This is better than what I had up to now which is zilch.
Gary
Conrad Harrison wrote:
> Gary,
>
> 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
> achieve.
>
> 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.
>
>
> Regards
> Conrad Harrison
> B.Tech (mfg & mech), MIIE, gradTIEAust
> mailto:sch.tectonic@bigpond.com
> Adelaide
> South Australia
>
>
>
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