CEMP-E
TI 809-07
NOVEMBER 1998
CHAPTER 2
COLD-FORMED STEEL DESIGN
1. INTRODUCTION. There are three design methods available to the designer: direct
application of the AISI Specification, prescriptive methods, and testing of designed assemblies.
The AISI specification can be used for the bulk of design calculations when selecting beams,
columns, web stiffeners, and effective section properties. AISI has guides for shear walls and
cold-formed steel trusses. These design guides can be used for Corps of Engineers projects, but
are limited to all steel designs. The use of plywood and oriented strand board are not allowed in
permanent Military design. When a designed assembly does not fall within the limits of these
design guides, those assemblies must be tested. The prescriptive method that follows should
only be used within its stated limits, and was created to serve the single family housing industry.
2. PRESCRIPTIVE METHODS.
a. General. One method of designing one and two family homes is to use the Prescriptive
Methods for residential Cold-Formed Steel Framing, by the U.S. Department of Housing and
Urban Development and the National Home Builders Association. The limitations for the
prescriptive method of design are summarized in the table below and apply to residential type
construction. Building loads are determined by using the ASCE 7-93 Minimum Load Assumption
for Buildings.
Table 2-1. Summary of Prescriptive Methods Limitations
Web depths
Deflection Limits
Bearing Walls
Heights
Walls
Remarks
100 mm (4")
2.4 to 3.0 m (8 to 10 ft)
L/240
Total Load
150mm (6")
2.4 to 3.0 m (8 to 10 ft)
L/360
Live Load
Joists/Rafters
Spans
Joists
300mm (12")
2.4 to 4.9m (8 to 16 ft)
L/240
Total Load
350mm (14")
2.1 to 6.4m (7 to 21 ft)
L/480
Live Load
400mm (16")
3.9 to 7.9m (13 to 26 ft) Rafters
Ceiling Joists
Spans
L/180
Total Load
100mm (4")
2.4 to 4.9m (8 to 16 ft)
L/240
Live Load
150mm (6")
2.7 to 7.0m (9 to 23 ft)
Ceiling Joists
200mm (8")
3.0 to 7.9m (10 to 26 ft)
L/240
Total Load
250mm (10")
3.7 to 8.2m (12 to 27 ft) Headers
300mm (12")
3.7 to 8.8m (12 to 29 ft)
L/240
Total Load
Flange 41 mm
Max House Width
L/360
Live Load
(1.625")
11 m (36 ft)
Lip 13 mm (0.5")
Notes:
1. Self-drilling and tapping screws: SAE J78, use a minimum edge and end distance of 3
diameters, a minimum of three exposed threads, and components in contact with each other, no
gaps between connected parts. In connections that are in shear only, a minimum edge distance
of 1.5 diameters in the direction of the force shall be used.
2. Dimensions in this table were originally in U.S. Customary units. Light gage steel materials
are available as soft metric equivalents.
b. Material Thickness. Designers need to specify the Design or Nominal thickness of the
material required. However, the minimum thickness of material that can be delivered to the job
site is 95% of the design thickness specified, see Table 1-1. When using this method of
specifying materials the designer will always get a material thicker than the minimum shown in
2-1
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