A downtown Portland parking garage will close for at least four months after maintenance workers found damaged concrete.

The damage to the city-owned O'Bryant Square SmartPark garage, located near Southwest Stark Street and 9th Avenue, was discovered during a planned repair project. There's a risk pieces of concrete could fall and injure people or damage property.

The garage will close effective Monday. The O'Bryant Square structure isn't open on weekends.

The Portland Bureau of Transportation believes the structure is safe to use Thursday and Friday, spokesman Dylan Rivera said in an email. The risk of falling concrete, however, will increase during rainy weather.

"We do want to provide some notice to the public in advance of this closure," Rivera said. "If we thought there was an imminent threat to safety, of course we would close it immediately."

O'Bryant Square Park, which is at ground level above the parking structure, is unaffected by the closure. The bureau said there is not believed to be any risk to users of the park.

A structural engineering firm will assess the damage and provide repair options, a process that could take as long as four months, the bureau said.

The garage and park opened in 1973.

-- Elliot Njus