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RE: Wall thickness of HSS sections
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- Subject: RE: Wall thickness of HSS sections
- From: "Mike Valley" <mtv(--nospam--at)skilling.com>
- Date: Fri, 23 Jun 2000 13:18:32 -0700
Code answer: The width-to-thickness ratio for HSS should be taken as flat width to wall thickness (AISC Seismic, Section 13.2). Therefore, even if 0.93xthickness is used, HSS10x10x5/8 still satisfies this criterion (for Fy=46 ksi). Rational answer: Dependence on sqrt(Fy) is based on mathematical formulation and, perhaps, general trends (not an extensive series of tests for the same section with different actual yield strengths). The limiting width-to-thickness ratio is based on pretty sparse data [one of the test programs reports b/t = 14, 25, and 30 which for the material tested were about 120, 197, and 228/sqrt(Fy)] and there is not a sharp transition in the observed behavior (assuming you could see that transition with three data points). The section b/t reported in the research is often based on the nominal thickness (not actual, measured thickness). Based on the limitations of the research behind the prescriptive code limits, I feel comfortable basing the checks on the nominal properties and dimensions. In other words, for the purposes of prescriptive section qualification, I don't get excited if the actual Fy is a little high (which, by calculation, would imply a lower b/t limit) or if the actual thickness is a little low (therefore, by calculation, b/t is a little high). Instead, I am more irritated by the reduction of overall section properties forced on us by unethical, unprofessional, legalistic, cheap, low-life steel producers; I am personally and professionally disgusted by the level of chiseling encountered in our system. I believe that the correct solution is to fix the material specs so that we get what we pay for, instead of moving to a system of "nominal" dimensions. Of course, what is right doesn't usually happen. -Mike Valley -----Original Message----- From: Alexander Sasha Itsekson [mailto:sitsekson(--nospam--at)ida-se.com] Sent: Friday, June 23, 2000 11:01 AM To: List server Subject: Wall thickness of HSS sections Hello, For some time now we were aware of the fact that the mills were rolling out tube sections on the lower end of the wall thickness tolerances. The AISC black book (hollow structural steel sections) indicates the actual thick nesses for the TS sections. It appears that the actual thickness is 93% of the nominal thickness for tubes. No, here's my question: how many engineers revised their braced frame design aids to account for the local buckling requirements that limits the wall thickness to width*sqrt(Fy)/110. Are you aware that we can't use the old good HSS10x10 in the braced frames at all (it requires the minimum wall thickness of .66")? Any comments? Regards, Alexander Sasha Itsekson INGRAHAM DEJESSE ASSOCIATES INC. (510) 527-7223 ext. 209
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