/diy/ - Do It Yourself

>>1519053
>Charts don't go below 2"
Those are charts for structural members in buildings or other big structures. 1.5" isn't strong/stiff enough for that.

>the calculator seems suspicious
It doesn't explain its methodology very well, but I think I figured out what's going on.

>>1519055
>Calculator says for 500lbs:
>>60" span? 1-1/4 0.072 (15 ga)
>>30" span? 7/8 0.083 (14 ga)
>Seems like overkill.
It's actually underkill. That's the result without any deflection limit, meaning that it's using the plastic section modulus. That is, that's the size of tube that will barely hold the load without failing outright, and it will be permanently and seriously bent after a single load cycle. The deflection-limited column is fairly close to my estimate for a maximum stress of 36ksi (the yield stress of typical mild steel). It probably either has a modest safety factor or a larger safety factor relying on the somewhat greater strength of formed steel.

Some factors to consider though. That calculator is about a single beam carrying all the load. The replacement bracing will need multiple beams to reduce the unsupported span of the planks to an acceptable amount. 16" is a standard floor joist spacing distance.

Another thing: the stiffest part of a structure carries the greatest portion of the load, proportional to its stiffness in relation to other parts that could carry the load. Running any tubes along the 60" length won't do much. They would help distribute the load between the 30" tubes, but if they're the same kind of tube, it won't distribute very much because they would flex twice as much for a given load, and resting one end on the 30" span would add the 30" tube's flex to its own. The ones you have running along the 60" edges don't do much at all structurally, since the support boards are right there. Something like pic related would be a more efficient arrangement. The plank ends on the right don't need a tube under them since they rest directly on the support board.