Designing for Constructability Over Active Rail Lines
Ian Washbrook is a Principal at Entuitive based out of our Calgary office. He led Entuitive’s structural engineering efforts to help transform Calgary’s East Village neighborhood, first with the New Central Library and then with the Platform Innovation Centre & Parkade. We recently sat down with Ian to discuss how Entuitive’s structural consulting services contributed to the constructability of these landmark projects.
Tell us about these projects, specifically the constructability role on both?
Entuitive served as structural engineering consultants on both the New Central Library and the Platform Innovation Centre & Parkade. Our constructability related efforts at both the Library and Platform were similar in that we didn’t package up the construction engineering work as a service offering. These projects pre-date Entuitive formalizing construction engineering as a service and our acquisition of Brown & Co. That said, structural engineers are responsible for ensuring a building or project is ultimately constructable.
What were the construction engineering challenges you faced on each project and how did you solve them?
Building Over an Active LRT Line
Platform is across the street from the New Central Library, and both presented the same main challenge – building over an active light rail transit (LRT) line. The only difference was that at the New Central Library, we had to design a tunnel extension as it didn’t exist at the time, while for Platform, the tunnel already existed. Although a tunnel existed at Platform, it was load restricted which impacted heavy construction activities.
When Entuitive pursued the Platform project during the RFP process, we certainly leveraged our current and relevant experience of designing a building overtop of an active transportation corridor at New Central. This was also demonstrated during our interview and was likely one of the factors that helped us secure the Platform project.
To build over the active train corridor the superstructure framing of both projects required long span truss solutions. In the case of Platform, there was also a utility corridor consisting of a 30” diameter main water line under high pressure right next to the train line. This meant that even longer trusses were required to span over both below grade infrastructure pieces. These trusses support significant loads from the six levels of relatively heavy concrete framing in addition to the self-weight of parked vehicles.
Assembling each truss horizontally on the ground and lifting it into place would have required very large, expensive, and heavy mobile cranes which would have exceeded the existing tunnel infrastructure load restrictions. The solution, which was identified early in the design phase, was to assemble the trusses in mid-air. Concrete for the slab infills was installed after the trusses were self-supporting. This is like the solution we employed at New Central Library.
Implementing this solution required a detailed and elaborate sequencing methodology. We proposed construction sequencing that ended up being a twenty step, concise table, which was included in our drawings as a suggested means of construction. The table indicated how we assumed the building would be constructed. We weren’t retained for the actual sequence because we weren’t formally offering construction engineering as a service at that time so we couldn’t assume the liability.
The construction sequence that the construction manager, EllisDon, and the steel trade contractor, Supermétal, followed essentially mirrored our suggested sequence outlined in that very concise but detailed table in our design documents.
Coordinating with Calgary Transit
Both projects required coordinating with and obtaining confidence from Calgary Transit, who were involved throughout most of the milestone steps to ensure we weren’t imposing additional loads. In the case of Platform, we had the additional challenge of ensuring we didn’t expose the tunnel or disturb the day-to-day operations of the train service.
How did we add value to the trade contractors and construction manager?
Our early identification of a construction sequence was the most valuable contribution we made in terms of construction engineering for both projects. There were so many steps that needed to be followed in the right order for the projects to come together successfully. Our critical thinking on how to put these together is our biggest contribution to the steel fabricator and erector, along with the construction manager.
Early Involvement and Constructability
We were involved very early on in the design phase, which meant our constructability advice was highly useful to the team. For instance, we were able to think ahead of the construction manager in the case of the library where the biggest truss weighed 500,000 pounds. We knew temporary shoring posts would be needed underneath the nodes where the diagonal webs hit the chords. From the first instance of the piling contract (two years before the building was constructed) we suggested designing piles underneath each one of the nodes because the temporary shoring post loads were so high. These piles were installed very early on, over one year before the steel fabricator was onboarded.
