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Re: UBC Table 16-O, Penthouse Force Factors

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Anchorage forces for the penthouse should be designed in accordance with
1997 UBC Section 1632.  These forces should not be applied as loads on your
freezer structure.  The freezer structure should be designed in accordance
with 1997 UBC Section 1630.  The penthouse should be treated as weight/mass
at the freezer roof level.

In the event the penthouse mass is more than 25% of the total freezer plus
penthouse mass, I would recommend a combined model that considers the mass
and stiffness of the freezer and penthouses, designed in accordance with
1997 Section 1631.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

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                    Tim Close                                                                                      
                    <tim.close@mead      To:     seaint(--nospam--at)seaint.org                                                 
                    hunt.com>                                                                                      
                    04/13/01 10:13       cc:                                                                       
                    AM                                                                                             
                    Please respond       Subject:     UBC Table 16-O, Penthouse Force Factors                      
                    to seaint                                                                                      
                                                                                                                 . 
                                                                                                                   




I have a single story freezer building located in seismic zone 3 (14,000
s.f.). I have two small penthouses (30'x30' each) which house the cooling
units.
The penthouses are supported by H-frames in the plane of the freezer roof.

The lateral load resisting system for the penthouses are concentrically
braced frames with seisic forces considering the pethouses as elements per
UBC 1632 and Table 16-O.

The lateral load resisting system for the freezer is a concentrically
braced frame with seismic forces per UBC 1630.2.

The question is: After designing the bracing system for the penthouses per
the element requirements, can the seismic loads applied to the freezer roof
from the penthouse be scaled down so that the magnitude of these forces are
based upon the seismic coefficient used for the freezer?

Thanks for the help.




Timothy J. Close, P.E., S.E.
Mead & Hunt, Inc.
6501 Watts Road, Suite 101
Madison, WI 53719
Ph:  (608) 273-6380
Fax: (608) 273-6391
<tim.close(--nospam--at)meadhunt.com>

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