Rusting zoo bridge will be demolished after giant crane removes it from perch

The City of Calgary says rust is eating away at the underside of the zoo bridge. But it has also revealed the span will be getting a memorable send-off.

'It's going to be an exciting event,' city engineer says

Roughly 8,000 people cross the 12th Street S.E. bridge daily, according the city's 2012 data. (City of Calgary)

The City of Calgary says rust is eating away at the underside of the zoo bridge. But it has also revealed the span will be getting a memorable send-off.

Last week, the city announced that the bridge on 12th Street S.E., which links the zoo and Inglewood, will be closed and removed a year ahead of schedule.

A structural engineer with the city said an inspection done in November on the span, which dates back to 1908, found corrosion is a growing problem.

"Inspectors were able to really get at the underside of the bridge and hammer at it to determine the level of corrosion," said Katherine Hikita.

"We found that some of the critical [support] members on the underside of the bridge have suffered more corrosion than our previous reports had detailed," she said.

Outside factors a concern

Katherine Hikita is the 12th Street S.E. bridge replacement project manager. (CBC)

Hikita said it doesn't mean there's any immediate threat to the span, but there are concerns that outside factors like flooding or ice jams could make the bridge more vulnerable to failure.

The bridge was closed to regular traffic two months ago. Only pedestrians are allowed to use the crossing.

Removing the bridge will actually be linked with the construction of the new bridge, now underway just to the west of the historic span.

Hikita said a large crane that will be used to place girders for the new bridge will help remove the old bridge.

"We're ... looking at picking it up from where its current supports are with a large crane and placing it down on the north riverbank," said Hikita.

Lead paint another problem

The asphalt on the bridge deck and other material will be removed before the crane swings into action. As well, the bridge will be reinforced prior to removal to ensure it does safely go in one piece.

The trusses on the top side of the bridge are covered with lead paint, which is a hazardous material. So once it's safely on St. George's Island, she said work crews will use special equipment to snip it apart to prevent any contamination.

Portions of the bridge will be used in a commemoration of the span — and possibly in the public art which will be placed at the site sometime in 2018.

'Exciting event'

Hikita expects removing a bridge could attract a bit of public interest.

"We are planning on doing some time-lapse photography and we are anticipating a crowd to come out and watch it. It's going to be quite an exciting event," said Hikita.

A date for the removal will be set later this spring.

Artist rendering of the 12th Street S.E. bridge replacement (City of Calgary)

The city has said it will give two weeks' notice of the bridge's permanent closure. It's not known how much preparation time will be needed for the removal operation, but that notice will give Calgarians a chance to go for that last stroll.

The new 12th Street bridge is expected to open by the end of this year.

The total budget for the new bridge and the removal of the old span is $26 million.