Canadian Consulting Engineer

Feature

Remaking Simpson’s

In the last few years, Montreal's downtown corridor has enjoyed a renaissance of sorts. One notable project is the former Simpson's building, which stood abandoned since 1993 until Industrielle-Allian...




In the last few years, Montreal’s downtown corridor has enjoyed a renaissance of sorts. One notable project is the former Simpson’s building, which stood abandoned since 1993 until Industrielle-Alliance acquired the historic landmark in 1998. The developer’s goal was to transform the building into a $70-million glass-and-steel structure called Le Carrefour l’Industrielle-Alliance, which would house a Famous Players movie complex and IMAX theatre, a Simons department store and a food court.

There were, however, constraints that the project’s consulting engineers faced in the fast-track project, which ran between January 1998 and March 1999. “We weren’t allowed to modify the facade of the building for historic reasons,” says Gilles Deschnes, a structural engineer with Gnivar consultants in Hull, Quebec. “We had to keep the exterior of the building intact, while carrying out major structural renovations inside.”

The renovations (Desnoyers Mercure were the architect) included demolishing the fourth, fifth and seventh floors of the original eight-storey building to accommodate the movie theatres. The building dates from 1929 and had additions made to it in 1932 and 1959. The reconfigured building’s floor space is 305,000 square feet (28,334 m2), almost one-third less than the original 450,000 square feet.

The most challenging part was to remove about half the 100 columns between the third floor and the roof, so as to open the space for the 20-metre-high IMAX screen and 12 cinemas. The columns that remained had to rise six storeys in the IMAX sector, and three storeys high in the cinemas.

The engineers designed a system of supporting steel trusses that were used in pairs, the longest being 28 metres.The trusses were slid into place on each side of the column axis that needed modifications and were supported on each end on the columns that remained in place. The trusses were then loaded with a force equivalent to the dead weight and a portion of the live load that the remaining columns had to support. This loading was meant to act against the gravity and control vertical deflection when the undesired columns were cut and removed.

“There were not more than two that were the same,” explains Deschnes of the various columns that dotted the building. That was because the existing building was actually a combination of three buildings constructed next to each other in three different stages.”We therefore had about 40 different column case studies to consider. We had to consider the new loading patterns, the fact that some columns were unsupported for three to six storeys high, and the new loads to the foundations. In all cases it was necessary to avoid changing the footings because of the costs and need to respect the work schedule.

They used simulation software to model the columns, but the process was made more difficult because the engineers had to work without final plans during the project’s early stages. In effect, they had one or two cross-sectional views and a general view, and debugged the project as it went along. “We had to imagine what would happen inside once construction took place,” he said. “I knew that there were plans fox X number of cinemas and that large mechanical systems were involved.”

Working in a tight space

Such scenarios were common during the fast-paced project, in which engineers commonly put in 60-hour weeks. When it came to installing the 6.2-MW substation, for example, the electrical engineers worked out three different scenarios, including placing it on one of the upper floors. “That would have been a lot easier, but the building’s owners didn’t want to lose any rental space,” says Anthony Giday, an electrical engineer with Gnivar in Longueuil, Quebec. “So, we had to put it in the basement, which meant some structural work — excavating from the inside and stabilizing the foundations.” The power at entrance is 25 kilovolts, and it is stepped down to 600 volts, which powers three main feeder lines that run inside the building

At one point, given the demands made by the IMAX theatre — the screen’s height, size of projection and heating requirements — it didn’t seem as if all the components would fit together within a confined space, Deschnes notes. “We had to remove the roof and lift it by two feet. We were really tight and in certain areas we had only a couple of inches of give between two parallel walls.”

Keeping things cool

The project brought about some pleasant surprises, too. One of Gnivar’s engineers came up with a viable solution to a technical problem common to all Famous Players theatres across Canada, which is related to cooling the theatre’s laser-projection system. (The building houses a 600-ton cooling system.)

The heat exchanger failed to work efficiently using chilled water, a key design feature of the system. When it ran chilled water, it resulted in a 25-psi pressure drop across the heat exchanger’s surface. To compensate, the theatres operated the exchangers with a domestic water source. “Famous Players was never able to make it work properly,” says Christian Chu, a mechanical engineer with Gnivar in Longueuil.

That is, until Chu proposed a solution: (1) put a bypass on the supply and return line, which hydraulically isolates the two circuits; and (2) put in a three-stage boosting pump (5 US gallons per minute) on the secondary circuit to overcome the heat exchanger’s pressure drop, while keeping the total pressure to 75 psi — within the design limits of 80 psi. “The solution is still undergoing testing,” Chu says, “but it’s promising.”

The building’s design proves once again that engineering know-how can balance technical requirements competing in a fixed space. “The result is pretty impressive,” Giday says.CCE

Perry J. Greenbaum is a freelance writer based in Montreal.

Owner: Industrielle Alliance

Consulting engineers: Groupe-conseil Gnivar (Gilles Deschnes, ing. (structural), Anthony Giday, ing. (electrical), Christian Chu, ing. (mechanical))

Architect: Desnoyers Mercure