API 650 Wind Stiffeners 1

[Maxster]

I need to design a replacement wind stiffener/walkway on an existing 60m floating roof tank. The old walkway was typically as Detail 'e' of figure 3.20 in API 650 but was 1100mm (43") wide and 10mm thick. However, when I use the formula in 3.9.6.1. of API 650, the required section size (3600cm³) is outwith that given in table 3.20. My question is whether table 3.20 limits the width to 1000mm (40") with a required thickness of 6mm plate or whether I can replace like for like and still comply with the code.

 

[TankDude]

I believe that this could become a common trend for tanks located in coastal regions in light of the recent hurricane damage and subsequent changes to API 650 referencing ASCE 7. Anyway, to answer your question, I have always operated under the assumption that table 3-20 gives you some common sizes for reference. With high design wind pressures and large tanks you have no choice but to custom design the wind girder. If you are going to follow detail "e" then you will want to try to keep the thickness workable for the required bending during fabrication. The minimum width and vertical depth can be manipulated to match an ideal thickness (I recommend 3/8").

 

[JStephen]

On large wind girders, it may be convenient to go to heavier plate with narrower width than shown in the table. And some configurations are acceptable but not shown in the table- rolled channel, for example. And not every angle size is shown in that table, either.