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RE: tube steel braces

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Title: RE: tube steel braces

From AISC Seismic Provisions Table I-9-1, b/t (or h/t) should be limited to 100/sqrt(Fy) for rectangular HSS. This does include square cross sections, since they are rectangles too. The 190/sqrt(Fy) limitation is for designs that need only meet the requirements in the basic specification (Specification for Struictural Steel Buildings), not those in the Seismic Provisions. In more plain language, this means that you need a smaller b/t ratio when you expect that the braces will withstand inelastic deformations to dissipate earthquake energy.

If you don't already have the AISC Seismic Provisions, you can get them here:

Make sure you also get Supplement No. 1 too here:


-----Original Message-----
From: david adie [mailto:dadie(--nospam--at)]
Sent: Friday, September 22, 2000 8:12 AM
To: seaint(--nospam--at)
Subject: tube steel braces

per 1997 ubc section 2213.8.2.5

from asd table b5.1, the max b/t ratio for square or rectangular tube steel
is 190 / sqrt(Fy)

from ubc section 2213.8.2.5, the max b/t ratio for rectangular tube steel is
110 / sqrt(Fy)

if i am using square tube steel, does the ubc requirement govern?  i have
heard engineers argue that it does because "square" is a subset of