Page 390 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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COLD-FORMED STEEL DESIGN

9.2 CHAPTER NINE

FIGURE 9.1 Typical cold-formed steel members.

The AISI NAS lists all of the sheet and strip materials included in Table 1.6 (Art. 1.4) as applica-
ble steels, as well as several of the plate steels included in Table 1.1 (A36, A242, A588, and A572).
A283 and A529 plate steels are also included, as well as A500 structural tubing (Table 1.7). Other
steels can be used for structural members if they meet ductility and other requirements. The basic
requirement is a ratio of tensile strength to yield stress not less than 1.08 and a total elongation of at
least 10% in 2 in. If these requirements cannot be met, alternative criteria related to local elongation
may be applicable. In addition, certain steels that do not meet the criteria, such as SS Grade 80
(under ASTM A653, A1008, A792, or A875), can be used for multiple-web configurations (roofing,
siding, decking, etc.), provided the yield stress is taken as 75% of the specified minimum (or 60 ksi
or 414 MPa, if less) and the tensile stress is taken as 75% of the specified minimum (or 62 ksi or
428 MPa if less). Some exceptions apply. Suitability can also be established by structural tests.

9.2 MANUFACTURING METHODS AND EFFECTS

As the name suggests, the cross section of a cold-formed member is achieved by a bending opera-
tion at room temperature, rather than the hot-rolling process used for the heavier structural steel
shapes. The dominant cold-forming process is known as roll-forming. In this process, a coil of steel
is fed through a series of rolls, each of which bends the sheet progressively until the final shape is
reached at the last roll stand. The number of roll stands may vary from 6 to 20, depending on the
complexity of the shape. Because the steel is fed in coil form, with successive coils weld-spliced as
needed, the process can achieve speeds up to about 300 ft/min and is well suited for quantity pro-
duction. Small quantities may be produced on a press-brake, particularly if the shape is simple, such
as an angle or channel cross section. In its simplest form, a press brake consists of a male die which
presses the steel sheet into a matching female die.
In general, the cold-forming operation is beneficial in that it increases the yield stress of the
material in the region of the bend. The flat material between bends may also show an increase due
to squeezing or stretching during roll forming. This increase in strength is attributable to cold

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