Need a book?
Engineering books recommendations...
Return to index:
OCBF & SCBF warnings...
- To: seaint(--nospam--at)seaint.org
- Subject: OCBF & SCBF warnings...
- From: Benjamin Maxwell <enginerd666(--nospam--at)yahoo.com>
- Date: Thu, 29 Mar 2007 11:29:37 -0700 (PDT)
Has anyone on the List seen or discussed the Steel Concentrically Braced Frames Preliminary Recommendations
article published in the March 2007 SEAONC News by the Seismology and Structural Standards Committee?
Big stuff...I think the results have been in for a while, but the committee has only recently decided to move forward with their early recommendations (perhaps someone with a deeper inside knowledge would comment).
"Recent test results on braces used in steel concentrically braced frames (CBF) indicate that many commonly used sections and brace configurations do not meet seismic performance expectations. Specific parameters that [sic] were shown to affect the ductility of braces, notably the net-section, section type, width-thickness ratio of the cross section, and member slenderness".
"...recent experimental test results indicate that bracing members that comply with current width-thickness limits fractured at drifts of 2% to 3% at design level forces."
Square and rectangular HSS shapes exhibited low cycle, fatigue-induced fracture. Oops. Not good. It looks like the committee is going to study possible modifications of b/t ratios and slenderness requirements, but also recommends using shapes less susceptible to local buckling such as round HSS and wide flange shapes. Apparently grout-filled tubes performed better as well.
- Reinforce the net section zone at the ends of the brace (another fracture-susceptible area)
- Use braces with low width-thickness ratios and moderate slenderness (too stubby and too slender can lead to poor behavior in their
- Use more stable cross sections (round HSS and wide flange, or grout-filled HSS round, square, or rectangular)
The following link is cited in the article, but I could not get it to work.
Maybe it's time to develop some wood moment connections?
-BenBenjamin H. Maxwell, S.E.
We won't tell. Get more on shows you hate to love
(and love to hate): Yahoo! TV's Guilty Pleasures list.