By Moffette Tharpe, Robert Bouchard, CPCI,
and Michael Chusid, RA, FCSI
Montreal’s Hilton Garden Inn—a hotel and residential structure—has 43 floors—37 above-grade and six below-grade parking levels. With 216 hotel rooms and 211 apartments, this $67-million project was designed by local firm, Geiger+Huot Architects.
According to firm principal Eric Huot, MOAQ, MOAA, the choice to use studcast panels was driven by cost and logistical limitations. The team was committed to using precast panels from the beginning. As design evolved, it became evident conventional precast panels on the upper storeys would present problems.
“We had certain issues with the reach of our crane that would limit us to single panels (3 x 3 m [10 x 10 ft]) on the upper floors, instead of larger sizes,” says Huot. “That increases the number of installations—it would have been prohibitively expensive.”
The studcast panels provided significant savings, achieved by reducing the number of panels and lightening dead load on the structure. In some locations, mostly near the base of the structure, conventional heavy precast panels were used for specific logistical and structural needs. For example, panels near the ground floor had granite veneers cast into them, and it was felt a thicker panel would hold the stone better. Thick panels were also used beneath windows, where the window units rest on the curtain wall panel. Of the 10,680 m2 (115,000 sf) of panels cast, less than 20 per cent were conventional thick panels.
Huot notes the only difference in designing using studcast was in the detailing of connections.
“In visual terms, the studcast and the conventional panels look the same,” he explains. “We got exactly the look we wanted.”
Since studcast was new to the architect and contractor, a mockup of one full bay was constructed to test colour, jointing, thermal properties, and other considerations. The mockup enabled them to better understand the process and identify any special challenges.
Adjustments to the standard system related to the region’s potential for extreme temperature shifts—as much as 20 C (36 F) during the course of a single day. Urethane insulation was sprayed into the wall cavities, and the mockup helped work out the protocol for making sure the insulation penetrated fully into the air gap between stud framing and concrete.
The precaster cast many two-colour panels: light beige, with both heavy and light sandblasts, and black-pigmented with acid wash. Some of the panels included very large openings. Using a proprietary process, panels were made featuring curved surfaces on two sides of the building. They also created a special black joint sealant to blend with the black concrete.
During the 36-month construction schedule, panel erection took place over about six months. There was a strong desire to finish the hotel portion of the structure—the lower 14 floors—as soon as possible. After they were enclosed, there was a delay of about four months while structural concrete was placed and cured before cladding could be installed on the upper storeys.
Sylvain Paquin, civil engineer and project manager for general contractor Groupe Canvar, says the panel installation was significantly faster than erection of conventional precast panels.
“With regular precast, we can install eight to 11 panels per day,” he explains. “With the studcast panels—15 to 20.”
Paquin’s team was able to land the panels in position and disconnect the crane quickly. With conventional precast, the crane would have to wait and support the panel during the entire welding process.
For more on thin precast/steel stud hybrids, click here.