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RE: Cold Formed Steel

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Not aware of any tolerances for cold-formed steel. Sections can be made to
any dimension and shape, and for a multitude of applications, including
deliberately having curved flanges. So required tolerances would be
dependent on the application, some manufacturers do indicate what they can

There is some guidance for acceptable tolerances for steel house framing,
which is mainly channel like sections. The NASH draft specification, says:

D1.1.1 Cold-formed sections
a) Material thickness shall conform to AS1397.
b) Tolerances of sections, assuming design thickness, shall be determined
such that the relevant actual sectional properties are not more than ±5%
from the design section properties.
c) Tolerances appropriate for particular sections shall be specified to
comply with the above.

AS1397 is just a standard for the production of steel coil and strip,
probably derived from an equivalent ASTM specification.

One manufacturer of channel like sections indicates ±2 mm on depth and ±2 mm
on flange width. Assuming envelope method, then any actual shape which fits
between the envelopes for the maximum material condition (MMC) and the least
material condition (LMC) would be acceptable. Which suggests a maximum rise
or fall for curvature of about 1mm. Much less than the 5/16" (7.9mm).

Another guide is simply to use tolerances given in codes for hot rolled
sections. These tolerances should be based on requirements for suitability
for inclusion in finished construction, rather than based on expectations
from manufacturing process.

If the sections are meant to be flat and square then doesn't sound good,
both roll forming and folding should achieve better than described.

Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
South Australia 

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