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RE: Braced Frames - Hollow Strucural Sections

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Mark-

I haven't taken the time to find this provision in the 1997 UBC or the AISC
Seismic Provisions for Structural Steel Buildings, but, in the 1994 UBC,
section 2211.8.2.3, if you designed as tension or compression only (>70% of
the total force), you had to design for 3Rw/8 times the design force. This
is probably an Omega sub naught issue in the 1997 UBC, although I have not
found the specific code section.

Regards,

Bill Allen, S.E. (CA #2607)
ALLEN DESIGNS
Laguna Niguel, CA
http://www.AllenDesigns.com


||-----Original Message-----
||From: Mark D. Baker [mailto:shake4bake(--nospam--at)earthlink.net]
||Sent: Wednesday, May 10, 2000 10:22 AM
||To: seaint(--nospam--at)seaint.org
||Subject: Re: Braced Frames - Hollow Strucural Sections
||
||
||Why not just design the braces as tension members only and
||save yourself the
||headache you are now facing for compression member design?
||
||Mark
||
||
||----- Original Message -----
||From: Ron O. Hamburger <ROH(--nospam--at)eqe.com>
||To: <seaint(--nospam--at)seaint.org>
||Sent: Wednesday, May 10, 2000 8:26 AM
||Subject: Braced Frames - Hollow Strucural Sections
||
||
||>
||>
||> It is possible to use large HSS in braces of braced frames.  The
||requirement on
||> h/t is for "unstiffened" elements of sections.   This
||requirement was
||added in
||> 1994 to prevent braces from experiencing premature local
||buckling and "oil
||> canning."  When this happens, very large strains occur at
||the yield lines
||in the
||> local buckle and fracture initiates after a few cycles.
||>
||> It is possible (and laboratoy testing has demonstrated
||this) to fill the
||tube
||> with a noncompressible material, such as cement grout, and
||use lower h/t
||ratios.
||> The grout fill stiffens the tube so that the faces are no longer
||"unstiffened
||> elements."  This prevents the local buckling from occuring.
||>
||> Refer to the papers by Hassan and Goel, 1991 and Goel and
||Tang, 1989 upon
||which
||> this code provision is based.
||>
||>
||>
||>
||
||
||