The department of engineering plans to install a “catcher beam” underneath the Thunderbird (Fourth Avenue) Viaduct as a backup in case the existing bridge infrastructure fails.
Associated Engineering completed a preliminary design report in February as part of the City of Moose Jaw’s $16-million effort to rebuild the structure. That report identified a critical junction called a half-joint beneath the bridge — it connects the 1965 and 1989 sections — as an issue that needed to be addressed.
Installing a half-joint was a method used decades ago to connect two bridges with piers beneath them, where one span rested upon another, engineering director Bevan Harlton explained during the Sept. 27 regular council meeting. However, that type of connection provides a “big risk” since there is no backup redundancy if the structure collapses.
The catcher beam will sit below and catch the bridge if the half-joint fails, he continued. However, this addition does not extend the bridge’s service life since it’s not a part of the structure. Instead, it’s an additional layer of protection and gives city hall time to design and build a new structure.
The engineering department has issued a tender for contractors to build the catcher beam and conduct further deck testing. The tender closed Sept. 29 and the work is expected to begin in October.
The bridge will not be closed when contractors install the catcher beam, but it will be shuttered for a few days when engineers analyze the deck.
Funding exists in the 2021 budget to pay for this $230,000 catcher beam, Harlton’s report indicated. Meanwhile, a class B cost estimate for the Thunderbird rehabilitation — currently at 50 per cent of the design phase — is $16,041,850. This includes a 15-per-cent contingency and $2,991,850 in associated project risks.
As the design advances, the identified risks will either be addressed or added to the known costs, the report added. Meanwhile, funding for this project will be challenging, so the municipality will need support from provincial or federal grants and CP Rail.
If the bridge did fail and the catcher beam performed its job, then city hall would close the bridge immediately, Harlton added.
When council talks about supporting important infrastructure priorities, the Fourth Avenue bridge is one of the biggest, especially since it’s a major thoroughfare, said Acting Mayor Dawn Luhning. Meanwhile, council will have to come up with “creative ways” to complete this project since material costs will continue to increase.
“This is absolutely a priority. We need to take care of it right away,” agreed Coun. Crystal Froese. “We need to make sure there isn’t any unforeseen circumstances with that bridge.”
Another important aspect is that it will cost $16 million to rehabilitate the bridge, said Coun. Heather Eby. Before her time on council, she remembers how the city closed the bridge for a project and “it was a detrimental thing” for the people on South Hill.
“So, we want to be sure that this is something we get into our budget somehow sooner rather than later,” she added. “I know administration is working with CP Rail and will look at this during the budget. (Also), hopefully, we never have to use the catcher beam.”
The next regular council meeting is Tuesday, Oct. 12.
