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With the first phase of CIBC SQUARE now occupied and active, the 49-storey office tower designed by WilkinsonEyre Architects and Adamson Associates Architects is asserting its role as one of the newest players to leave its mark on the skyline of Toronto. With its shimmering diamond-textured facade, the Hines and Ivanhoé Cambridge-developed tower is almost impossible to miss, but just in case there was any doubt of its landmark status, the developers planned a second phase tower, currently in the early stages of its skyscraping journey.
Located on the north side of the Union Station Rail Corridor, just across from its sibling tower, the second phase of CIBC SQUARE is nearly identical to the first in terms of its general appearance, but with a unique set of challenges associated with the site and its proximity to the active train station, innovation has been fundamental to the building’s ability to get off the ground. With the tower’s core now peeking out above the neighbouring station, we are taking a look at how it got to this point and how this challenging project will reach its 50-storey goal.
The root of the challenge for the construction of the second phase is the position of not one but two pieces of immovable transit infrastructure: the underground subway tunnels, and the above ground GO Train tracks. The GO tracks run literally beneath the footprint of the building — it will overhang the northernmost two tracks — meaning that any structural columns heading straight down for the south side of the building would be either on or in between active tracks.
Constructing the building that way was, therefore, not possible, so an alternative strategy was devised, with the help of consultants RJC Engineers, that would divert the load of the south side of tower back to the core, using a tension based steel bracing structure, ultimately avoiding interference with the tracks. A diagram of the structure is shown below in cross section drawings, with the steel structure represented by the diagonal lines forming a v-shape at the base of the building, its north side to be held aloft the same way.
12 steel nodes form the base of the bracing structure, providing connection points for steel beams that extend out to the edge of the building’s elevations. From there, another set of nodes are used to connect the steel beams, creating a plate of sorts, upon which the total load of the building will be laid and redistributed down to the core. The steel structure itself is shown isolated in another diagram below.
Looking at the work taking place on site in the early stages of the building’s core construction, we can report that the 12 nodes making the base of the steel brace were being installed throughout the summer. Now, in early December, we can see that the diagonal beams are beginning to emerge on the south side of the building, forming the early traces of the steel plate that will eventually wrap around all sides of the core, and trace the building’s total floor-plate.
To the east of the building’s core, extensive progress has been made in the excavated pit that will eventually become the tower’s parking garage and podium. Back in May, crews were working carefully to excavate the area without jeopardizing the south wall of the Dominion Public Building, a registered heritage structure.
With the excavation completed, work in the pit quickly transitioned towards concrete forming. The image below shows the state of the pit in late August, with rebar in place ahead of the concrete pour that would complete the lowest level of structural columns for the underground parking facility.
Jumping ahead to the end of November, the pit is hardly a pit anymore, with forming nearly reaching the ground level at the westernmost edge of the site. Meanwhile on the western side, closer to the core, several floors of scaffolding have been constructed around one of the five cranes, and concrete forms are in place to reinforce the southern shoring walls.
Finally, just beyond the eastern border of the site, work began in late October to get started on an external element of the project, building a new pedestrian bridge connecting the second phase via a new PATH bridge to Backstage Condos. To do that, the northern end of the Yonge Street tunnel under the rail corridor, unused by rail tracks, needed to be demolished. A new pedestrian bridge will be built crossing Yonge Street, much narrower than the section section, and will form a piece in extending Downtown Toronto's PATH section further east. A hallway within Backstage Condos' podium already exists, waiting to carry the weather protected pedestrian system to future projects.
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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