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Re: Flat Bottom Tank Anchorage

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Mr. Yang,

I would like to answer your question from the viewpoint of an engineering mechanics solution versus an engineering design solution.

If you strictly look at this problem from an engineering mechanics point of view, maximum shear in the tank wall at a horizontal plane just above the base occurs at the 90 deg and 270 deg locations (if 0 degrees indicates the direction of the applied load). Minimum shear occurs at 0 deg and 180 deg. You can see this in Roark's FORMULAS FOR STRESS AND STRAIN (5th ed.), Table 17, Case 19. Shear forces in the bolts would be calculated using tributary lengths of arc around the perimeter of the circular tank wall.

One engineering design approach is to assume redistribution of the lateral forces to all the bolts equally. Others may take into account the friction force between the tank base and the subgrade. There is nothing wrong with this approach.

My suggestion is to follow an established tank design code with regard to the anchorage design requirements and do not worry about calculating the exact forces in every anchor bolt.

Walter Sawruk
Senior Consultant
ABS Consulting
5 Birdsong Court
Shillington, PA

Email: ws(--nospam--at)
TEL 610-796-9080
FAX 610-796-9081

At 06:05 PM 17-10-01 -0700, you wrote:
I have question regarding the design the anchor bolts for a circular tank
with bottom fully supported on concrete pad.
When a lateral load is applied to the tank, assume no fiction between the
tank and the pad, the lateral load is resist by the shear capacity of the
anchor bolts.  The maximum shear force per anchor bolt is occured on the
bolt located 90 degres from the direction of applied load, and minium  shear
on anchor bolts occure on the bolts that are in line with the applied
lateral load.  Consider the situation where there are only 4 anchor bolts on
the ring of the tank base, will there be any shear force at all on the
anchor bolts located in line with the direction of the applied lateral
force?  Are all the lateral force resisted by the 2 anchor bolts located 90
degrees each side of the load direction?

Thanks in advance.

Yi Yang

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