[Shop-talk] Engineering question

[John Innis]

Yes, truly an engineering question.  It has been many years since I was in
engineering school.  But I know the answer to this one.  You have not
provided enough information to answer the question.  We would need to know
the wall thickness of the tank and type of aluminum.  Measuring the wall
thickness should be pretty easy, but figuring out the grad of aluminum may
be very difficult.  I suggest giving up on the engineering and resort to
shade-tree mechanics.  Use a piece of 3/4" plywood and cut a radius in it
to match the tank, then bolt this between the upper arms of the 4x4 to make
a cradle.  Stack enough pieces of plywood together to match the width of
the strap used on the truck.  You know that method was sufficient under the
dynamic load of a moving semi.  Should be more than adequate for a
stationary tank.  It also has the added benefit of tying the 4x4's together
at the point of load, so outward bending stresses will be reduced.  Your
4x4 x ' should be fine as long as you use through bolts of adequate size to
join the together in the middle and to bolt the ties at the base.  To help
insure the load on the 4x4's are minimized, you should cut the bottom ends
to match the angle, so the sit flat on the floor.

On Sun, Nov 27, 2016 at 2:48 PM, Matt <mbarre at juno.com> wrote:

> I hope you all had a great Thanksgiving and have plenty to be thankful for!
>
> I am adding diesel storage capacity to my shop.
> I got a good deal on an aluminum semitruck fuel tank ( 26" diameter  68"
> long) and need to construct a stand for it.
> These are normally secured on the truck with metal straps or bands.
>
> For my stand I am considering constructing large "X" from pressure treated
> 4x4 and resting the tank in the upper V.
> I would tie them together with 2x4 s to keep them from cocking.  I figure
> I would be safe with 3 Xs if any doubt, 4 to make sure.
>
> Question:  If I went with only 2 supports and kept them out on the ends,
> would the bending moment (bowing) threaten the integrity of the tank?
> 150 gallons is about 1000#.  Similarly, would the reduced "contact patch"
> of X mounts vice continuous straps threaten the tank walls?
>
> I am sure I could dig out my old *Statics* book and find the equation,
> but don't have a design bending limit for the tank.
> I am anticipating that just 2 supports, especially out at the ends would
> be too risky.
>
>
> Thanks for your thoughts,
> Matt in GA
>
>
>
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