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# pseudo-static coefficient

## pseudo-static coefficient

(OP)
Hi all,
According to WSDOT Getechincal Design Manual(6.5.3.1), horizontal pseudo-static coefficient Kh=0.5*PGA, the PGA at Everett, WA is 0.3, so I think Kh is 0.5*0.3=0.15.

But I read some getechnical reports, Kh=0.5*0.3*1.18=0.177 was used in these reports.  what does 1.18 mean?

Thanks

### RE: pseudo-static coefficient

wshi,

Suggest you contact the author of the reports containing the 1.18 factor...

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

### RE: pseudo-static coefficient

Probably it's the soil amplification factor, variable according to stratigraphic sequence:

the formula would go: Kh = Ag/g * S for foundations, and
Kh = 0.5 Ag/g * S for retaining walls, S stands for Soil (amplification).

I'm answering based upon european EC8 guidelines, but I saw in IBC and NEHRP the rationale is the same.

### RE: pseudo-static coefficient

wshi,

The 1.18 is the soil amplification factor.  It is used to take the peak bedrock acceleration (PBA) to peak ground acceleration (PGA) and is used to account for site soil amplification.  The PBA in Everett is 0.3.  The PGA is 0.354.

PS.  I am part of the I-5 Everett HOV project D/B team.

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