allowable uniform load for steel channel?

My buddy wants to build some ramps to load a skid steer onto the back
of a flatbed. He plans to build 2 ramps, each of which is built like a
ladder. The side rails will be steel channel and the cross pieces will
be steel angle, all hot rolled, welded. He has asked my help in figuring
how light he can build it. I figure his Bobcat weighs around 4000 pounds.
I own a Ryerson Steel data book which has allowable uniform loads for
steel channels but it doesn't go down to the 4" or 3" channel he's
considering. I can't find any useful specs online, not because I haven't
googled, but because I get way too much wrong information or because I
can't think of the smart way to limit or phrase the search string.
In particular, I want to know the allowable uniform load in ksi of 4" and
3" channel, each the lightest channel made (approximately 3/16") with a
span of eight feet.
Anyone?
Grant Erwin
Kirkland, Washington
Reply to
Grant Erwin
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Grant, The 8' is gonna kill you dimension wise, and crawling a skid steer that far in reverse is liable to kill someone else. Is there no way to dovetail the back end of the rig and get down to some conventional triangle shaped ramps?
(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net
Reply to
DanG
I bought a set of ramps for my Bobcat, which were used by the previous owner to load a Bobcat into a dump truck. I haven't tried them yet and I'm not sure how well they will really work or how scary the ride will be! I think they are 11' long. I can take some measurements next time I am in my yard.
Reply to
ATP*
According to my cheat book for 'C' section channels: Size Web Section Modulus 3"x6# .36" 1.38 3"x5# .26 1.24 3"x4.1# .17" 1.10 4"x7.25# .32 2.29 4"x5.4# .18 1.93 ---------------------------- 6"x8.2# .20 4.38 8"x11.5# .22" 8.14
Stength is proportional to section modulus so take whatever tables you have and work from there. Generally, 3" is 1/3rd as strong as 6" and 1/5th as strong as 8". 4" is half as strong as 6" and 1/4th as strong as 8" YMMV.
Cheers.
Grant Erw> My buddy wants to build some ramps to load a skid steer onto the back
Reply to
RoyJ
For what it is worth, when I worked at Boeing I asked an engineer there basically the same question. I was building ramps for my brothers trailer. I used 3" channel because he told me that it was sufficient for up to 6000 pounds. Hopefully this goes along with the information you're getting. Mine was spanning approx 6 feet.
Lane
Reply to
Lane
I've added another column for the Beam Resisting Moment for A36 steel to the table below. You need to specify the loading conditions and the beam's supports to calculate the actual bending moment in service. You also need to consider the beam's unsupported length to determine lateral stability.
Ned Simmons
Reply to
Ned Simmons
What do you mean by "The 8' is gonna kill you dimension wise"?
Do you mean if I build this I won't be able to lift it? Or it will be somehow difficult to build? Or I won't be able to buy steel that long? Or what?
GWE
DanG wrote:
Reply to
Grant Erwin
I take it to mean that 8' is a LONG span for 3" material. One way to look at things is to take the ratio of the length divided by the channel depth. In this case it would be 32:1 That is pretty skinny and flexible.
Grant Erw> What do you mean by "The 8' is gonna kill you dimension wise"?
Reply to
RoyJ
Thankyou Roy, that is what I meant. It will end up so heavy it will be a bear to load and/or be so flexible that it will be scary.
(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net
Reply to
DanG
The loading on this type of ramp is not uniform. It is a moving concentrated load. Whole different [design] ballgame. I have a pair made from 3" channel that were later beefed up with 4" welded over them. Takes two men and a large boy to move them. Bugs
Reply to
Bugs
Not really. You start out figuring the uniform load (or looking it up in a table), then you divide your max allowable load by 2 to translate it to the worst case (load concentrated midspan) then you add your fudge factor for dynamic loading (i.e. moving). The tables all list uniform load, that's why I asked for that spec. Your statement is completely correct, of course. - GWE
Reply to
Grant Erwin
Problem is that skid steers have really quirky loading factors when you are trying to go down a ramp in tight quarters. In this case, you would need to figure the full load on the downward axle, the majority of that load on one side when you correct a bit, a bit momentum hit when you try and stop coming down the ramp, and then some factor of safety.
As for weight, if you used 4" with 2"x 3/16"x12" crosspieces, it's still going to weigh around 12 pounds per foot or 100 pounds MINIMUM for an 8' section.
best thing to do is see what some of the other ramps are like. This whole calculation is so dependent on the situation that trial pieces will be necessary to get the best balance between weight and strength.
Grant Erw>
Reply to
RoyJ
Really good and sensible advice, Roy. I already told homey I wanted nothing to do with building his ramps out of 3" channel. I also advised him to forget building them 8' long, to make them 11' long. - GWE
RoyJ wrote:
Reply to
Grant Erwin
Don't give up on the three inch channel too quickly. If I remember correctly the stress varies as the cube of the span. So think about having some supports that go from the ramp to the ground. The height adjustment so they are really supporting part of the load could be adjusting the height of the support or varying where the support attaches to the ramp. If you have two supports per ramp, then the span is less than 4 feet, and you gain a bit in that the support is not a simple support too.
Dan
Reply to
dcaster
Grant, my ramps are made out of 3/16" diamond plate steel, 10" wide on the inside, 4" deep channel. The previous owner used them to put a 743 Bobcat
Reply to
ATP*
rec.crafts.metalworking allowable uniform load for steel channel?
Grant: You might look in the "Machinery Handbook" if you have one available. Assuming an elastic modulous of 30,000,000, the formulas there indicate, for a beam 8 ft long with a 4000 lb load in the center, in pounds/sq.in and inches:
Channel max stress deflection 3 x 4.1 475247 12.45 3 x 5 412017 9.93 3 x 6 358208 8.04 4 x 5.4 339222 7.69 4 x 7.25 279883 5.66
The above is for the channel appearing as a u, ie, the 3 or 4 inch dimension parallel to the ground. Vertical to the ground is:
Channel max stress deflection 3 x 4.1 87272 1.47 3 x 5 77419 1.32 3 x 6 69565 1.19 4 x 5.4 49740 .63 4 x 7.25 41921 .53
Handy book, the Machinery Handbook.
Hul
Reply to
Hul Tytus

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