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In response to your particular question, the answer is no.

You really have me confused. If you are looking at the D 100-96, the "force reduction factor" is Rw (not Rf) which is really a response factor and is independent of the ground shaking / seismicity.

It sounds like you are trying to fine tune a tank design. If so the "out of the can" D 100-96 is not the proper tool. Besides, it is the Z that defines seismicity (recurrence periods) and the ground shaking. All that aside, the rest of the seismic code world left much of the D 100-96 behind several years ago without MAJOR tweaking.

To get what I think you want, use the ASCE 7-02, Section If you want to modify the seismic probabilities, do it within the SDS and SD1 calculations. Don't modify the R. You will probably want a site specific response spectra developed for the probability that you desire.

I would also suggest that you read the FEMA 450-1 and FEMA 450-2, Chapter 14 for the commentary that led to the development of the tank provisions contained in ASCE 7-02. You will find similar changes in the ACI 350.3.

BTW, the D 100 is in the process of a major upgrade. I believe that it is being balloted now. Seismic is one of the MAJOR overhaul areas.

Harold Sprague

From: "Al Grathwol" <AGrathwol(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: "SEAOC List (E-mail)" <seaint(--nospam--at)>
Subject: AWWA D100
Date: Tue, 21 Dec 2004 12:00:35 -0800

According to AWWA D100, the force reduction factor Rf = 2.5 for a 10,00 year recurrence period. Is there a methodology for adjusting Rf for smaller recurrence periods?

Albert H. Grathwol
Phone (949) 476-3562
Fax (603) 971-0200

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