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By John Biggs
June 25, 2018
In all big construction projects, time is money, and few projects drag along as painfully slow as high-rise buildings. A new method of construction shows great promise to improve safety, reduce job site congestion and dramatically slash build times, combining off-site construction, modular construction and advanced steel work.
Known as composite steel frame or steel core construction, the new method involves stacking pre-built modular cores, built in factories and shipped to the job site ready to install. This eliminates the need for steel workers to wait, floor-by-floor, for supporting concrete to cure. Once the workers connect the pieces of the steel and pour concrete within the core walls, they can move onto the next floor.
Drastically Cuts Construction Times & Costs
Seattle-based civil engineering firm Magnusson Klemencic Associates (MKA) first developed this tall sheer wall system, and is in the process of building a 58-story office and residential tower in Seattle’s bustling downtown area utilizing this steel core technology, which will cost millions less and take 40% less time to complete than traditional construction. Eschewing the use of rebar, the system instead uses steel plates joined by steel spacing ties, with the space between the plates filled with concrete.
The resulting structure, known as Rainier Square and slated for an early 2020 completion, will end up being the city’s second tallest building. According to the American Institute of Steel Construction, Ron Klemencic, who led the development of the steel core system and recently received the distinguished engineering alumni award from Purdue University for his work, gave a presentation comparing the speed of a traditional concrete core versus a steel-concrete composite core. The concrete core building took 474 days to complete, while the hybrid composite core building took just 377 days.
“The 97 working day difference equals 136 calendar days, which means the owner will benefit from four-and-a-half months lower contractor’s overhead and general conditions costs, four-and-a-half months lower financing costs, and four-and-a-half months of earlier rental income,” Klemencic said.
Conventional methods including rebar-reinforced concrete is a painstakingly slow process, with each floor’s steel framing fully dependent on the progress of the concrete work. The hybrid method includes the strength and stiffness of a traditional reinforced concrete core structure without the drawbacks of jungles of rebar and intricate formwork construction. No waiting for concrete to set means the steel modules can continue to be stacked as it cures.
“It fundamentally changes the game,” said Klemencic.
Jon Magnusson, senior principal at MKA, echoed Klemencic’s view on the groundbreaking nature of the new method.
“This system represents the greatest innovation in steel in high-rise buildings in decades. It offers the performance of a concrete core with the speed and benefits of steel construction,” he said.
The Rainier Square project is only the first application of MKA’s technology at this scale, but Seattle isn’t the only state making use of stackable steel module construction.
Five projects so far in Colorado have been completed using Vulcraft’s CorTek Core System in collaboration with Vulcraft’s parent company Nucor. The CorTek system comes together using off-site built modular stackable steel cores, including stairs and railings, which provide easier access to subsequent floors as concrete poured into the cores below cure.
Easy as 1, 2, 3
According to Building Design + Construction, once the cores are delivered to the construction site, installing consists of just three steps: stack the cores, connect the steel, then continue erecting the structure, pouring concrete inside the walls of the core.
The CorTek system has been used for several projects around Colorado including the One Steamboat Place resort in Steamboat Springs, the Taxi II mixed-use residential building in Denver and the Limelight Lodge in Aspen.
Steel core construction represents a big leap forward for how the frames of buildings come together, and make use of several new construction technologies. It’s another strong use case for both offsite and modular construction. Reducing wait times and cutting through the human traffic jams of steel workers and masons clamoring for position within buildings under construction make the process easier and will result in drastically quicker and safer projects.
composite steel frame
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