The most complex heritage retention job we have seen in Toronto in recent years has become more of a structural marvel in recent months. Found on the northeast corner of University Avenue and Dundas Street West, the site will one day be the home of the 52-storey United BLDG, but before that can happen, four levels of earth need to be excavated out from below the previous buildings onsite — all while their heritage features are retained with the help of an intricate steel support system.
The Davpart project is designed by B+H Architects, but has also tapped ERA Architects to assist in this technical heritage conservation effort. Part of what’s so amazing about the process is that, for the most part, the support system is located behind the streetwall, rather than being on display in the public realm, so in order to really understand how this system is working, we need to see it from the back.
Looking southwest in the image below, we can see the C-shaped outline that the retained elements form around the site’s four street frontages. Both the classical modern volume (west, at right) and the Beaux-Arts volume (east, at left) were components of the Maclean-Hunter Building, which was the headquarters of Maclean Publishing for most of the 20th century. The retention system is affixed to these features by steel framing connected to portions of each original floor slab, which creates a robust grid of structural steel on the backside of the streetwall.
At grade level and just below grade is where things really get tricky though. The load from each facade and the remaining floor slabs is distributed onto a layered truss system, pictured in the image below, that rests upon a series of piles bored deep into the ground. The vertical/angled trusses work in three dimensions, branching out from the various nodes to establish three points of contact with the horizontal trusses, which then employ a similar configuration of steel to transfer that load down to the piles. We can also see that long-spanning corner reinforcements are being used to tie the retained features together, adding greater lateral stability.
With this system in place, excavation work has picked up, carving out what will eventually be a four-storey below grade parking garage where there was only a single below-ground level before. Looking at the site’s northeast corner in the image below, we can see that a depth of about one-and-a-half storeys has been reached, suggesting that the project is approaching the halfway mark of its excavation journey.
Stepping out to the south elevation, the retained features fronting Dundas Street West offers a glimpse of the future pedestrian arcade that will enliven the building’s ground floor experience. The slab dividing the space horizontally is set to be removed, and the full height of the first two levels will be devoted to an open air walkway framed by the tall arched openings.
With excavation advancing steadily, forming could be underway before the end of the year, allowing work to begin on bringing the huge podium and eventual 52-storey tower. In its entirety, the project will deliver 709 new units while also offering commercial office space and grade level retail.
UrbanToronto will continue to follow progress on this development, but in the meantime, you can learn more about it from our Database file, linked below. If you'd like, you can join in on the conversation in the associated Project Forum thread or leave a comment in the space provided on this page.
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