Top and Intermediate Wind Girders API 650 1

[TheEverest]

Can anyone please help me with section 5.9.7.2? I could not understand what does "W" represent in the given equation. What is the meaning of Actual width of shell course?

 

[IFRs]

Presumably you are looking at 5.9.6.2, which mentions "Actual width of each shell course". In this context W means the vertical height of the shell plate. If your tank is 40 feet high and it is made of 4 equal height shell courses, this number is 10 feet. It is a little confusing I guess but in this context "width" is meant to be the short dimension of the shell plates. For instance, many shell plates are 8 feet x 32 feet, and described as width x length or 8 x 32. When installed, the "width" is placed vertically, becoming "height". Note that you are comparing the actual height to the transposed height. Both are vertial dimensions.

 

[TheEverest]

Thank you IFRs for your reply. Okay, I am clear about the width. But still I am in confusion regarding the section 5.9.7.2 (b). If I have 4 equal height shell courses of 10 feet width each, do I need to find transposed widths of each 4 courses putting the actual thickness (t actual) as their respective thickness; or find transposed widths for only those having the shell thickness same as that of top shell thickness?

 

[IFRs]

The general game plan is that it is too complicated to determine the resistance to wind buckling for a tank with varying thickness courses. So, we convert this multi-thickness shell assembly into one of uniform thickness. We imagine a new tank that is of one uniform thickness. Then the simple equations can be used. We could assume the entire height of the tank is only as thick as the thinnest course but that would be too conservative. Each course that is thicker than the thinnest would offer somewhat greater resistance to buckling. What we do is to say that a thicker course of some height (width) offers the same buckling resistance as a shorter course of a thinner thickness. These transformed heights (widths) are added together to give us a tank of uniform thickness that would have the same buckling resistance as the original tank of varying thicknesses. Then we proceed with the buckling analysis using this imaginary tank that is shorter but of a uniform thickness (that of the thinnest course).

It's kind of late here, does that make sny sense?

 

[TheEverest]

Yes, I am really grateful to you for your answers. I am doing a detailed study in API 650. I might ask more questions in coming days, hope to get reply. Thank you IFRs.

 

[TheEverest]

After calculating the minimum section modulus of the stiffening ring from 5.9.6.1, are we supposed to compare the value with that in table 5.20a and 5.20b to choose appropriate anlge for the stiffening ring?

 

[IFRs]

Yes