May 28, 2010

HALCROW YOLLES

A galvanized vertical truss is situated within the crown roof atop the tower at the Ritz-Carlton. The project garnered a Canadian Institute of Steel Construction award of excellence in the engineering category.

FEATURE | Steel

Puttin’ up the Ritz-Carlton not all glamour

PETER KENTER

correspondent

Beneath the elegant exterior of Toronto’s first five-star hotel, the Ritz-Carlton, lies a heart of steel.

The hotel and condominium sits on a five-level podium, with storeys six to 20 containing hotel rooms and guest facilities. Storeys 22 to 52 house condominium units and resident amenities.

Steel was a natural choice for the project’s structural engineers, Halcrow Yolles, who selected the material to support not only the building’s structure, but also because of its aesthetics.

The hotel’s base podium features an exterior made largely of glass supported by steel. The hotel entrance is protected by a cantilevered cover also supported by steel.

The building reflects the design elements of its neighbour across the street, Roy Thomson Hall. At the hotel’s twenty-sixth floor, the south wall of the tower begins to slope outward, complementing the curved exterior of the concert hall.

Steel helped to support the hotel’s luxury amenities, including a 24- by 31-metre ballroom on the third floor. The floor of the ballroom was designed as a column-free space.

The floor above the main ballroom includes executive offices and a junior ballroom, while the fifth floor features a fitness centre and spa. The structural support for the area needed to be stiff enough to mitigate human-induced vibration, particularly to adjacent spas and meeting rooms, but light enough to avoid overloading a concrete plinth below.

“Human-induced vibration is typically a structural concern in ballroom structures where activities such as traditional dancing and day events with aerobic activity have the potential to create vibrations that can be perceived by patrons,” says Howard Jung, a structural engineer with Halcrow Yolles. “A vibration assessment was carried out and it was determined that storey-high trusses were required to mitigate human-induced vibration.”

A pair of five-metre trusses spanning 24 metres in a north-south orientation above the main ballroom were fabricated, providing the global podium structure underneath with the stiffness required to resist vibration. The trusses were designed with irregular web member layouts to accommodate the doors to the meeting rooms on the fourth floor.

The downtown location is subject to consistently heavy traffic and offers little room for a staging area.

The decision was made to divert traffic north of the site for a weekend so the long-span members, trusses and girders could be lifted by mobile crane directly from a delivery truck into place on the podium.

“The storey-high trusses were fabricated in components and shipped to a large lot leased by the steel fabricator along Cherry Street,” says Jung. “Two steel trusses weighing approximately 50 tonnes each were delivered to the site on a Saturday, requiring police escorts and closure of Lakeshore Boulevard, York Street and Wellington Avenue.”

Once primary framing was complete, general contractor EllisDon was able to allocate a much smaller space to stage the remaining structural steel elements.

The building envelope is drawn inwards by two metres on the fifth floor, creating a terrace with a steel-supported cantilevered roof. The structure was designed using custom plate girders and steel also supports an east-west cantilevered canopy running the full length of the building, with the metal chosen to withstand accumulated snow loads.

A wind tunnel test was also undertaken to ensure the canopy could withstand area downdrafts. Structural steel used on the building totals approximately 400 metric tonnes for the ballroom structure and 215 metric tonnes for the crown structure.

Jung says he hasn’t yet had the opportunity to enjoy the hospitality of the completed hotel.

“Unfortunately, a structural engineers’ salary typically limits one’s ability to experience five-star dining,” he says.

Project developers were Graywood Developments and Cadillac Fairview. The architect was IBI/Page & Steele and concept architect was Kohn Pederson Fox.

The steel erector was Hillsdale Structures. The steel fabricator and detailer was C_Ore Metal Inc.

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