API 620 ANCHORAGE RATIO 1

[oolivares]

Hello there,
Is it possible to have as a result on calculating the anchorage ratio as a negative value, according API 650/620 J<054 but in my calculations I obtain -6.57... because of the parameter "-Wint", by the way my design pressure is 4.3 psig,

 

[JStephen]

You calculate the J factor to see if the tank is stable without anchor bolts for pressure+seismic.
However, a tank with 4.3 psi is nearly always going to be anchored due to pressure alone- see the first sentence in 5.11.2.1 in API-620, for example.
Looking at the J equation, it appears that in any case where J calculates negative, anchorage is already required due to pressure alone.

 

[oolivares]

Thanks, JStephen,
So, according your answer, a negative value of the anchorage ratio "J" is permitted?
The software Tank gave me those results, take a look to the attachment, please. According the message in the software, the Tank is stable (for seismic loading) and do not require anchorage but I have to mention that for Wind loadings the software indicates to anchor the tank.

 

[JStephen]

That shows wt is 280.63 and wint is 1979.9, so pressure uplift is already 700% of dead load, so there's no reason to calculate J in the first place.
The numbers plugged in may be right, just the program should detect that the step is not needed and omit it.

 

[oolivares]

Thanks, JStephen. It is clear to me, now.