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Compression flange bracing

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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 roof
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 UBC
permits the use of "approved national standards" (e.g. AWWA) for the design
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 lateral
support? I can't imagine AWWA recommending this design approach without some
sort of basis.