API 650 - Downward reactions on foundations

[EmilianoS87]

Hello, I've been looking for some information on how to calculate the load distribution of roof plates in shell and columns.
Table 5.21 of API 650 standard uses two areas, Arss and Arsc, being the area of tank roof supported by shell or columns. And also uses Wrss and Wrsc being the weight of the tank roof supported by shell or columns.

I understand both areas and weights are related with each other but the standard doesn't clarify a method to calculate weight distribution.

Any of you have any experience doing that calculation?

Thanks.

 

[JStephen]

Generally, you'd figure the rafter spacing at the inner end times the rafter length gives you a rectangular area and half of that is figured on the shell.
Then spacing at the outer end minus spacing at the inner end gives you a wedge shape, assume it's a triangle, and 2/3 of that wedge goes to the shell.
If you're actually designing the structure, you can work out loads directly without actually working out those areas.

 

[HTURKAK]

Table 5.21 of API 650 standard is for Uplift Loads . ( Table 5.21a—Uplift Loads for (SI) units and Table 5.21b—Uplift Loads ( United States Customary units)


Table 5.22 is for Unfactored (Working Stress) Downward Reactions on Foundations..


The weight distribution depends on type of roof and supporting structure..

For some typical roofs;

- Self supporting roof ( cone, dome , umbrella ..) Wrss = total wt. of the roof and Wrsc =0

- Roof with one central pillar Arsc = (1/4 )Ar and Arss= (3/4) Ar

- If there are column rows ( probably cone roof with one or more column rows, the rafters supported on girders polygonal at plan and supported by columns etc) , the loads shall be studied for each specific case..

If this is a real question, you may post the roof details and get specfic answer.

 

[EmilianoS87]

Thanks both of you.
I believe I figured out the weight distribution with your inputs and fixed the calculation spreadsheet.