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# Steel HSS Compression Analysis

• To: <seaint(--nospam--at)seaint.org>
• Subject: Steel HSS Compression Analysis
• From: "David Maynard" <davemaynard(--nospam--at)ceincorp.com>
• Date: Wed, 17 Aug 2005 13:38:36 -0600

```Here's what I got.  I have a tube shape, 2" wide by 4" deep by 14 ga.
(0.0747" thick).  I'm using LRFD 3rd Ed. Nov. 10, 2000 HSS Design
Specification found within.  I check my Slenderness Limits as described in
Table 2.2-1.  Assuming, because this is not an AISC shape, that Fy = 33 ksi,
I found Lambda r to be 41.5.  My controlling wall slenderness ration, h/t,
lambda is 50.5, which exceeds the lambda r.

Flipping to section 4.2 of this design spec, I see that if lambda is greater
than lambda r, for rectangular HSS, Q = effective area/Ag.  It then states
that the effective area is equal to the summartion of the effective areas of
the sides using be = <long equation>.

The question that I run into is, what does this mean, "effective area"???

Do I have to use this equation for both wall dimensions, first with b and
then with h???  Or do I just use this equation as a substitute for b and
leave h untouched, even though that is the controlling slenderness limit???

And once this question is answered, I'm assuming I just take these adjusted
dimensions, multiply them by the thickness and combine all four side for an
effective area.

Right now, and I'm not sure if this is my illness/vacation talking but, this
just doesn't make any sense to me.  Can someone shed some light on the
situation???

Sincerely,
David Maynard, PE
Gillette, Wyoming
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