API 650 - When to use anchor bolts ?

[carthago]

API 650 tanks with earthquake and wind
I never understood correctly when to use anchor bolts or not ?
Of course I' d rather avoid them !

Which criteria are used to lnow of anchor bolt are required or not ?
Check if bolt tensioning is positive ?
Check if stress with sismic are high at annular plate ?
Check if there is a wind overturning ?

I am a bit confused...


Any straight procedure or specific litterature ??

thanks a lot

 

[IFRs]

You use them anytime there is a calculated uplift. Internal pressure, wind and seismic each or together can trigger anchors. API 650 is pretty clear on this, I think.

 

[JStephen]

Due to the way the standard is set up, you can calculate positive bolt tension even in cases where you don't need anchor bolts.

See 5.11.2, E.6.2.1.1.1, Fig. F-1, etc, in the 11th Edition.

 

[carthago]

Gentlmen,

Thank you for the tips.

 

[plantguyjj]

Will someone please explain how the anchor bolts are subjected a net uplift by internal pressure alone, with no wind or seismic? The first load case in Table 3-21 for uplift due to design pressure only seems to evaluate the shell separation from the floor, how would this case by itself trigger the need for anchorage?

thanks

 

[JStephen]

The bottom plate isn't rigid enough to resist loading acting as a flat plate. It depends on the soil underneath it to support it. What would actually happen if you overpressured an unanchored empty tank is that the shell would lift up several inches or more. The bottom plate near the shell would lift up with it, and would still be resting on the foundation back away from the shell.