Strength of 3 inch C channel???

[Matt69olds]

I’m getting an early start on a couple of my winter projects.

I loaned my 20 foot car trailer to a friend. When he returned it to my house, he forgot to unplug the 7 way trailer plug. So now I’m replacing a bunch of wiring. I DESPISE scotch lock wire connectors!!!

My other trailer question, I’m lengthening the ramps. The existing ramps were 5 feet long, made of a pair of 3 inch C channel on either side, positioned like this ] [ with2 inch angle in between, covered with 11 gauge diamond plate.

My issue: I need to be very careful how I park when loading/unloading the car. If the ground is isn’t level (the truck is lower than the trailer, or the ramps are siting in a low spot) the exhaust will drag on the deck. Even if the truck/ trailer are level, the exhaust is closer than I would prefer.

My solution? I made the ramps longer, which improves the approach angle considerably. I added 2 feet to each ramp (which required a few modifications under the trailer for the added length). I welded matching C channel a angle iron to duplicate the existing ramps. I welded 15 inches of C channel to the flat side of the C channel, bridging the connection between the old/new ramps. I then covered everything with matching diamond plate. I’m not an expert welder/fabricator, but I’m pleased with the results.


Once it was all done, I stood back to admire my handy work. Now my concern, will the ramps handle the load? The trailer is rated at 10k. The heaviest truck I have had on it has been a 9600 pound 1 ton dually 4x4 diesel Ram pulling truck. I doubt the ramps will have any trouble with my 3900 pound Olds, but once I stood back and look at it finished, I’m a little concerned if I should ever need to put something really heavy on it I googled C channel load capacity, but the calculations and formulas are a little confusing.

Opinions?

 

[TubeTruck]

Provided you bridged the seam after welding it, and your welds had enough penetration, I think you should be fine. Am I correct to remember that @Paladin is a welder/fabricator? He might be able to shed more light on this than I.

 

[bucket]

7ft is a fairly long ramp. I'd imagine that if you were to load up a 9600lb truck again, you may see the ramps flex a little bit. But I doubt it would actually bend them. Just don't hit them with speed and they should be fine.

 

[wanderinthru]

As @bucket said. Get you a couple wooden blocks that fit up under where you joined the old and new, you should be golden.

 

[Dmack]

The easy solution would be to keep several wood blocks handy and shim them under the middle of the ramps when loading heavier vehicles.

 

[wanderinthru]

The easy solution would be to keep several wood blocks handy and shim them under the middle of the ramps when loading heavier vehicles.

Can't believe I found someone that types slower than me!! Lol.

 

[Frankenchevy]

If you look at most heavy equipment ramps, they’re supported somehow mid span. Many of them are wedges, some have a steel kicker to the ground mid span.

Im sure you are already aware, but just in case—a 9600lb truck is a fair bit past the load carrying capacity of your 10k trailer.

 

[Matt69olds]

On the rare occasions I do need to move something that heavy I’ll do exactly that. I’m sure there is a way to calculate the safe load of the channel, but I probably don’t have all the figures needed to figure it out.

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Thanks!

 

[bucket]

If putting blocks under the ramps, blocks under the trailer are needed too. This is assuming that the ramps simply hook onto the trailer.

 

[75Monza]

What I did on a few non dovetail trailers I had was welded on 2" round mounts at front corners of the trailer so I could temp mount some crank landing gear and lift front of the trailer so nothing dragged in the back. When done, just pulled em back off and threw then in the chain box.

 

[Matt69olds]

The trailer does have a slight dovetail. The back of the trailer is made from 6 inch C channel, with slots cut out for the ramps to slide out. The bottom front of the ramp has a price of 1.5 angle iron welded with a lip hanging down to prevent the ramps from sliding out too far.

 

[Matt69olds]

A picture is worth a 1000 words, if it would help I’ll post some pics later.

 

[75Monza]

I also fill the holes in my ramps between the cross bars with walkway grating so it's more of a smooth surface and tire dropping in between rails doesn't happen anymore.

 

[Bextreme04]

On the rare occasions I do need to move something that heavy I’ll do exactly that. I’m sure there is a way to calculate the safe load of the channel, but I probably don’t have all the figures needed to figure it out.

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Thanks!

The calculation for load on the ramps is pretty straight-forward. You should try and remember that for the most part you would never have even half the total vehicle weight on the ramp at any one time. Usually the weakest point is the attachment point which is why the heavy weight ramps are triangular and have a support at least right under the hinge or attachment point for the trailer. That way when you have a very heavy load it pushes the back of the trailer down only until the ramp touches the ground.

The other thing is that mathematically your maximum bending moment will be at the mid-point of the ramp span. If you have an unsupported 5 foot long ramp, your maximum bending moment would be at the 2.5ft point and would be roughly 2200lbs... so roughly 5500lb-ft at that point. Its not really correct, but just quick back of the napkin type numbers for you to see the relationship.

If you have a center support, you have now made the bending moment arm half of that length..... so 1.25ft. Which drops your bending moment in half as well to 2750lb-ft... which is pretty significant when you look at how that applies to calculating the failure load based on tensile strength of the C-channel. It gets more complicated when you have to analyze a design that includes angle iron and C-channel and how they are welded together, but can be pretty easily analyzed using some basic and free CAD design software with basic FEM analysis included.

You basically just create a CAD model of the ramps and then set a fixed load at any point. It will then show you how much tensile and compressive loads are at each point, which will show you any weak points or failure points based on the material you are using. I've used several different ones in school and also some ones for hobbies and 3-d printing. I personally like Autodesk Fusion 360 for ease of use, cost(free), and the huge feature set. You can even automatically convert your design to G-code and others to output to CAM, including a trial walk-through of the code to see any errors you might have.

 

[80BrownK10]

As @bucket said. Get you a couple wooden blocks that fit up under where you joined the old and new, you should be golden.

I was thinking the same thing. Block the ramps up if worried.