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Re: Factors

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These parameters are from the basis of seismic design in the US - ASCE7-10 
(Minimum Design Loads for Buildings and Other Structures).

Ss is a mapped, short period, spectral response acceleration parameter 
<> (essentially, 
 a location-specific seismic acceleration) - an important component for the 
 determination of the seismic force.  Ss=2.6 is very high, higher than for 
most of California.  Most of the equipment we design for is usually rated 
for Ss<=2.2.  This is not to say Ss cannot be higher - it can, in some areas 
 of California and, particularly, in the New Madrid Seismic Zone.

Ip is the importance factor for the calculation of the seismic force on 
non-structural components (ASCE7-10 Chapter 13).  Ip=1.5 for hazardous (health 
 or physical) or essential (hospital) installations, and 1.0 for other cases. 
 The force computed based on Ss and several other factors is scaled up by 
Ip to get the design seismic force.



V. Steve Gordin PhD
Licensed Structural Engineer

> On Feb 20, 2015, at 8:51 AM, Thor Tandy <vicpeng(--nospam--at)> wrote:
> I am reviewing a (US-supplied) roof top unit curb.
> The supplier has given two factors I am not familiar with.
> Ip (importance) = 1.5 and Ss (source) = 2.6
> Importance I understand but in Canada, "1.5" represents "post-disaster"
> The source factor I do not know . with regard to review of non-structural
> elements what is Ss and what do these two factors tell me?
> Hoping to align with Canadian factors . apples with oranges J
> Thanks
> Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE, FEC
> Victoria, BC

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