The construction manager, Stuart Olson, agreed with our idea to use the piles. It worked so well that it became a non-issue. If we hadn’t thought of that, they would have had to create a large temporary foundation system that would have been more complicated and more costly. In that case, the system would have settled and there would have been a need for more jacking and other supports over time. In fact, we probably would have regretted not putting in piles when we had the chance to.
We worked with the same steel fabricator and construction manager on both projects. We advocated hard to have Supermétal, the steel fabricator, come on early in the process in both cases but especially in the case of Platform. We did this because it’s important to have an experienced trade contractor who can think about things like scheduling, material waste, etc. and who knows the “lay of the land”.
With the library we worked as a team with linear communication where the construction manager, Stuart Olson, served as the intermediary (in other words we didn’t have direct conversations with the steel fabricator during the pre-construction stage). We improved upon this with Platform, where we were able to determine a triangular relationship and have larger constructability conversations earlier on. This is where we were able to define and hone our sequencing and it paid off. We worked to troubleshoot problems in advance before shop drawings were produced which saved us time. And our holistic thinking of the design and build process meant there were less problems because we were aligned on the strategy from the get-go. We kept on reverting back to the twenty-step process. Even when we deviated, we always came back to what worked.
The biggest benefit from this collaboration and our construction engineering solutions was how smoothly the projects ran. Of course, there are always little things you must solve along the way but overall, the process was smooth, on schedule, and on budget.
What has been your favourite part of each of these projects?
For me, it was the encapsulation phase at the library. Seeing it come together exactly how we planned it without any delays to the trains or any injury was rewarding. It was my first real infrastructure project, and it was unique in challenging my thinking on construction engineering and the sequence of building. There was also the enhanced element of safety – protecting the trains, riders, construction works, and surrounding people and infrastructure.
Another aspect was reducing service interruptions to minimize disruptions to Calgary Transit and its ridership during construction. The cost to shut down the train line for one day is close to $100,000 as busses need to be added to assist with the public’s transit needs. The last shutdown related to the encapsulation was to place the roof over top of the tunnel and this was completed in just over 24 hours, which was incredible. There’s a phenomenal time lapse of how the encapsulation occurred within the 24-hour period to finally become a tunnel.
Craig Dykers of Snohetta, the Managing Principal on the project who envisioned the design was blown away when he visited Calgary and walked on top of the tunnel. He noted that the tunnel itself was a form of architectural sculpture. It curved on a plan and sloped up. It was an elegant piece of concrete infrastructure and Craig’s comment was a high compliment to us.
With Platform, seeing those big mega trusses standing up in the air and self-supporting one another was rewarding. I’m sure most people walking or driving by didn’t understand why these massive structures were just standing there. I’m sure most people didn’t realize there was a tunnel underneath or what we were building. It’s cool to think we can have such a significant impact on infrastructure.
Any last thoughts?
The experience we derived from these two projects and the solutions we created can be applied to other projects in the future. Although each project has unique challenges, for complex infrastructure or steel projects especially it makes sense to engage the construction manager and have constructability discussions early on.
For example, right now we’re working on a Boeing 747 project where we’re engaged with a custom and creative fabricator and a steel fabricator. We’ve been joining them for weekly meetings for a year on constructability of the steel frame that supports the plane. Ultimately, the result was that everything came together perfectly. There were still RFIs to clarify dimensions and other aspects of the project but relatively very few.
I guess one final thought is that Entuitive loves thinking about and solving these types of complex construction engineering challenges. Everyone loves seeing the pyramids and, sure, they’re amazing wonders to view but what’s most fascinating for people, at least from my perspective, is how they’re built. I think it’s like the Platform Parkade – most people will never really know how it was built so it’s important to share these stories so people can understand how these projects come together. I’d also like people to understand that there are many creative minds that come together to make these projects happen. Our philosophy is to continue to learn from our past projects and to continue to innovate and find creative solutions to design more and more complex structures in the most efficient manner possible.
Thanks for sitting down with us today, Ian! We learned a lot.