads.
Still, the tower is not a hazard for those listening to carillon concerts or walking along the Riverwalk, said Goeff Roehll, chairman of the city's Riverwalk Commission.
"We know, right now, it's safe," Roehll said.
But the assessment proves action should be taken within the next few years, Novack said.
The city council could decide to spend $3.7 million in a multiphase project or $3.5 million in a single-phase project to enclose the lower portion of the structure and address issues with corroded steel and cracked concrete.
The council could choose a cheaper option of leaving the lower levels exposed, which would cost $3 million if spread over multiple phases or $2.7 million if completed at once.
If the council opts not to address the main structural issues, the city still would need to spend $1.6 million on basic maintenance and repairs to keep the tower in operation. Eventually, the assessment says, these maintenance measures could become too costly, creating a need for the tower to be taken down. Dismantling and removal of the structure -- ending use of the 72 bells of the Millennium Carillon -- is included in the $1.6 million estimate.
Officials said city council members have been made aware that the Moser Tower assessment is complete. But they'll wait their turn to begin an official review of the results.
The document will come for council review after it's discussed by the planning, design and construction committee of the Riverwalk Commission and after the full commission forms a recommendation, Erickson said.