With fall creeping in and another month of construction flying by, the time has come for another update on progress at one of Toronto’s hottest projects, the reigning UrbanToronto Forum headliner, The One. From Mizrahi Developments, the ambitious project has been moving along month by month on its way to becoming the tallest building in Canada, and the first super-tall tower this country has seen. But beyond the hype surrounding the building’s impressive height — tentatively slated at 338m pending new approvals from the City — the design by Foster + Partners has garnered attention for its column-free Apple Store floor plan and striking structural exterior.
In previous months, we have looked closely at the innovative construction systems that have enabled the construction of the highly engineered building, and examined the various finishings that have been introduced at the pedestrian level up to this point. This month, we will be focussing on one of the few aspects of The One we haven’t covered yet, an element that is both central to the design and the structural hierarchy of the tower: the corner hangers.
Looking at the renderings of the completed tower, the corner hangers are the diagonal steel braces, clad in development’s signature champagne bronze metal finish, that appear in repeating sections on all four elevations, meeting at the corners of the building at a V point. Adding a distinct visual character to the massing of The One, the hangers also play a role that is integral to the building’s structural viability, allowing the weight of the floor plate of each corner to be redistributed to the tower’s eight super-columns.
Different aerial images captured throughout the construction process, like the above image by UT Forum contributor noggnogg, show the cruciform character of the floor plates that are installed through the use of the Automated Climbing System (ACS). The tower has progressed this way because of the locality of the super-columns, residing not in the corners, but closer to the centre of each elevation. In this way, a structural element needs to be installed to support the corners of each floor plate, and the hangers are able to accomplish this effectively through the use of tension. Each hanger connects to the outer super-column of two adjacent elevations, and with each corner hung, the downward force of the plate is directed right back into the columns rather than relying on support from the foundation.
The hangers appear every six storeys to bear the load of six corner plates at a time, securing them all from the hanger’s corner point at the lowest level. How the hanger supports the next five floors all from the bottom point can be seen in the rendering above, with the use of slender concrete columns in each corner. Interestingly, a column is not required on the top floor of the six-floor section, because the floor above it will always be supported by the next hanger.
UT Forum contributor Benito has consistently monitored the construction of the One, and captured the early stages of installation of the building’s first hanger in the southwest corner. The image above, from March 24th, shows the steel hanger bolted into the super columns at two points, and the concrete forms for the corner plates of the tower’s third and fourth storeys being installed. One point to note here is that this first hanger is the same height as the rest, but will only support three floors because of the double height of those three subsequent floors above the 40-foot grade level.
Fast forwarding to September, a street level image captured last Tuesday by UT Forum contributor Riseth, shows how far the hangers have come since then. The first row of hangers have been installed at all four corners, and the three plates at each corner have been formed and poured. Looking above the completed section at the northeast corner, another hanger has been bolted into the super-columns, and the form for the first of six corner plates is in place along with the rebar for the concrete column at the plate’s corner.
Another image from Benito, captured on Friday, takes us above ground with an east facing view to examine the west side of the building. The zoomed in image shows us that the hanger in the southwest corner has also been installed, and the lowest of the six corner plates has been fully poured. The concrete column is also completed in preparation for the next floor, but no form is in place yet.
The installation of the corner hangers is directly dependent on the height of the super-columns. Too much tension pulling on the columns from the corners could pull them right down, so naturally, the corners have been advancing at a slower rate. As the rate of completion of new floors continues to improve, the same should be expected of the corner plates.
UrbanToronto will continue to follow updates for this development, but in the meantime, you can learn more from our Database file for the project, 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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