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Re: Component Amplification factor a.p

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The a-sub-p factor in the 1997 UBC represents the dynamic amplification
factor, relating the dynamic properties of the component to that of the
structure. Knowing the fundamental period of both the component and the
structure, this value can be exactly determined using basic dynamic

However,  since  this  value  is not practical, a-sub-p has been assigned a
value  based  on  whether  the  component  is either "rigid" or "Flexible",
a-sub-p  of  1.0  and  2,5 respectively.  This is analogous to the 1994 UBC
method of multiplying C-sub-p times 2 for flexible items.

If  your  equipment  is rigid, and not on vibration isolators (see footnote
14), a-sub-p of 1.0 is appropriate.  If not, a-sub-p of 2.5 is appropriate.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA


Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA


                    "Timothy P.                                                                                    
                    Spengler"            To:     <seaint(--nospam--at)>                                               
          >            cc:                                                                       
                    07/11/02 10:30                                                                                 
                    AM                   Subject:     Component Amplification factor a.p                           
                    Please respond                                                                                 
                    to seaint                                                                                ..... 

I'm designing  what could best be classified as a "structural" suspended
ceiling grid.   It's similar to a standard suspended ceiling, except much
stronger.  The  system will be hung from a roof superstructure using 3/4"
diameter threaded rods  and laterally braced with pre-stretched wire rope.
The ceiling grid itself consists of 4" deep x 2" wide  aluminum extrustion
tubes laid out on a 2' x 4' grid pattern and  will support, on average, 10
psf of self weight plus 12 psf of additional load  suspended for the
ceiling.  The ends of the aluminum extrusions will be  fully welded.

On the advise of another engineer, my client is dictating  that a component
amplification  factor of 2.5 be used for the seismic design of this system.
Upon  researching this item in the UBC and the California blue book I was
able to  technically determine that my system had a fundamental period
greater than 0.06  and could therefore be classified as a flexible
component and require an  amplification factor of 2.5.  However, there are
numerous items in Table  16-0 of the UBC that closely match my system (such
as suspended ceilings,  conduits and piping.) yet only require an
amplification factor of 1.0.   In addition, the  blue book seems to
indicate that the potential for seismic amplification  is reduced if a
system is ductile, therefore resulting in a  amplication factor of 1.0.
However, this is only mentioned once and I  would not consider it amble
evidence to refute using an amplification factor of  2.5.

My question to the  group is 1) Is there a more technically refined way
that I could prove that my  system can be designed using an amplification
factor of 1.0? and 2) Does anybody  know of any additional sources that
have a more detailed discussion of parts and  portions seismic analysis?


Tim Spengler  SE
Portland,  Oregon.

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