WINDS WALLOP ALBERTA
Tricia Wensley braves the elements with her umbrella as rain and high winds battered the region Wednesday. Environment Canada reported gusts as high as 85 km/h at the airport.
No matter how much planning is put in place ahead of time, once Mother Nature gets angry, you’re out of luck.
That’s what the city of Calgary found out today, when the rain came down and the wind howled, and the removal of the 12th Street bridge in the southeast was delayed.
The bridge, which spans the Bow River on the south side of St. George’s Island, is being replaced due to its age and deteriorated condition.
It was constructed in 1908 and was intended to carry horse and buggy traffic along with pedestrians to the island. It’s now used by vehicles, bikes and pedestrians as an important link to the island.
So how does one go about moving a 109-year-old bridge?
For starters, the foundation needs to be intact.
After the 2013 flood, the city had divers do an underwater survey of the foundation. The original plan was to have the old bridge remain in place while the new one was being constructed. The flood, in combination with traffic and other harsh weather conditions, made the case for an early removal of the bridge.
A 3-D model of the bridge was made to figure out how it would behave when moving it.
The project manager, Katherine Hikita said they weighed different options on how to remove the bridge. One option was to have something underneath the bridge, dropping it and then pulling it out of the water.
They also considered cutting it up into pieces but axed that option as the whole structure would come apart. There’s also a high concentration of lead in the paint, which means there needs to be a controlled removal to minimize environmental impact.
Next, the team took off the deck of the bridge to look at the condition of what was covered underneath and then adjusted their models accordingly.
With months of planning, the team is well prepared and has thought about all sorts of scenarios. If something were to go wrong, they would adjust accordingly and move forward.
“If something were to come up, it would be an unknown unknown, things we haven’t thought of, you know, UFOs, aliens, that kind of thing,” said Hikita.
The project team settled on using a crane to lift the trusses, bring it around in a semicircle and place it onto St. George’s Island for dismantling. The process is expected to last 20-40 minutes.
The bridge itself is 75 metres long, six metres wide and nine metres tall and weighs an estimated 90 tonnes. The crane can lift 650 tonnes, so there’s a decent ratio that makes for safe lifting.
Weather permitting, the plan is to remove the bridge by the end of the week.
The new bridge will open in late 2017.