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Re: Compression flange bracing

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>From over 30 years ago...  In design of power plants (non-seismic area), I
asked how we could consider bar grating as lateral support for the top
flange of grating-support members.  The answer was that the beams would not
be loaded if it weren't for the load on the grating.  If the beams are
loaded, we can count on a 20 percent coefficient of friction for lateral
support.  And 20 percent of the vertical load is gracious plenty for
lateral support.

So far as I know, the law of gravity has not been repealed.

Now, you "seismic dudes" may want to come up with some other restrictive
rules, but it remains that beams which aren't loaded don't buckle.  And if
they're loaded on the top flange, they *might* have a bit of lateral

Fountain E. Conner, P.E.
Gulf Breeze, Fl. 32561

> From: Lutz,James <JLUTZ(--nospam--at)>
> To: seaint(--nospam--at)
> Subject: Compression flange bracing
> Date: Friday, October 29, 1999 10:33 AM
> The issue of compression flange bracing has come up in my practice on
> numerous occasions with respect to rafters supporting the roofs of steel
> water storage tanks. Typical practice is to not weld the rafters to the
> plates, so compression flange bracing is only provided by friction of the
> roof diaphragm. This is specifically permitted by AWWA D100, which allows
> rafters to be designed as if continuously braced.
> The argument I get into when reviewing the work of other designers is
that I
> think UBC (AISC Specifications) should overrule the AWWA procedure. The
> permits the use of "approved national standards" (e.g. AWWA) for the
> of ground storage tanks (UBC 1634.4), but I read this as applicable to
> seismic design only. In all other aspects, the UBC should govern as is.
> Anybody have any thoughts on the validity of counting friction for
> support? I can't imagine AWWA recommending this design approach without
> sort of basis.