tank anchorage

[Engr ZANIA]

hello,
Is there any criteria; based on dia to height ratio, to check anchorage requirement in vertical liquid storage steel tank ???(other than formulas mentioned in API650)

 

[JedClampett]

I don't think you can just use height to width, you need the wind and seismic loads, too. In California, you might need anchorage for a tank that you wouldn't in New York.
Note that the tank design guidelines really discourage anchorage of tanks. They tend to rip out during a seismic event and the contents leak all over the place.

 

[dik]

Jed: a 'passive' concrete curb, all around?

Dik

 

[MJCronin]

Jed,

Could you tell us the specific guidelines that you say discourage anchorage of tanks in seismic zones ?

MJCronin
Sr. Process Engineer

 

[racookpe1978]

Wind loadings are always critical, even if no seismic zone criteria.

 

[JStephen]

There are various criteria in API-650, AWWA D100, ASCE 7, etc. The wind loading, seismic loading, and anchorage criteria vary in each standard. In the last several editions and revisions of API-650, the wind overturning criteria has been revised each time, so for a new tank, you need to refer to the current edition. Both wind loading and seismic loading vary considerably depending on location, so there is no single criteria based on height/diameter ratio.

 

[JedClampett]

I've been to tank seminars where the instructor talked about anchorage being a problem during seismic events. I'll have to check my slides.

 

[TLHS]

Not anchoring lets the tank rock and dissipate energy. Your forces on the system are smaller in a rocking case, and you don't see the strong point loads at the anchor points. This is great for us.

Rocking, however, can be really bad for the mechanical system. If you look at the ASCE 7 recommendations, the seismic deflection capacity that you need to build into mechanical systems that tie into unanchored tanks is quite a bit larger than for unanchored tanks. So you need to discuss with other parties.

I default to unanchored gravel foundations whenever possible.