As the tower floors were initially meant to house sport gyms, massive concrete panels were installed along the outside of the tower structure during construction, only allowing for smaller windows at the top of each floor to provide natural lighting that would allow practicing different sports without the blinding effects of excessive sun glare.

As modern office spaces are usually flooded with natural light, replacing the concrete panels with a glass curtain wall was the logical choice. The regeneration of the space would also involve a thorough update of all electrical and mechanical systems while the interior would require a complete overhaul including the entry hall, new elevators and other facilities.

Assessing 30-Year-Old Concrete Walls

But that wasn't all – the tower’s 1.2-metre thick concrete shell would require examining to assess how permeable it was to humidity and cold, and how it would interact with a fitted-out and fully air-conditioned interior.

WSP’s building science experts came to the rescue, conducting detailed assessments to determine the need for additional insulation for the concrete walls and for treatment of the external membrane. This was needed to ensure that once the building was up and running there would be no consequences on the tower's envelope and interior. The assessment was done by taking concrete samples from various parts of the structure and studying their characteristics.

Over several years, WSP has worked on various projects at the stadium and, as a result, our engineers have become well-acquainted with the stadium and the tower’s complex and unusual structure.

“This is not a standard building, so it takes a certain time and experience to fully understand the design philosophy and the intricate structure of the stadium complex. Having worked on multiple projects at the stadium since the 1990s, our team had gained a deep understanding of it,” said Pierre Rodrigue, lead designer on the project and Head of the Scenography Team at WSP’s Montreal office.

Our team was selected to provide structural engineering on the project as well as the 3D scanning and creation of a complex model of the tower using Revit.

The first task for our engineers was to figure out how to install two enormous cranes needed for the construction. At more than 200 metres, the main crane “The Giraffe” is one of the tallest tower cranes ever used in Canada. Two additional cranes were used to put together this giant.

“The Giraffe” needed to be close enough to the tower but, at the same time, remain at a safe distance from the top of the inclined tower and the cables supporting the roof. As a result, it was installed within the stadium which meant piercing through the existing stadium roof made of a metal structure, a flexible roof fabric, and two floor slabs. The crane was installed on a concrete base anchored in bedrock. Two bracing beams attached the crane to the stadium’s base with two more connecting it with the tower near its top to ensure stability.  

The other smaller crane was installed on the back of the tower sitting atop the inclined surface of the lower funicular station roof, which functioned without disruption during the whole construction process.

Removing massive concrete panels was one of the most difficult steps of the project. Due to the tower’s complex geometry, curved both vertically and horizontally, all panels had different shapes and weighed up to five tons each. Tests were undertaken to better understand how it could be done, considering the sensitive positioning of the panels, some of which were situated above the sports centre while others sat above the stadium roof. The results of the tests were used to guide and support the contractor.

Replacing the concrete panels with a glass curtain wall while retaining the same curved form would have been very costly and, in the long run, would imply a significant risk in terms of potential problems with weather tightness of the facade. Consequently, the decision was made to eliminate the horizontal curve of the tower to simplify the new facade, while respecting the original architecture.

Our structural engineers designed slab extensions for each floor, which turned out to be quite a task due to the building’s complex angles and the different dimensions and form of each slab. A 3D BIM model was used to make calculations and design a secondary steel structure to support the curtain wall as well as for the construction of slab extensions. Once the design was completed, our team closely monitored the construction process.

Project deadlines were also quite stringent: our work on the project started in the spring of 2015 and finished in November 2017. The result, however, is impressive.  The new facade complements and enhances the existing iconic architecture while letting loads of natural light inside the new office space. On the outside, depending on the time of the day and weather, the new facade either reflects the sky or exposes the tower’s complex structural elements.

The tower revitalization project will bring more than 1,000 employees to the area on a daily basis, potentially enhancing the vibrancy and the local economy of the neighbourhood.