When the City of Calgary, Calgary Public Library and Calgary Municipal Land Corporation (CMLC) started talking about building a new central library, they shared a common objective—a strong civic library for Calgary that was connected to the city. They also knew they’d need to take a team approach to designing and building the facility.
“We selected the architect and prime design team by evaluating them to see if they’d fit within a team structure,” says Kate Thompson, vice-president of projects for CMLC. “We did the same when choosing the construction manager, and we chose them all at the same time so we had everyone around the table asking, ‘How do we build over a train?’”
Spanning two blocks in the city’s trendy East Village area, the $245-million library presented a unique challenge to the designers and construction team: it needed to be built over 150 metres of LRT line.
The first phase of the project, which is now complete, involved encapsulating an under- ground LRT that curves up a slope to the surface. While this posed numerous challenges, the biggest was probably that most of the work had to be done while trains were running. Keeping operators and passengers safe was a priority.
“In devising the structural scheme, we decided to separate construction activities and live LRT activities using the design. After the grade beams for the foundations were installed on each side of the existing line, we put up prefab panels that created a barrier. That precast wall ended up becoming the formwork for the actual structural wall,” explains Brock Schroeder, managing director of Entuitive, which is serving as a structural engineering consultant on the project.
The shape of the contact wire that powers the trains dictated the shape of the top of the encapsulation. The first step was to reconfigure the contact wire and take it off the poles that were supporting it, and then install new supporting beams. The wire was then enclosed using a precast double-T panel system, with the panels installed just inches above the contact wire to keep the encapsulation roof as low as possible.
Work had to be done when the power was off. To prevent disrupting train service, the original plan was to drop two or three panels into place each night when the LRT was not running. However, a planned 48-hour shutdown to work on LRT infrastructure presented the perfect opportunity to do the whole thing at once. The construction team worked 40 hours straight to get the 53 roof panels in place.
“The key to our success in doing that was a high level of planning, quality control and really competent trades,” Thompson says. “We had everyone around the table for months, starting from a high-level understanding of what we’re trying to do, right down to details as to how much time it would take to place each double-T, remobilize the crane and get ready to load the next one.”
Working with construction manager Stuart Olson, Entuitive choose the double-T precast panel system. The fact that only two of the 53 panels were identical due to the geometry of the site played a significant role in the decision.
“We chose the double-T because you could vary the shape and use the same forms for all of them. That meant there wasn’t a huge premium, even though each of the panels was unique in shape,” Schroeder says.
Entuitive used a similar system in an encapsulation project in Manhattan that involved 12-foot-deep panels encapsulating 13 rail lines, where the panels became a podium for four towers. Similarly, the encapsulation of the LRT line forms part of the foundation for the Calgary Central Library.
“We could have built the encapsulation as a purely temporary structure and then had a separate foundation system and floor system, but that means double the costs,” Schroeder says.
Using the encapsulation as part of the foundation meant that a number of big design decisions had to be made early on because there would be less leeway once the structure covering the LRT line was in place. The design team introduced as much flexibility as possible.
“From a design perspective, it was challenging. We completed the design of the encapsulation when library design was really only at the schematic stage,” says Ian Washbrook, project manager at Entuitive. “We had to really sharpen the pencil and make sure we weren’t under- or over-conservative with the loading assumptions.”
With the encapsulation complete, work has begun on the building itself. One of the most interesting aspects of the design is that the full building height acts as one massive truss to create the up-and-over walkway that joins the east and west sides of the building.
“The multiple storeys of the library have diagonal web members that form the big part of the truss that is both sides of the building. It’s quite exceptional, and I think people will truly understand it once they see it coming to life on site,” Thompson says.
The four mega-trusses are three-storeys deep (approximately 50 feet tall) and span up to 180 feet. The largest will weigh over 200 tonnes. Due to the weight, the web and chord members will have to be “stick framed” with each piece lifted individually and welded in the air.
“One of the nodes of the truss where the web member intersects with the chord member weighs 12 metric tonnes, and it’s a six-foot high by six-foot wide by 20-inches deep piece of solid steel,” Washbrook says.
As the building progresses toward its 2018 opening date, the construction team will face other challenges such as forming floors that have a gradual curve, installing the natural wood ceiling over the walkway and ensuring the project is completed to LEED Gold standards. But while the design has some complicated components, Thompson believes the project is very doable.
“There are other buildings that are much more complicated,” she says. “We wanted to choose a design that was as striking and beautiful as the city deserved but was also buildable.
Follow the project’s progress online at yycnewcentrallibrary.com/progress.