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RE: Na Near-Source Question

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If you are that near the Alquist Priola requires the strcture  to be set
back by a distance of at least 50 feet from the traces of the active fault. 

Also the soil engineer should have some exploratory trenches
in order  to detect the traces of the active fault in and around the site of
the proposed building.

-----Original Message-----
From: Martin W. Johnson [mailto:MWJ(--nospam--at)]
Sent: Friday, June 23, 2000 8:38 AM
To: seaint(--nospam--at)
Subject: Na Near-Source Question


>I am designing a building in Palmdale right on the San Andreas Fault with
>Na=1.5. I am using simplified design base shear; building is a simple
>one-story CMU box (no irregularities) so I can use reduced Na=1.3
>(1630.2.3.2). So far so good.
>Now the question: Can I use Na=1.3 when designing out-of-plane CMU wall and
>wall anchorage to flexible diaphragm per formula 32-2 (1632.2) or do I have
>to go back to Na=1.5?
The language of the code says, "The value of Na used to determine Ca need
exceed 1.1 (etc.)".  That means that you can use a value of Ca based on this
value, wherever the term Ca is cited in the code.  That includes determining
force at wall anchors as well as base shear.

If this building is really sitting "right on" on the fault then is has a lot
more problems than a couple of decimal values in Na could correct.  Have you
checked if the Alquist Priola Act will permit its construction?

regards, Martin