Anchors Shear load for vertical tank 1

[401laurent]

Hi,
I have to size Anchorage for vertical tank on 4 legs, for which only seismic loads govern ,after calculation per IBC code, the seismic moment is 145 kips ft, and the seismic shear is 8 kips.
As the BC anchors is 96 in, the tank height is 30 ft, and the total tank weight is 160 kips.
conclusion the tank do not require anchors. No tension loads on legs.
And the Shear loads of 8 kips Can be retined Only by friction of 160kips on concrete flor.

So my question . This conclusion is it right?
I am asking This question because some structural engineer said to me that per rule of the thimbs the anchors Shear is about 15 per 100 of the total tank weight
Do you khow This rule and is is correct for This case.
Thanks.
Laurent.

 

[msquared48]

Depends on a lot of factors but primarily the seismicity (Ss and S1) of the location of tank, and the R value of the lateral system used. If you are in a low seismic zone, you could be correct, but not in Washington or California.

My initial thought was that your seismic should be more in the order of 20 to 30 kips. But that would be factored by my comment above, and the fact that I am in Western Washington, a relatively high seismic zone.

I assume that the 160 Kip weight included the fluid weight too?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

And the sloshing effect if the material contained is a fluid?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[401laurent]

Hi msquared48,
Yes the 160 kips includ the fluid weight,effectively I m in low seismic east Canada (suppose Like zone 1 under UBC 97 code),
But you didnt talk me about the rule of 15per100,is it known rule, I nevers heard.
Tanks
Laurent

 

[msquared48]

Generally, not a "rule" per se, except when speaking from a specific location and type of building.

That engineer probably designs structures in the range of 13% to 16% seismioc values - mostly shear wall structures would be my guess.

The comment stems from his experience to which he has assigned a personal "rule of thumb", more precisely termed.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[401laurent]

Thanks msquared48,
If we suppose that the shear is 15/100 of 160 kips let say 24 kips, is it enought to require anchors for this tank. There is no tension loads on the legs.

Thanks.
Laurent.

 

[SAIL3]

I assume this is indoors as you did not mention the case of wind plus empty weight...
Personally I do not trust relying on friction for seismic resistance..despite all the fine tuning going on in seismic design, to me it is still an approximation, especially in the area of structure/grade intrerface where you can get a vertical seismic component...too much variability, depending on site conditions and location...so that rule of thumb is probably taking all of this into consideration...experienced engineers don't always spell out, at length, the logic of their engineering judgement....

 

[msquared48]

I would agree that except for the case of shear-friction, the use of fiction is not allowed in the IBC. I view the existance of the phenomenon as an addition to the safety factor for static conditions.

Throw in the mix of seismic forces that can occur both laterally and vertically, and I totally disregard any contribution to the resistance from frictional forces as they become totlly unreliable.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dhengr]

A second and a third.... I wouldn’t count on friction as a means of dealing with base shear.

 

[FiniteElemet]

I have a similiar problem, my question is if the tank drawings show vertical and horizontal earthquake loads, does it mean client is providing Q(e) and i have to multiply with rho to get E(h). Also, should I assume the listed vertical earthquake load to be E(v), such that listed value is actually {0.2*S(ds)*D}?