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RE: Equipment Anchorage

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Larry,
You are supposed to design for the Fp value, but the amplification for 
vibration isolation is 2.0 as indicated in Table 13.6-1 footnote b which 
states: "Components mounted on vibration isolators shall have a bumper 
restraint or snubber in each horizontal direction. The design force shall 
be taken as 2Fp if the nominal clearance (air gap) between the equipment 
support frame and restraint is greater than 0.25 in. If the nominal 
clearance specified on the construction documents is not greater than 0.25 
in., the design force is permitted to be taken as Fp."

The exception applies if the air gap is small.  The intent is to limit the 
impact load as the vibration isolators reach their limit under seismic 
loads.  Granted, the commentary is lacking.  Your ap is 2.5 per Table 
13.6-1, but you have to multiply the Fp by 2 unless you have an air gap of 
0.25 in or less.

Impact loads in actual studies have been observed to be greater, but this 
was a consensus agreement for a bounding value.

There are additional requirements contained in section 13.6.5.5.4.

Regards,
Harold Sprague
> Date: Tue, 26 Nov 2013 14:40:53 -0800
> From: d.topete73(--nospam--at)gmail.com
> Subject: Re: [SEAINT-SEAOSC] Equipment Anchorage
> To: seaint-seaosc(--nospam--at)mail-list.com
> 
> Are you looking for footnote a to Table 13.5-1 of ASCE 7-05?  I do recall
> what you are referring to, but I can't locate it at the moment.  I think 
> I saw it recently in some seminar notes.
> 
> On Tue, Nov 26, 2013 at 2:15 PM, <lrhauer(--nospam--at)earthlink.net> wrote:
> 
>> I am designing the support of some roof top mounted mechanical 
>> equipment, (on an existing roof), that is supported by vibration 
>> isolators and, therefore, I have to amplify the seismic horizontal 
>> forces by 2.5, (Table 13.6-1 of the ASCE 7-05). These amplified forces 
>> would be used for the equipment anchorage to the platform and the 
>> platform to the roof framing. But, I somehow remember that in checking 
>> the existing roof framing the Ap can be reduced down to 1.0 from 2.5- it 
>> is only the connections that need to have the Ap of 2.5 used. But, I 
>> can’t seem to find this exception anywhere in the ASCE, (or ’10 

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