[Shop-talk] Engineering question

[Brian Kennedy]

I looked at a photo online. Straps are about 1/4 of the length from the end which is where I would think you'd put them to minimize the bending. Hard to believe that your static stresses would be anywhere near close to what the tanks would see on an 18 wheeler pounding down the road.
Brian in MI




On Nov 27, 2016, at 4:45 PM, John Innis <jdinnis at gmail.com> wrote:

> 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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