The thought of constructing a tower core without rebar would cause many builders to scoff.

But the project team behind a 58-story tower under construction in Seattle is working to prove that there may be a better, faster way to build tall.

Seattle-based engineering firm Magnusson Klemencic Associates (MKA) has pioneered a new type of high-rise building core that utilizes a concrete-filled composite plate shear wall system called SpeedCore. The system was used for the first time on Rainier Square, an 850-foot-tall mixed-use tower being built by general contractor Lease Crutcher Lewis.

The building was designed by NBBJ for Seattle-based developer Wright Runstad & Company.

Because the concept was utilized for the first time on such a high-profile project, there are a lot of eyes on the work being done.

“I would say the goal of Rainier Square was to score the touchdown,” said Brian Morgen, a principal with MKA. “Given the infancy of it and the newness of it, the city (of Seattle) assigned a very robust peer panel to review everything we were doing.”

The SpeedCore concept was actually borrowed from methodology used around the world to construct nuclear power stations, Morgen said.

“The loading is entirely different with blast and projectile,” he said. “You have thick walls for out-of-plane loading, while for tall buildings we’re using the same concept in a completely different manner. Extrapolating it to Rainier Square was the first real world application when it comes to high rises.”

So how does it work?

Because concrete in a building core is normally poured days or even weeks before structural steel is erected on the same level, the leading core method leads to completion of the building core long before the rest of the building catches up.

By contrast, erection of a SpeedCore structure begins with prefabricated panels consisting of two structural steel plates held in place with cross-connecting tie rods. After erection, the panels are filled with concrete, which is poured from the bottom of the panel. The resulting sandwich provides strength and stability along with significant on-site time savings.

It does away with the need for curing time entirely by eliminating the need for a leading core. Also, it eliminates the need for formwork, installation of rebar, embedded plates, sleeves and block-outs.

“In SpeedCore you could do two floors in one week,” Morgen said. “Now, what you’re doing is trading prefab time offsite to achieve that; that does have lead time associated with it.”

And now the involved firms know the concept works as intended.

The Rainier Square project topped out after just 10 months, achieving a construction rate of roughly 1.35 floors per week. The system has shorted the timeline of the project, which is slated for completion in March 2020, from 40 months to 31 months.

MKA is currently designing five new California high-rise buildings using SpeedCore concepts, including the 19-story 200 Park Avenue tower project in San Jose.

In order to realize time savings using the system, builders need to plan ahead. The pre-construction phase of a SpeedCore project is lengthened by the need for precision in drawings sent to the fabricator, as well as the time needed to ensure accurate fabrication of the steel panels. In addition, the long lead time allows for less flexibility later.

“With a concrete core there is more flexibility for MEP penetrations coming through the core later on,” said Shannon Testa, Rainier Square project manager for Lease Crutcher Lewis. “You can start steel and MEP coordination and MEP can even lag, because other than moving rebar around for the most part there aren’t any fly zones.”

With these steel panels, however, coordination of systems and trades must occur much earlier in the schedule.

Once that is done, however, the actual erection of the structure is far quicker than the traditional leading core method: up to 40 percent faster from start to topping out.

So far, the efficiencies gained through this process pencil out for a high-rise project like Rainier Square. According to MKA’s Morgen, the system is advantageous for buildings about 30 stories and higher. With further refinement, savings can be realized on smaller projects like 200 Park Avenue.

Lease Crutcher Lewis marketing manager Jordan Gevers said the nine-month time savings at Rainier Square was key in allowing the project to pencil out.

“All the numbers changed from red to black. It’s not only the up-front costs, but it’s the speed to market too. You’re spending less in the first place but earning money more quickly.”

Testa noted this would also depend on the cost of materials, as well as the anticipated building time period.

“When we priced it out it was a premium to use the steel core over concrete if you were just looking at direct costs,” she said. “When you figure in the schedule savings this became a much more cost-effective project,” she said. “You don’t pay for cranes, hoists, personnel and staffing costs; so all of those things more than offset the actual direct costs. But you won’t see that savings as much in a shorter building even though you have schedule savings.”

She said it is likely that as this building methodology becomes more common associated steel fabrication costs will fall. The concept is non-proprietary, and many steel fabricators will be able to produce a similar type of panel. The steel panels used on Rainier Square were fabricated in Portland by Supreme Steel.

“For commercial fabrication this is big plate steel, more commonly used in shipbuilding than in buildings,” Testa said. “There was, for sure, a learning curve in making these panels.”

As it becomes more commonplace, Testa added, that learning curve will become less steep.

“I think MKA’s design will get refined over time,” she said. “We were the pilot project for the use of this system in a high-rise. It was peer reviewed, but in feeling good about it, it also meant there were redundancies and overly conservative assumptions in some aspects. People will get more comfortable with it.”

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