Structural Engineering Award of Excellence: The Residences of 488 University Avenue, Toronto

David Liang
Senior Engineer
Sigmund Soudack & Associates Inc., Toronto

Presenter to be confirmed

An Inventive Solution Incorporates an Existing Building

Located in Toronto’s center atop an existing 18-story office building, 488 University Avenue was initiated when the site’s owner realized it was zoned for 57-story high projects by the City of Toronto. However, the government did not allow for the demolition of the office building due to the employment protection requirement. The owner came up with an ambitious idea that would allow them to expand the building to its maximum height while keeping the office in operation. A braced tubular exoskeleton form was proposed to support the additional 37 stories. This tubular structure would provide strength and stiffness to protect the existing office building, which hosted the United States Consulate General office on the sixth floor. To accommodate additional parking spaces, a top-down construction approach was implemented to create four more parking levels and place the new foundation on top of sound rock.

Existing building caissons were exposed and worked as columns for the new parking slab and basement perimeter walls were constructed in a panel-by-panel underpinning approach without an external shoring system. A tunnel was created to connect a TTC underground subway station to the P2 level, and also provides it with direct access to public transit. Two 800-milimeter-thick new tower load-bearing shear walls were built inside existing building mechanical shafts, located at the center of the existing building and each carrying 55 percent of the new tower loads. Slip joints were used to tie the tubular exoskeleton and new interior shear walls to the existing building structure, adding stability and avoiding the transfer of new tower loads to the old structure. A thick concrete slab of 350 millimeters was added on top of the existing building’s roof, supporting the concrete placement for the transfer beams. Due to limited existing roof load carrying capacity, two layers, bonded with a Sika bonding agent, comprised the concrete slab.

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