Construction of the 850-foot-tall, $570 million-to-$600 million Rainier Square Tower in Seattle is turning out to be a proving ground for innovation.
Aluminum components are being 3D printed with the resulting v-shaped nodes and connected squares of curtain wall forming a dramatic slope from the fourth to 40th floors. Aside from the impressive aesthetic, this method of production can also more easily accommodate last-minute changes.
Structurally, the high-rise’s design is being touted as a game changer.
Structural engineer Magnusson Klemencic Associates (MKA) started out planning to use a reinforced concrete core for the building, said firm CEO Ron Klemencic, “like the last 100 buildings we designed.” However, about halfway into the project, it was clear that the tower would be too expensive and was going to take too long to build, making it economically unfeasible for the building's owner, developer Wright Runstad & Co.
After tabling the project for about a year, Klemencic said the client asked the design and construction teams if they had any ideas that could jump-start the project without busting the budget, and the SpeedCore system, then just a rough concept of what was to come, won the development team over.
And so began MKA’s mission, in 2006 and 2007, to convert steel-plate composite-core technology that was being used in the defense and nuclear industries into a design that would work with high-rise construction. Purdue University assisted MKA as researchers there had experience with this type of construction.
“We went into the laboratory and started to test the performance of these panels in a high-rise scenario,” Klemencic said, “because the way the wall behaves (under those conditions) fundamentally is different than if it were a short, squat wall for a nuclear power plant, for instance.”
What resulted is a concrete-filled composite steel plate shear wall (CF-CPSW) core that starts with prefabricated panels made up of two structural steel plates held in place with cross-connecting tie rods. The tie rods, according to the American Institute of Steel Construction (AISC), support each panel before the concrete is poured during the erection process. The tie rods also place pressure on the concrete, which increases seismic performance.
'Speed is money'
Using this system, the AISC estimates that erection crews will be able to top out about 43% faster than if they had to build a traditional core. At the Rainier Tower Square project, using SpeedCore allowed crews to top out in 10 months, which was about half the time allotted in the original schedule, said Lawrence Kruth, AISC vice president of engineering and research.
The fast pace also allowed the owner to save more than $10 million, he said, when taking into consideration the reduced financing costs of a shorter construction period, decreased general conditions expenses and the ability to lease the building more quickly. The time-related savings, Kruth said, even offset the cost of using more steel, which the SpeedCore system requires.
“So, speed is a big difference,” he said, “but speed is money.”
However, in order to achieve that speed, said Leonard Joseph, principal in Thornton Tomasetti’s Los Angeles office, it’s important for the general contractor, fabricator and erector to develop a strategy and work together to overcome the learning curve quickly enough to realize the time savings that make spending the extra money on steel worth it.
“If by the top of the building they say, ’Now we know …’ that’s painful,” Joseph said. “If after the second or third story they say, ‘Now we know,’ then that’s great.”
In addition to the potential for a shorter timeline, the SpeedCore system offers other benefits as well:
- Strength. The concrete-filled prefabricated steel panels make for a robust structure, which is not surprising since the U.S. Department of Defense, Klemencic said, valued its blast protection qualities and the nuclear industry its resistance to projectiles.
- More flexibility for adaptive reuse. The SpeedCore system has no hidden rebar, making the structure more predictable during adaptive reuse projects.
- Safety. Because the progression of work on the system is so close to that of floor framing, much of the tasks take place under steel decking, meaning workers are protected from falling objects.
Overcoming the challenges
Despite the benefits and cost savings, there are some challenges that will have to be overcome if the SpeedCore system is ever going to catch hold industrywide.
One potential hurdle to the adoption of SpeedCore is the fact that there is no design manual and just one case study — Rainier Square Tower.
“Right now, you have to dig through the research … rather than following a method,” said Kruth.
However, the AISC is about 30% complete with a draft design guide, which might help encourage those on the fence about SpeedCore to test the waters. Also, the system is nonproprietary, which means fabricators are free to reproduce the system at will.
Once there are more SpeedCore projects completed, Klemencic said, that will take away much of the uncertainty about the system and provide others with a roadmap that aligns more closely with their projects. “Since this was project No. 1,” he said, “it was a little bit of an experiment.”
In order to be successful with SpeedCore, Joseph said, each project will have to be evaluated to make sure the system is a good fit.
“Conceptually, I can see where it would make good sense on projects that have very complex wall arrangements,” he said, “particularly when wall arrangements change from story to story because a straightforward concrete core on a tall building can be done (fairly) efficiently using self-climbing gang forms and panelized rebar.”
What could be a challenge for some steel fabricators and erectors, he said, is matching up prefabricated plates in the field.
“It’s impressive at Rainier Square that they were able to solve that challenge,” Joseph said.
Contractors should have several more examples by which to determine if SpeedCore is right for them, as MKA is designing six projects in California that include the system — four in San Jose and two in Oakland.
However, an East Coast project, Klemencic said, would open up a wider market and demonstrate that SpeedCore is not just for earthquake-prone areas but is wind resistant as well and that the panels can be bolted together, not just welded like the crew in Seattle did for better field control for fit-up purposes.
Looking ahead, though, Kruth is optimistic that SpeedCore will find its place in construction. “We get questions about it all the time,” he said. “People in the industry really want to try this.”