March 24, 2016
by David Steiner
Housing the headquarters of developer Allied Properties REIT along with tenant spaces, the new building is supported by sculpted steel columns within the atrium as well as by concrete columns buried inside an existing building.
CASTLE IN THE SKY
PROJECT Queen Richmond Centre West, Toronto, Ontario
ARCHITECT Sweeny&Co Architects
TEXT David Steiner
PHOTOS Doublespace Photography unless otherwise noted
Richmond Street runs west through the centre of downtown Toronto. When it passes Peter Street, it pulls slightly south, then straightens. This jog in the road gives drivers the impression that they’re heading directly for the lobby of the new Queen Richmond Centre West,
developed by Allied Properties REIT and designed by architecture firm Sweeny&Co. That kink in Richmond Street—and the way the view ends at a century-old brick warehouse—created an opportunity to construct an iconic commercial building.
A client who wants to build an icon is often hard to please. In this case, however, the architects and Allied president Michael Emory shared a clear and simple idea of what the finished result would be. They wanted to preserve two existing brick buildings set at right angles to each other and imagined a new office tower perched above, starting 24 metres in the air. The office tower would be built with exposed concrete, which is as close as you get in new construction to Allied’s brand of brick-and-beam buildings, meant to attract those who value the texture of exposed wood structure and masonry walls.
Three bundles of steel-and-concrete columns, which the project team calls “delta frames” for their triangular geometry, support the majority of the load from the tower above. An intense engineering process led to the development of the cast steel nodes that elegantly connect the upper and lower legs.
To carry a concrete building, the team designed a massive tabletop for it to rest on. Supporting the table top are three giant steel columns, coming down through the atrium, and eight additional concrete columns, buried inside one of the historic buildings. The elevator core provides additional support. The twenty-metre-high L-shaped atrium replaces what used to be surface parking. At its two ends, the atrium is capped with structural glazing, suspended from the edge of the tabletop above.
Many parts of the design are good commercial practice—the raised flooring throughout the tower, for instance, which incorporates displacement air vents, and a negative pressure core that draws air out of all tenant spaces without the need for ductwork. Moveable light shelves on the south, west and east façades are connected to the building automation system, reflecting sunlight off the underside of the slab and deeper into the floor plate. These interior details come standard with the “core and shell” of the building for all tenants, dramatically reducing energy consumption and making office workers more comfortable.
Other parts of the design are strategic. The oversized elevator core has the capacity to serve a future development planned for a parcel of land immediately to the north, also owned by Allied. Then there’s the martini bar poking into the atrium, set on top of the loading dock. It was decided to add it in near the end of construction, in what was a leftover space. There is no parking, despite 30,000 square metres of office space—instead, the developer has struck an arrangement with the city to use a nearby parking structure that they own.
But it’s those three columns in the atrium that make this building a thrill to enter and an icon for Toronto.
The slender columns soar five storeys above visitors in the semi-public atrium, supporting the tabletop base of the tower above. A minimalist glass curtain wall is hung from the structure overhead.
Stephenson Engineering, which led the structural design, calls them “delta frames,” and they support close to three-quarters of the gravity load from the tower above. All three are essentially the same: made of eight steel legs, each a metre in diameter with 50-millimetre-thick walls. These are filled to the top with concrete, pumped in through a hole at the bottom of each leg. A large steel plate at the base of every leg, hidden under the tapered column end, bears on the corners of a 1.8–metre-thick concrete slab, carried to bedrock by caissons. The top of every steel leg aligns with a concrete column in the tower above. The upper and lower legs connect
at a cast steel node. Speaking with the architects, owner and engineers, the magic of this project resides in these three nodes, one in each frame.
During development, the difficulty in resolving the connection of the legs was both structural and aesthetic. Slender columns require bracing that can look bulky and cluttered. Dermot Sweeny, MRAIC, principal of Sweeny&Co, said he wanted the legs to just “kiss” one another at the joint, but the fabricator’s solution at the time was a big steel plate, welded on site, to join the legs. The practical requirements of welding such a plate pushed the legs out from one another, reducing the stiffness of the connection. It also meant the stair and elevator cores would grow in size to take more lateral load. Cast Connex, a Toronto engineering firm specializing in steel castings, was hired on a design assist contract to develop custom cast nodes. Cast steel made the joints stiffer (the amount of material buried inside the hollow castings increases the surface area the load travels through) and allowed the exterior forms to be graceful. Each node binds the legs together and transfers load through the frame, without compromising the impression that the column is made from four bent rods, lightly touching at the middle.
A cast steel connecting node is removed from its sand mould. (Photo: Cast Connex)
Because this kind of large-scale, custom structure is relatively rare in Toronto architecture, it’s worth noting the process that went into constructing these nodes. Cast Connex worked with Stephenson and Sweeny&Co to find the correct exterior geometry, and then shaped the interior to support the loads involved. This entailed detailed digital models tested through finite-element numerical analysis—essentially taking the node’s complex geometry and chopping it up into tiny squares that are mathematically examined for structural ability.
Excess flashing material is ground away from the node. (Photo: Cast Connex)
Though the loads are different in each delta-column, the node is the same in all three, designed to accommodate the largest forces. The fabricator (a foundry in Kansas) made a 24-piece, CNC-cut wood block of the node’s negative shape and filled it with a sand-slurry mixture that cured into a mould or “tool.” To create each cast, twenty-three tonnes of chemically tested recycled steel was poured into the tool in a sixty-second operation; the cast was then cooled for a week, heat treated, tested through non-destructive examination, heat treated again and finished.
The node is lowered by crane and temporarily fastened into place at the junction of the steel columns. (Photo: Cast Connex)
All parties commented on the cost involved in the design and construction of the delta frames, but acknowledged that the investment paid off through a fully leased tower. Also, they noted that the simplified and rapid process of steel erection—along with the leaner stair and elevator cores involved—made the investment comparable to more conventional fabrication methods. Allied’s Michael Emory said it was a struggle to sell the building’s image on paper to early tenants, but once the delta frames were erected, the remaining vacancies disappeared. Companies could see that something unique was underway and wanted in.
Allied Properties oversaw a highly integrated procurement process, where all parties shared design information as it was being developed. This was a calculated risk to build something complex and unique. When a developer wants to invest in the research and development
of custom building components, it is evidence of a healthy relationship between architecture and business. The old adage holds: good design is good business.
David Steiner is a freelance writer living in Toronto. He writes about architecture and design for a number of national publications.