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Re: Class H

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Hey, Gary!

Rough day at the office? Maybe you got back some BRRAGG scores (I
completely forgot to go to write the exam. My secretary/wife gave me
heck for not teling her so she could write it in the schedule).

Thor's contact suggests that in seismic applications there are ductility
benefits as a result of reducing the strain-hardening effects. I suspect
that is a 2 sided sword:
1) when compression controls (e.g. global buckling), Class H (stress
relieved) will permit a lighter section with (presumably) greater
ductility in the stress relieved regions.
2) a lighter section has less material and therefore more deflection and
less energy absorbing capacity than a similar heavier section.

Square/rect HSS only benefit from significant residual stress relief in
the corner regions and, if seam welded, along the seam. Maybe 10% of the
section area in a 10x10.

Circular HSS, if cold-formed and seam welded, are evenly stressed around
the perimeter and not to the same extent as the corners of sq/rect HSS.
So the benefits will be different.

It is my understanding that most common size HSS produced in NA these
days is produced through a die, hot and has only nominal "cold-forming"
to ensure tolerances. I'm sure that is not the universal practice and
definitely not for extreme sizes.

I'm certain that there is a web-site to describe this more completely.
Also, I'm certain that somebody can point us toward
documentation/testing/research on materials from current production
techniques.

CISCs commentary to S16 is silent on the issue of Class C vs. H, even
for seismic. However, look at clause 27.5.3. The commentary discusses
the issue of post buckling fracture but ignores Class C vs. H.

I have this impression that there may be some corrosion resistance
benefits to using Class H but I would probably spec a corrosion
resisting steel before I would hang my hat on that.

All that said, I have never felt the need to spec Class H and it is
definitely not mandatory by S16-01.

Paul

> From: "Gary Hodgson & Associates" <ghodgson(--nospam--at)bellnet.ca>

> Re my previous reply. Not the people who replied to your e-mail. The
> people who always specify Class H are idiots.
> Gary
> 
> On 9 Jun 2005 at 19:56, dave lowen wrote:
> 
> > Thank you to all who responded. I believe I thought it was mandated
> > since every project that crosses my desk requires class H for
> > compression members.
> > 
> > It is certainly not readily available in my neck of the woods.

> > From: Paul Ransom [mailto:ad026(--nospam--at)hwcn.org] 

> > > From: "dave lowen" <jatech(--nospam--at)kwic.com>
> > 
> > > Can anyone point me to chapter and verse (in Canada) that states
> > > that HSS compression members must be class H?
> > 
> > There is no such requirement. Ummm... if you find one, let me know...


-- 
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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