Flex/Steel Strength

[JayRS4]

Afternoon all. I`ve got some car ramps to make up, 12ft long, 18 inches wide, "rungs" every 5 inches.

They will be unsupported over the length, with one end 2 foot high, the other on the ground.

I`m thinking 50x30x3 RHS for the rails, 30x3 angle for the rungs. I dont have to use RHS for the rails, but it helps in the design.

So, my question is, will the rails be strong enough? Working on a maximum vehicle weight of 1800kg (estate). I`ve tried playing with Superbeam, but i`m obviously useless as I cant figure it out. It`s not quite as simple as sticking a load at the centrepoint.

Any help appreciated, I`ve been searching though the old ramp threads on here but most are angle rails anyway.

Ta muchly, Jay

Edit: Any sorry for the mix of metric and imperial, it`s just the way my brain works (when and if it works)

 

[oilcooled :)]

the strength of mildsteel is 208 giga newtons per metre squared, which is 208000000000 newtons per metre squared, divide by gravity 9.81 = kg metre squared= 21202854230 kg/m2. that means if i had a square block of mild steel 1 metre wide, 1 metre long and 1 metre deep i would have to apply 21202854230 kg to break it. this is probable not much help, but there is maths formulas
i can get them for you out of my mechanics notes later if you want. i think thats right

 

[Welderpaul]

The sizes you are thinking about using are not really big enough. I'd probably look at using something like 100x50x5 rhs for the rails and 50x5 angle - it will still deflect a bit, but i would have thought if you make it from 50x30x3 it may well fail.
Hardly portable though!

 

[Drains]

Jay, you can make the ramps out of dead skinny material, for lightness, but you need to get depth in there for strength. You could use 50 x 30, fine, (or smaller) but you need to back it up with sheet - 2 or 3 mil, back to more shs (25 x 25, say), to create an engineered joist-like structure - a bit like this...



Very strong and relatively light.

Doesn't need to be fully welded - stitching would be fine. You're looking to distribute the point load of the tyres over a much larger area. Think triangles.

 

[JayRS4]

Hmm, i might have to rethink this one. Just so we`re all talking about the same thing, the ones here http://duratray.net.au/index.php?link=aluminium-loading-ramps are pretty much what i`ve got in mind, only steel. The problem with using a bigger section for the rails is the approach clearance, and front overhang on cars.

Using my car as an example (although a bit of an exception to the rule) I have a 90cm overhang and 10cm clearance at the front. So a 1:9 gradiant. The ramps at 12 foot long and 2 high give a 1:6 gradiant. So by the time the wheels get to the ramp, the ramp height at the front of the bumper is 15cm, plus however much the rungs are sunk into the rails.

Actually, i think i`ve just over complicated things for myself using that example. Small stuff just confuses me, the last set of ramps I made had 120x60x5 rails, same for rungs and then 4.5mm treadplate.

Drains, are you suggesting a triangulated ladder frame for the rails? Damn I wish I understood solidworks or cad, would make life a lot easier with these things.

 

[outofthefire]

Why cant you have them supported? If you could that would make your life easier and safer.

 

[BChild]

Using my car as an example (although a bit of an exception to the rule) I have a 90cm overhang and 10cm clearance at the front. So a 1:9 gradiant. The ramps at 12 foot long and 2 high give a 1:6 gradiant. So by the time the wheels get to the ramp, the ramp height at the front of the bumper is 15cm, plus however much the rungs are sunk into the rails.

Then there is the problem with the length of the ramps at a shallow angle in order to get a decent height at the end of the ramps

I've got a set of ramp extenders and they are as long as the ramps themselves but solve the problem

I'll try and find a picture

Oh and the state of the drive is not down to me - a mate decided to park his car on it when he had a transmission coller leak!!!

 

[JayRS4]

Yup, i think a set of mini ramps to get on the ramps will be needed, or as we call it in our club, "nismo wood". Didn`t realise you were a Mitsubishi owner, i could of sworn you were one of the vw lot. I do like the FTO`s, impossibly pretty cars for there age (in a modern sense)