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RE: R-Factors Coldform hat sections

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The hat sections are trapezoidal in profile and are fixed by the lips or
lower flanges (rim of hat) being screw fixed to the face of the portal
frame.

I agree about the L-T buckling sensitivity.  In essence they perform similar
to a C profile bending about its weaker axis, so don't particularly
experience a lateral instability problem.

I have analysed the section using the CFS package of RSG Software (Bob
Glauz) which indicates one of the buckling modes involves both webs and lips
of the section buckling sideways when placed in compression subject to an
outward wind load. This I believe is the flexural-torsional buckling mode
that occurs at long wavelengths, 1 or 2 metres.  However this mode involves
rotation of the top of the hat.  

But similar to the C/Z profiles I believe torsional restraint is provided by
the decking or sheeting attached to the top flange.

To get a solution from the software a suitable R-factor would be necessary.
Currently the default is zero and the capacity for the member is very low.

I believe the R-factor would be between 0.7 and 0.9 but have no eveidence
(other than my gut!).

How does this strike you??


Roy Harrison
 
Roy Harrison & Associates
Consulting Structural Engineers
Adelaide - South Australia
 
mailto:ro35984(--nospam--at)bigpond.net.au
http://users.senet.com.au/~tectonic/

	-----Original Message-----
	

 


-----Original Message-----
From: Paul Ransom [mailto:ad026(--nospam--at)hwcn.org] 
Sent: Friday, 31 March 2006 12:56 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: R-Factors Coldform hat sections


> From: "Roy Harrison" <ro35984(--nospam--at)bigpond.net.au>

> Does anyone have R-factor values for coldformed hat-section purlins 
> using a flange-to-flange type connection.
>  
> We only have C/Z sections published using a welded cleat connection.

> Roy Harrison & Associates
> Consulting Structural Engineers
> Adelaide  -  South Australia

I'm not clear on your description or the reference to welded cleat.

North American Cold Formed Standard? R for bending with one flange
restrained? The values in the table were developed by test. Your hat section
probably does not suffer from the same L-T buckling sensitivity as a C/Z
with one flange restrained by attached panel so this simplified, reduction
approach may be irrelevent.

-- 
R. Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ado26(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

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