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Re: Roof Equipment

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1997 UBC, Section 1634, covers all "self-supporting structures other than
buildings".  Equipment supported by a building or structure above-grade is
not self-supporting.  1997 UBC Section 1632 covers "attachments for
permanent equipment supported by a structure" and is the correct section
for these items.

1997 UBC Table 16-O Item 3.C has an error that is covered by published
errata.  It should read " Any FLEXIBLE equipment ... ".  Flexible equipment
mounted on the roof should have a high design value.  If your equipment is
rigid, 1997 UBC Table 16-O Item 3.B may be applicable.  See 1997 UBC
Section 1627 for definitions of rigid and flexible components.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

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                    <lrhauer@earthl                                                                                
                    ink.net>             To:     SEAOC <seaint(--nospam--at)seaint.org>                                         
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                    nk.net                                                                                         
                    07/13/02 10:51       Subject:     Roof Equipment                                               
                    AM                                                                                             
                    Please respond                                                                           ..... 
                    to seaint                                                                                      
                                                                                                                   
                                                                                                                   




I'd like to get some opinions on what seismic forces others are using for
anchoring roof top mounted mechanical equipment, particularly with a Ca of
0.57 for Southern California.



Table 16-O is pretty explicite in Item 3,C that an Ap of 2.5 and Rp of 3.0
be
used, therefore Formula 32-2 seems to kick in, since these values are not
in
the "non-building" formulas. With Hx=Hr, Formula 32-2 results in a strength
Fp
of 1.9Wp and ASD force of 1.36Wp, which seem awfully high.



Any opinions?



Larry Hauer, S.E.

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