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En: Compression flange bracing

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-----Mensagem original-----
De: Ivan Lippi <ilippi(--nospam--at)>
Para: seaint(--nospam--at) <seaint(--nospam--at)>
Data: Sexta-feira, 29 de Outubro de 1999 18:49
Assunto: Re: Compression flange bracing

>API Storage Tanks
>Some years ago I was faced with the same problem. Purlins and the roof
>of a storage tank , designed exactly according to the API Code, erected in
>one day buckled immediately in the following day.
>A consulting engineer was hired to study the problem and produced quite a
>massive report but could not give a single credible reason why this was
>happening. He thought the cause was the roof plate  applying a lateral
>to the purlin!!!!
>The problem was given to me to solve. It was easy! In one page I
>demonstrated that the designer forgot to check the purlin deflection!
>Excessive purling deflection was causing the roof plate to detach from the
>purlin upper flange allowing it to buckle laterally.
>Without changing the purlin size, I recommended some stoppers be welded to
>the roof plate confining the purlin top flange lateral movement maintaining
>at the same time the rule prescribed by the API Code that the roof plate
>should not be welded to the purlin.
>Ivan Lippi
>Structural Engineer
>-----Mensagem original-----
>De: Fountain Conner <fconner(--nospam--at)>
>Para: seaint(--nospam--at) <seaint(--nospam--at)>
>Data: Sexta-feira, 29 de Outubro de 1999 15:51
>Assunto: Re: Compression flange bracing
>>>From over 30 years ago...  In design of power plants (non-seismic area),
>>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
>>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So far as I know, the law of gravity has not been repealed.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
>>> roof diaphragm. This is specifically permitted by AWWA D100, which
>>> 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.