API650 annular plate theory

[vesselguy]

Is there someone here who knows the theory or the basis behind API650's thickness sizing of annular plate? I know that it assumed the annular plate width calculation is based on the simplified assumption that the plate is a beam rigidly fixed and uniformly loaded with the distributed water load. However, I don't know why the thickness from table 5-1 is based on the stress in the bottom shell course. Anyone know why?

 

[JStephen]

I haven't looked at it in detail. But you could assume the bottom of the shell was pinned (or with yield moment in the bottom) and calculate the radial force applied to the annular ring from the shell. I think Roark's Formulas for Stress and Strain would allow this.

Whether the resulting load will lead to a derivation of the API formulas is a different matter.

 

[chicopee]

vesselguy-rigidly fixed how?

 

[carthago]

I believe it is an old publication (which used to be listed in appendix E of old revisions of API 650), title of this publication is =
Basis of seismic design provisions for welded steel oil storage tanks
Authors= Wozniak and Mitchell

This uses the theory of beam on elastic foundation

This document is retrievable for the net for free

 

[JStephen]

The annular plate requirements in Table 5-1 are unrelated to seismic provisions.

For the seismic loading, it really doesn't matter if the thicker plate is an annular ring or not; you're just lifting it on the outer edge and it acts in bending.

The Table 5-1 annular requirement is applicable to those tanks that are going to induce the most radial force into the bottom plate. Note the requirement of 5.5.3 requiring an elastic analysis in the case of certain tanks.

 

[JoeTank]

The annular plate requirements are based upon the amount of uplift of the bottom due to shell rotation. The uplifted length is calculated and the bending stresses are determined. The bending stress is limited due to assumptions about cyclic behaviour and shakedown. All these calculations have been performed and the requirements for thickness summarized in table in API-650.

Joe Tank

 

[vesselguy]

Reply to Chicopee:
From the book Structural Analysis and Design of Process Equipment by Jawad and Farr, some of the formulation of the formulas shown in API-650 are shown in the book. In it, it illustrated the annular plate width is calculated based on the simplified asumption that the plate to bottom shell joint is a rigid connection. Hence, it is modeled as a beam with a 0 degree of freedom on one end.

JoeTank,
the table you refer to must be table 5-1. If so, this is exactly what I am asking about. I just want to see the formulation that was done to make table 5-1 so I can understand what has been accounted for and how. Is there a book or paper that show this? I know, I should just shut up and follow the code. But I just want to know the details of the "black box", that's all.

Thanks all for responding.

 

[JoeTank]

vesselguy,
Guido Karcher wrote several papers in the late 1970s about the development of Appendix M. In them he had a good development discussion about rotations of the shell-to-bottom joint and how the annular plate was affected. Get those papers and you will see where the stuff in Table 5-1 comes comes from.

Joe Tank