The results of a new engineering feasibility study from the Steel Framing Industry Association (SFIA) suggests that the structural integrity of cold-formed steel (CFS) could make it a viable framing alternative in the construction of high-rise buildings. The new study commissioned by the SFIA grew out of the trend toward taller building that is transforming urban skylines that is driven by higher land costs and the gravitation of both young and older residents to urban centers.
“The strength, durability, and fire resistance of cold-formed steel has long made it the material of choice for framing mid-rise structures,” said Larry Williams, executive director, SFIA. “With some architects advocating the use of combustible wood in taller mid-rise and even high-rise structures, SFIA decided to undertake a science-based engineering analysis to test the height limits of cold-formed steel construction.
“What we discovered amazed even us,” Williams said. “While CFS has been the clear choice for framing buildings up to nine stories, our analysis showed that the structural integrity of cold-formed steel theoretically could enable architects and designers to create CFS-framed buildings as high as 40 stories or more. This far exceeds what has been the conventional wisdom.”
The advantages of cold-formed steel framing offer architects, builders, and specifiers with a range of features and benefits that all contribute to shorter construction times, lower material costs, safer structures, and faster revenue generation. Compared to wood, steel has the environmental advantage of being highly recycled and infinitely recyclable. Steel is tough and does not rot, split, or absorb moisture. And from an aesthetic or architectural viewpoint, steel structures can easily deliver creative design options and excellent value.
“From a broader perspective, this means that architects and builders could well have a safe, cost-effective, and alternative to other framing materials for taller structures — as well as greatly expanded opportunities for the CFS industry,” said Pat Ford, technical director, SFIA.
The feasibility analysis was conducted by Pat Ford, P.E., who is also principal of the engineering firm Matsen Ford Design, headquartered in Milwaukee, with guidance from the SFIA Technical Committee. The results of the study have been presented to industry leadership, including technical committees of the American Iron & Steel Institute. The project has been named Matsen Tower in honor of Ford’s late business partner, John Peter Matsen, who also was a leader in the industry’s technical community.
Matsen Tower is a type R3 apartment tower with 10-foot story heights and 25-foot, 6-inch center-to-center spacing for demising walls. Two stairwells are situated at either end of the building, with a four-elevator central core and a central corridor that is typical for this type of building.
The framing system and layout follows conventional load-bearing cold-formed steel construction. Studs and joists are restricted to the generic C-shaped studs with web depths of 6 inches and 12 inches found in the SFIA Technical Guide to Cold-Formed Steel Framing Products. Framing members spacing is limited to 24 inches, 16 inches, and 12 inches; when required, repetitive members use a maximum of two studs.
In addition to the cold-formed steel framing system, basic construction materials include:
- lightweight EPDM (a durable synthetic rubber roofing membrane) on metal deck roof;
- lightweight 1-1/2-inch gypsum concrete on structural 0.6 C deck floor;
- lightweight exterior wall finishes of architectural metal, EIFS, or finished exterior cement board panels; and
- aluminum-posted balconies for each unit.
Ford noted that because the design varies the framing member spacing from wider in the upper stories to tighter spacing closer to the ground, special detailing was required to ensure proper load distribution where these changes occur, primarily at the 30th story (spacing reduced from 24 inches to 16 inches) and at the 25th story (16 inches to 12 inches). In both locations, more robust tube elements are required (continuous HSS 6-inch by 3-inch by 1/4-inch and HSS 6-inch by 4-inch by 5/16-inch for these locations, respectively).
Ford also noted that the 40-story building height is not actually the theoretical maximum, but that this project demonstrates what is possible with cold-formed steel when conventional design and generic framing is used.
“Cold-formed steel not only meets the demands of today’s mid-rise buildings, but can also be an important part of re-shaping the skyline of cities in the future,” Ford said.
Information provided by the Steel Framing Industry Association (www.cfsteel.org).