Jon-Paul Cardin, P.E.
JPCardin@SCAFCO.com
Use of cold-formed steel members started in both the United States and England in 1850’s
Although, use of steel framing limited up to the 1930 due to lack of design standards
1939 American Iron and Steel Institute (AISI) sponsored a research project at Cornell University to develop specification for CFS
In 1946 the first Design Specification was published by AISI
The Specification has been updated and revised incrementally over the years
In 2001 the first NASPEC was published in coordination with Canada and Mexico
In the 1980’s every steel stud manufacturer had products with different dimensional profiles, steel thicknesses, and design specification catalog
Standard steel thickness was a Nominal thickness 0.0359” for 20 gauge with tolerance of +/- 0.0030” (0.0329” – 0.0389”)
The tolerance was put in place because the steel mills could not guarantee minimum thicknesses during this time
By the end of the 1980’s the mill equipment was improved and the tolerances became tighter
1990’s - Present
In the 1990’s manufacturers decided to standardize the steel framing industry by developing two manufacturing associations – one for the east coast and one for the west coast
In 1998, these two groups merge into the Steel Stud Manufacturing
Association (SSMA) and standardizing the rest of the USA.
Currently, the SSMA, Steel Framing Industry Alliance (SFIA) and
Certified Steel Stud Association (CSSA) are the three manufacturers associations
Benefits of Designing with Steel
Consistent material quality
Noncombustible
Dimensionally stable
No Rot
No Freeze/Thaw Effects
No Warp due to Moisture
Insect resistant
Flexibility in design
Lightweight
High strength-to-weight ratio
Most recycled material
Member Section Properties
Allowable Span Tables
Interior Wall Heights
Composite
Non-Composite
Curtain Wall Heights
Combined Axial and Lateral
Floor Joist Spans
Ceiling Spans
Connection Capacity Tables
Composite Wall Heights
• Obtained from Testing at an accredited
Laboratory. Tests are performed with drywall attached both sides full height.
Non-Composite Wall Heights
• Calculated assuming drywall attached both sides fully braced condition. The code does not allow us to take the strength of the drywall into account.
Composite Wall Heights
Member
362S125-30
Spacing
12”
16”
24”
Non-Composite Wall Heights
Member
362S125-30
Spacing
12”
16”
24”
Deflection L/120 Deflection L/240
22’ 10” 18’ 3”
20’ 8”
18’ 1”
16’ 7”
14’ 6”
Deflection L/120 Deflection L/240
19’ 11” 16’ 7”
17’ 3”
14’ 1”
15’ 0”
13’ 2”
CFS 8.0 - RGS Software
AISIWIN - Devco Software
LGBeamer – Devco Software
Other Proprietary Software
North American Specification – NASPEC (S100)
Main Specification
Members, Assemblies, Systems, Connections
General Provisions (S200)
Floor and Roof System Design (S210)
Wall Stud Design (S211)
Header Design (S212)
Lateral Design (S213)
Truss Design (S214)
Prescriptive Method for One and Two Family
Dwellings (S230)
CFS Design Manual (D-100)
Section Property Calculation Examples
Member Design Examples
CFS Design Guide (D-110)
Full System Design Examples
Most failure modes of structural steel apply
In addition, CFS deals with thin/slender elements
Web Crippling
Local Buckling
Distortional Buckling
Flexural-Torsional Buckling
Utilize effective section properties
Web and Flange to Thickness Ratio Limitations for AISI Code
Equations
Flexural Members require bracing to resist torsion due to non-symmetric profile
Sheathing Both Sides
CRC Clipped to Stud
Flat Strap and Blocking
Sheathing One Flange with Rigid Bracing on Opposite
Flange
Sheathing is not adequate for axial bracing
Bracing to resist both torsion and lateral displacement
Brace forces accumulate along stud wall at 2% of axial load, so the forces must be terminated to the structure or floor system
Brace forces must be terminated to the structure or floor system
Flat strap cross bracing (Figure 5)
Stud orientated in plane of the wall (Figure 6)
Web stiffeners may be required at bearing locations due to web crippling
Web stiffeners required for h/t ratio between 200 and 260
h = flat portion of web
Ratio tables available in catalogs
Catalogs and software specify when required due to loading
Back to back member typically adequate web stiffener
Clips at member ends (head of wall or base connections) or bypass locations considered web stiffeners
In 2005, Dietrich puts UltraSteel on the market with the following characteristics:
Excessive knurling of the entire stud (dimpled)
Added a V-grove in the flanges
Increased steel yield strength from 33 ksi to 40 ksi
UltraSteel ended up NOT being a success, but it did open the door for the concept of engineered studs
The three characteristics that affect the strength of the stud:
Thickness
Profile
Grade/strength of steel
Why is it called EQ?
EQ is an abbreviation for “equivalent”
The strength of steel studs used to be related to the thickness of the steel, but with the engineered studs, that is no longer the case
EQ means that the stud is manufactured with thinner material, but produces equivalent strength as the mentioned traditional stud
Example: 33EQS vs. 33mil
362SFS162-33EQS 362S162-33
Design thickness
Steel yield strength
Allowable moment
0.0295
57 ksi
6.34 in-kips
0.0346
33 ksi
5.29 in-kips
Engineered Header and Jamb Systems
One and two piece pre-engineered systems available
Jamb is typically wide flange section
Clips connections from header to jamb studs
Consistent Installation and Connections
Consistent Installation and Connections
Member and Connection Capacities
Member section properties available
Typically proprietary software available
Published allowable loads for clip connection
Published Capacities Based on Testing
Test Ultimate Load and Serviceability Load (1/8”)
Reduction factor based on material tested
Safety factor based on test data reliability
Publish lower of serviceability and reduced ultimate load
Cold-Formed Steel Engineers Institute
www.cfsei.org
American Iron and Steel Institute (AISI)
www.steel.org
Wei-Wen Yu Center for Cold-Formed Steel Structures
www.ccfss.org
Jon-Paul Cardin, P.E.
JPCardin@SCAFCO.com