Cold-formed steel (CFS) framing is a versatile building material because it can be connected to a variety of other materials. But how do you make those unions work? How do you connect CFS to hot-rolled steel, aluminum, concrete, masonry, or wood?
The answer has to do with the standard provisions for each material.
“You need to look at the design requirements as defined by the material that you’re connecting to,” said Roger A. LaBoube, Ph.D., P.E., Director of the Wei-Wen Yu Center for Cold-Formed Steel Structures at Missouri University of Science and Technology, Rolla, Missouri. “What you’re trying to achieve is optimal connection strength.”
Why integrate CFS framing with other materials
Designers fasten CFS framing to other materials for a variety of reasons. A designer may want a certain architectural appearance. The architect of Chart Industries’ renovated factory offices, for example, wanted a building with an aluminum exterior. He achieved his design intent by integrating CFS framing, rigid exterior foam insulation, a mineral fiber insulation rain screen, and aluminum metal panels.
In some cases, local codes mandate certain material combinations. A municipality may legislate that all new structures use brick or stone veneers, for example. The builder would use special ties to connect the CFS framing with the brick or stone.
Often, multi-material systems feature CFS framing for its deflection characteristics. To create an effective lateral force resisting system, concrete or masonry will be used at elevator shafts and stairwells. But, CFS stud shear walls can be added to share some lateral load.
Of course, economics can also drive the union of CFS with other materials. Architects and engineers may choose certain combinations of materials based on a project budget. For example, a structure could feature load-bearing CFS-framed walls connected to a wood-framed roof.
How to transfer loads between materials
The key to getting these connections between CFS and other materials right involves understanding the specifications for each material.
You’ll want to consult:
- Commentary on the North American Specification for the Design of Cold-Formed Steel Structural Members from the American Iron and Steel Institute (AISI S100-16, 2016 Edition).
- North American Standard for Cold-formed Steel Structural Framing (AISI S240-15, 2015 Edition)
- CFSEI Technical Notes — F Series on Fastener Hardware
- Standards for each respective integrating material — concrete, masonry, wood, etc.
Take AISI S240-15, Section B1.5.6, entitled “Connection to Other Materials,” for example. It states:
Bolts, nails, anchor bolts or other fasteners used to connect cold-formed steel framing to wood, masonry, concrete or other steel components shall be designed and installed in accordance with the applicable building code or the approved construction documents.
“We’re looking to the building code to guide us in the design of connecting CFS with other materials,” LaBoube said.
AISI S100-16, Section J7.1.1, entitled “Bearing,” equates material connection with load transfer. It states:
Provisions shall be made to transfer bearing forces from steel components covered by this Specification to adjacent structural components made of other materials.
The process of connecting CFS with other materials is “nothing unique or magical,” LaBoube said. “It’s a matter of recognizing that we need a load path. The load path has to transfer from the cold-formed steel, through the connector, and into the other material.”
This is where you’ll need the strength equations for the other material — the concrete specification, the masonry specification, the wood specification, etc. AISI S100-16, page 151, says:
When a cold-formed steel structural member is connected to other materials, such as hot-rolled steel, aluminum, concrete, masonry or wood, the connection strength should be the smallest of the strength of the fastener, the strength of the fastener attachment to the cold-formed steel structural member, or the strength of the fastener attachment to the other material.
According to LaBoube, interfacing CFS with another material requires “looking at the strength of the connection in the CFS as well as the connection strength required by the other material.”
This information will you started in transferring loads in multi-material systems, but if you have additional questions about making proper connections between CFS and other materials on your next CFS-framed project, request complimentary project assistance from our team of experts.