[How do I?] Reduce Flexing Of Ramp

dave_r_1

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I made some folding ramps for loading equipment on and off my flatbed, and they work ok, but they bounce/flex significantly (couple inch's) with me on them, and each section (1/2 of each ramp) has curved about 1/4" in the middle of the section from being flat after just a couple months of regular use. When I start loading/unloading winter equipment which is heavier, it'll just get worse.

The ramps are primarily made of 1.25" square tubing, 1/8" thick mild steel.
Each section is 52" long.

Here's a top view of a "section":
IMG_0580.jpg

And a side view of the extended ramp:
IMG_0581.jpg

I have considered having some kind of support in the middle, but given that the area around the truck when loading/unloading isn't always flat and/or even, it would get complicated to have some setup that would brace it right reasonably quickly.

I've got another set of ramps that my dad made, about 7.5 feet long, non-folding, also 1.25" square tubing, 1/8" thick, but I don't know what kind of steel (my dad made them and has since died), but with a couple of more cross members, and they don't noticeably flex for me. I would use them, but they are too short for using with the deck of my truck.

Would putting a diagonal or additional cross members help with the flexing, or do I have to remake the ramps with better steel?
 
I made some folding ramps for loading equipment on and off my flatbed, and they work ok, but they bounce/flex significantly (couple inch's) with me on them, and each section (1/2 of each ramp) has curved about 1/4" in the middle of the section from being flat after just a couple months of regular use. When I start loading/unloading winter equipment which is heavier, it'll just get worse.

The ramps are primarily made of 1.25" square tubing, 1/8" thick mild steel.
Each section is 52" long.

Here's a top view of a "section":
View attachment 132517

And a side view of the extended ramp:
View attachment 132518

I have considered having some kind of support in the middle, but given that the area around the truck when loading/unloading isn't always flat and/or even, it would get complicated to have some setup that would brace it right reasonably quickly.

I've got another set of ramps that my dad made, about 7.5 feet long, non-folding, also 1.25" square tubing, 1/8" thick, but I don't know what kind of steel (my dad made them and has since died), but with a couple of more cross members, and they don't noticeably flex for me. I would use them, but they are too short for using with the deck of my truck.

Would putting a diagonal or additional cross members help with the flexing, or do I have to remake the ramps with better steel?
Cross-bracing won't help. Your beams need more depth. I suggest doubling up each tube (the added tube need not be full length). That will require relocating your hinge, which will give you more strength there as well.
 
I'd make something like an adjustable jackstand that could be put in place where the hinge on your ramp is.
 
With the ground being of significantly varying height and potentially being uneven, as well as raising/lowering the ramps up to 30 times a day, jackstands would be annoying to unstrap, position and adjust twice each time (one for each ramp).

But the doubling-up idea sounds like it would work. Actually, it reminded me of something I did to strengthen another beam, and that was to weld angle iron to it. It'll stiffen up the whole length, but not take up nearly as much volume. And I could reduce/eliminate the existing bend using my press.

Thinking about it, just welding a strip of flatiron to each side of the section would help with reducing/eliminating the flexing...but I think I'll go with using angle iron.

Thanks for the help.
 
Today's phrase is "lateral torsional rigidity". On one ramp, I tried welding 4 additional cross members, and on the other ramp, I tried welding 1/8" angle iron to the outside of the ramp. The result was that both wound up about equally stiffened. Evidently my dad knew about this, where the more the square tubing is permitted to rotate, the more it will also bend. Adding the cross members greatly inhibit the tubing from being able to rotate, so it doesn't bend as much.

I made another ramp (to replace the one with the angle iron on it, as it's much heavier than the other one), and made the hinge area stronger by welding a length of 1/4" flatiron to the square tubing, then welding the 1/4" flatiron that I'm using as the hinge to that instead of just welding it to the 1/8" tubing.

But, it's dark and raining out now, so I'll test how it is tomorrow for flexing vs the other ramp. And I'll throw up a pic of the revised ramp
 
If you want to keep weight to a minimum, attach a wire cable to each end of the ramp with a turnbuckle to pull the cable taught.
Tighten the cable until the ramp is arched upwards. That way the ramp will be in compression and the cable in tension, creating a bridge like structure.

A variation of this approach to keep the ramp flat would be to add a block under the hinge so the wire cable bends at the block. Tension in the cable would create upward pressure under the hinge.
 
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I'm a big fan of triangulation for stiffness, I'd have made the sides long triangles with the hinge on the lower corner, bolts (bloody big ones!) at the upper to adjust for straightness under load
Ramp triangulated.png
You can add some bracing to the sides, or box them in with sheet steel, to gain more stiffness

Dave H. (the other one)
 
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