API-650 11th Ed - Seismic Cc Term

[richay]

API-650 11th Edition revised the equations for "Dynamic Liquid Hoop Forces". In equations E.6.1.4-4a and E.6.1.4-4b a new term (Cc) has been introduced.

Perhaps I'm being blind, but does anybody know where this term (Cc) is defined?

Thanks.

Richard Ay
COADE, Inc.

 

[notnowiambusy]

It's not defined anywhere that I could find and neither is the S term.

In July of last year (2007), I emailed a technical inquiry to Gordon Robertson at API (see below). His only response was, "We had many errors in appendix e and are fixing them…here is the current version that is under revision. This should be corrected and released in October."

The current version he refered to was a commented version that seemed to be for assigning who was going to fix what and contained no real corrections for these formulas.

He also didn't say in which October we should expect the correction to be released - obviously it wasn't 2007!

... Emailed technical inquiry ...

From: Tim Mulligan [mailto:tmulligan@tampatank.com]
Sent: Thursday, July 19, 2007 9:02 AM
To: Gordon Robertson
Subject: Technical Inquiry regarding changes to API STD 650, Appendix E


Mr. Robertson,

This is a technical inquiry regarding API STD 650 – Welded Steel Tanks for Oil Storage, 11th edition, June 2007, Appendix E, Section E6.1.4 - Dynamic Liquid Hoop Forces.

The equations for in API STD 650, Appendix E, for Dynamic Liquid Hoop Forces (Equations E.6.1.4-1 thru E.6.4.1.4-4) have changed from Addendum 4 of the 10th Edition to the 11th Edition. In Equations E.6.1.4-1 thru E.6.1.4-3, the constant terms have increased by a factor of 2.5(±) for SI units and by a factor of 4.0(±) for U.S. Customary units. In Equation E.6.4.1.4-4, the terms CC and S are not defined. These same equations as found in AWWA D100-05 match the equations found in Addendum 4 of the 10th Edition.

Are Equations E.6.1.4-1 thru E.6.1.4-3 correct in the 11th Edition?

What are the definitions of CC and S, as found in Equation E.6.4.1.4-4 of the 11th Edition?

Regards,

Tim Mulligan

 

[gdubyuh]

As notnowiambusy pointed out, the equations in API-650, 10th Ed, Add. 4 agrees with AWWA D100-05. In the previous release of AWWA D100-96, equation 13-24 contains the terms C1 and S, where C1 is the natural period coefficient (defined by Eq. 13-5 and 13-6) and S is the Site Amplification Factor from Table 27 of D100-96.

With that said, I have the Cc and S terms marked out of the equation in my API-650 11th Ed book, based on the word (from a API committee member) that these two variables were inadvertently included in an early draft of App. E, and not removed as they should have been.

 

[jaydees]

It is my understanding from the API committee meetings that there are several errors in the 11th edition app. E. There is an addendum to the 11th edition originally scheduled to be released in October or November of 2007 but now scheduled to be released sometime in February 2008. I am waiting to see what they correct.

 

[JoeTank]

Don't plan on any schedule that API advises you of. They haven't met a single release date schedule in years. Sad indeed.

Joe Tank