I am not an engineer, but I thought maybe this could be a very old and classic problem in structural/mechanical engineering. I need to build a support structure to hold a uniformly-distributed load of 75 kg (which has the shape of a square box). I can only use pipe and welding (or bolts+nuts). The only force it needs to hold is the weight of the box, there are not lateral forces expected (it will be placed indoors on a hard, level surface and will not be pulled/pushed from any of the 4 sides).

I wonder if there is a relatively well known and simple answer to these 1) what is the strongest structure possible? 2) what is the optimum case in terms of strongest structure possible using a minimum amount of pipe?

I drew a few options (front and side views) but I guess there could be many more and a large amount of combinations. Is this a well-known case? or maybe it doesn't matter much given the relation between the strength of the steel pipe and the "small" load?

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The distance between the floor and the bottom of the box is 70 cm. The box is 65x65x22 cm thus the pipe structure view from above is a 65x65 cm square (or that's how I would initially imagine anyway).

  • $\begingroup$ How high above the ground should the box be? $\endgroup$ Apr 19 '20 at 14:58
  • $\begingroup$ Thanks, it is 70 cm. I added that to the description. $\endgroup$
    – terauser
    Apr 19 '20 at 15:39
  • $\begingroup$ Do you mean 20mm box section? If 20cm it’s almost as thick as your load... $\endgroup$ Apr 19 '20 at 15:44
  • $\begingroup$ Is there a limit on the footprint also being 65x65 cm or could the base be larger than the load? $\endgroup$ Apr 19 '20 at 15:45
  • $\begingroup$ J. R. Swift, the pipe section is a square of 20x20 mm. The thickness of the wall of the pipe is 1.6 mm. The footprint has to be no larger than the box, thus yes it is limited to 65x65 cm $\endgroup$
    – terauser
    Apr 19 '20 at 15:58

Your load is too small to create high stresses.

But as a rule of thumb, your version 2 is the most unstable du to leaving one or more corners wobbly.

The first version is the most reasonable and it seems it has the optimal economy in the material used.

If your load was significantly more, then you'd think about locating your 45-degree braces in such a way as to reduce the free extension of the legs against buckling and at the same time watching for the length of the brace itself not to buckle itself.

The third version could redeem its excessive use of material only if the loads are sensitive to vibration and require stabilized steady support.


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