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. 

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