steel vs aluminum

[10secBu]

Been thinking about the possibility of building a second set of ramps for the car trailer I built a while ago. The current ramps are 12" wide and 60" long. There made of steel box tube which is 2" square and either .083" or .090" wall tube (forget which I used) ...tops covered in .125" steel diamond plate.

I wouldn't mind building a second set out of aluminum tubing with aluminum diamond plate. My question is...what wall thickness would I have to use of 2" square tube in aluminum to get the same strength as .083 or .090 wall steel tubing? What thickness aluminum diamond plate sheet would be needed for strength as well.

The ramps would need to be strong enough to support a pair of wheels with about 4000 lbs max for the pair, or 2000 lbs each ramp. The external size would remain the same being 12" wide x 60" long, 2" square tube frame.

thanks for any input.

[RHutch]

It would depend on the aluminum alloy used and the design of the ramp.
In my experience I would think 6061 Alloy 2x2x 3/16 or ¼ inch wall thickness with a shallow inverted truss design using 5356 filler metal and 100% penetration welds. One thing to remember when welding aluminum in a structural joint is to use a 60 degree included angle for all beveled weld joints. Also don’t use a super hot spray arc since it will reduce the temper in the material and boil off some of the alloying elements in the filler metal.

[10secBu]

It would depend on the aluminum alloy used and the design of the ramp.
In my experience I would think 6061 Alloy 2x2x 3/16 or ¼ inch wall thickness with a shallow inverted truss design using 5356 filler metal and 100% penetration welds. One thing to remember when welding aluminum in a structural joint is to use a 60 degree included angle for all beveled weld joints. Also don’t use a super hot spray arc since it will reduce the temper in the material and boil off some of the alloying elements in the filler metal.

The ramps have to be dead flat. They slide into storage holes which are 12 1/2" wide and 2 1/2" high.

What do you mean about the spray arc? I would be Tig welding the ramps together.

[RHutch]

When I referred to spray arc I was referring to the Mig process.
I generally think in terms of quick high quality production where a shop has to turn jobs quickly in order to turn a profit.

[dyn88]

2000 pounds per ramp is difficult to achieve but it is possible. You say the slot is 2.5" high, is this able to open up at all? if so you can build your frame and skin it both sides with diamond plate. Run 2 lengths 60" with one in the middle 56". The connect the three every 10"oc across. Finally skin the top with .186 diamond plate and the bottom with .125 sheet. the sheet on the bottom should prevent any kinking that may occur due to impact loading. Use .250 wall 6061 tubing and makesure it is clean,clean,clean. Lastly groove all your welds and for added insurance you can have the ramps stress relived at your local heat treater, just to insure that there will be no cracks occuring. I built a cat walk similer to this for a local helicopter manufacturer and the load rating was "1800 pounds safe load" per the engineer.

[Paul Seaman]

T6061 would be my first choice in 1/4" thickness. I would run 3 ribs the length and do shorter stringers in the width for the added strength and longavity. The plating preferance I would choose 3/16" or 1/4". The extra rib would add the extra strength to make the load possible. Two will just make the rating your looking for by a 20% margin, by the metal supply book but I overbuild everything so I never feel the pain of an embarrassing failure. Generally speaking if one of my assemblies fails, abuse was involved.

A car being loaded can have shifting weight variables well above the static weight of the vehicle so, overbuild it and be safe.

Peace,

[Teeps]

by a 20% margin, by the metal supply book
Peace,

So where does a Gent go about finding one of these Metal supply books?


Thanks in advance,

Don

[Paul Seaman]

Don:
My book is as old as the hills, with no cover, but check out the downloadable poster I found. http://www.saf.com/poster.html.

I can't tell how much is on it. My book has about 10 pages and came from a metal merchant. It gives WT per unit, Length per unit, strength per ft, deflection by WT/length. I'll check with my metal supplier next week see if they have a similar item and how much. Mine cost I think $3 about 10 years ago.

Peace,

[10secBu]

big correction needed

Cripes did I screw up. The ramps need to support 2000 lbs for the pair, not 2000 lbs each. They need to support 1000 lbs each.

How does this new info change the aluminum 2" tube wall thickness/diamond plate sheet thickness requirements???

The whole idea, if done, would be to reduce the weight of the ramps substantially. I really need to pull a steel ramp out and weigh it...believe there approx 60 or so lbs each right now.

The ramp opening cannot be opened up at all. Gotta work with the external dimensions.

I'm just not real familiar with the strength differences between steel and aluminum to know how thick of aluminum material is needed for comparable strength to the steel ones I have now.

[dyn88]

well half the load translates into half the matirial or a redesign. you could do without the third center member and go with .186 wall thickness and .125 on the top with .062 on the bottom. that gives you a thickness of 2" and3/16. Heres a hint to prevent the ramps from sticking in the holes- use candle wax to lubricate the friction areas. Also dont forget to make sure the aluminum is cCLEAN before you weld it.

[Sberry]

This is just a thought as this type of question pops up often. What does making them comparable to the strength of steel have to do with it? Did you engineer the steel ones? If I already had steel that was working I would likely leave well enough alone, but, if I was to make alum ones it would likely be 3 runs of 10 ga tubing under a 10 ga plate. All the welding is going to distort this thing anyway without some compensation by pre-cambering or maybe you could likely frame the tubings with some cross stiffners first then basically tack the plate on?

[10secBu]

This is just a thought as this type of question pops up often. What does making them comparable to the strength of steel have to do with it? Did you engineer the steel ones? If I already had steel that was working I would likely leave well enough alone, but, if I was to make alum ones it would likely be 3 runs of 10 ga tubing under a 10 ga plate. All the welding is going to distort this thing anyway without some compensation by pre-cambering or maybe you could likely frame the tubings with some cross stiffners first then basically tack the plate on?

The whole idea of the aluminum ramps is to save weight. I do have to pick these things up and move them every time I load and unload a car. I did design and build the steel ones and they work fine, just heavy. No signs of bending or bowing from use. I did have to use a torch to flame straighten the steel ramps to remove the bow they aquired from stitching on the diamond plate. I even put a 1/8" to 1/4" box in the opposite direction in an effort to keep them flat from use.

[Paul Seaman]

The 1/4" tubing is still right but go to 2 runners and 3/16" plate for the tread and you'll be golden. You'll still need ribs in between the rails, to keep it all straight.

Peace,