Steel Water Tank Supported On Matt On Piles

[TomWaggoner]

I have a steel water tank. Supported on a concrete matt on piles.

The seismic analysis of the tank using ASCE 7 and some other sloshing equations yield a base shear coefficient of Cs= 0.06 Wd. The tank and fluids weigh approximately 60,000,000 lbs. Believe it or not it has a 12 second period. Therefore, low base shear

So the shear at the base of the tank is about 3600 kips.

The matt of concrete weighs approximate 65,000,000 lbs.

So, to design the piles for seismic resistance, would you
1. Take the weight of the matt and multiply by 0.06 and add it to the tank base shear to get 3900 + 3600= 7500 kips?
2. Apply some other coefficient (R value) to the weight of the matt. Short period, huge value Cs=0.25Wd, and get 16,250 kips then add that to the 3600 kips for the tank. 3600 + 16250= 19,850 kips.

I lean toward solution 1, but I don’t have any literature to support it.

Any ideas?

 

[msquared48]

Looking at the matt footing, and considering the lateral forces using the top of the footing as a seismic base for the water tank, I would ask:

1. How much lateral soil pressure against the mat, including frictional forces at the base, to resist whatever lateral load is applied?

2. Where can the matt footing go considering the passive and frictional forces?

The frictional forces alone have to be equal to 20 to 30% of the total weight of the system. Seems likew this would be more than your seismic forces to be resisted, even at the higher level.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[TomWaggoner]

Passive yes. Friction No. Piles don’t allow friction forces to form.

 

[Once20036]

I've always thought of seismic base shear as occuring at the ground level, so whether or not to include a load for the pile cap depends on your geometry.

 

[TomWaggoner]

Ok,. thanks msquared48 and Structural20036 for pitching in

 

[msquared48]

Tom:

True. Duh!

Guess you have to use batter pile then unless the pile can take all of the lateral load via shear capacity.

If the site is in a soil liquefaction zone, you can't even use passive pressure come to think of it.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[TomWaggoner]

Ok thanks msquared48!

 

[abusementpark]

Steel Water Tank Supported On Matt

Poor fella.