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RE: Table 16-q Seismic Coefficient Ca, Zone 4.

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The drop is because for soft soils, the high frequencies tend to be damped
out for high levels of excitation, such that for Ss equal to or greater than
1.0, short-period spectral accelerations tend to be smaller on soft soils
than on rock.

Harold Sprague

> -----Original Message-----
> From:	Jeffrey Flansburg - seaint [SMTP:seaint(--nospam--at)]
> Sent:	Friday, May 05, 2000 11:05 AM
> To:	seaint(--nospam--at)
> Subject:	Table 16-q Seismic Coefficient Ca, Zone 4.
> I have a question in regard to Table 16-Q ('97 UBC) for the seismic
> coefficient Ca.
> For Zone 4, in going from soil type Sd to Se, why does the coeff. drop
> from 0.44*Na to 0.36*Na?
> Jeffrey T. Flansburg, EIT
> John W. Parkin Engineering
> 500 Washington St.
> Vancouver, WA  98660
> (360) 694-8378 ext. 104
> (360) 694-3376 fax