API 650 11th Edition - Seismic Anchorage 1

[PEStructural]

Hello,

API 650, 11th Edition, Section E.6.2.1.2 has equations for seismic anchorage. However, Section 5.12 in combination with Table 5-21 has equations for seismic anchorage as well.

The question is, how have you approached the two conflicting equations? Do you look at both and use the most conservative number? Or...?

Also, when a tank is not required to have seismic anchorage (J <= 0.785), but anchorage is required for wind, do we need to look at the seismic uplift equation in Table 5-21? Or do we just look at the equations that are requiring anchorage (i.e. wind in this case)?

Please help!

Thanks!

 

[JStephen]

I have assumed that the newer equations were intended to take precedence over the old; that revisions were made but that other revisions required to match them were not made.

You can download a draft version of Rev. 1 from API's website and see if any of this is proposed for update.

Generally, the equations should give similar answers. The anchor uplift is just based on Mc/I - P/A cast into various forms.

If a tank requires anchors for wind or pressure, you should still size the anchors and chairs for seismic load, even if seismic load by itself would not require anchors.

 

[JoeTank]

Keep an eye out for the first addemum to API-650 (due out any day now they say?). It corrects a bunch of errors in Appendix E and adds a commentary(a new Appendix EC).

Joe Tank