(Simple?) I-Beam Load Question-------Please Help

[jaywitkow]

I have a portable gas generator that I want to drop into a hole in the ground for use during power outages. I have already bought a 1-ton trolley and a 1-ton hoist and I need to find an I-beam (or a T-Beam?) for a 10-ft span to mount the trolley hoist on. The generator weighs about 200 pounds and the hoist and trolley weigh maybe 50 pounds. It would be nice to have a 2:1 safety margin. Or, in otherwords find an I-beam that could handle a load of 500 pounds.

There's a scrap dealer about 50 miles from my house who says he has lots of I-Beams to choose from. The question is, what do I look for? I have no mechanical restrictions for the I-beam other than I would like to have it light enough that 2 guys could lift it.

I know nothing at all about this sort of thing, but my intuition tells me that almost any I-Beam that I'm likely to find would handle a load of 250-500 pounds over a span of 10 feet. Is this true? Does anyone have any advice to help me select an I-beam/T-beam?

Thanks in advance.

[Larry Jaques]

On 5 Jul 2006 20:20:53 -0700, with neither quill nor qualm, [e-mail] quickly quoth:

Your generator is likely lighter than any ten feet of steel I-beam which will support it. You might try aluminum. Why the 10' span?

Got math?

Try looking here:

sure you plug in how you're attaching it for valid results. G'luck!

P.S: I hope the hole is WELL drained and provides a snorkel for clear air to the engine, etc. Are you routing the exhaust through a gravel pit for noise reduction? I love seeing how folks end up doing things.

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[Doug Miller]

Not a problem. They don't make steel I-beams small enough that you'd need to worry.

Really.

Au contraire. You have to get up to _at_least_ a seven-inch I-beam before you see weights of 20 pounds per foot.

The smallest standard I-beam made is a 3" beam weighing 5.7 pounds per foot, a ten-foot span of which obviously weighs 57 pounds -- and can support a load of

907 pounds concentrated at the center. (The load capacity is higher still, if the load is near one end instead of in the center of the span.)

Beam supported at ends - concentrated load at center W[max] = 4fS/L, where: f = extreme fiber stress, taken to be 16000 lb/in^2 for structural steel S = section modulus of 3" beam, 5.7 lb/ft = 1.7 in^3 L = length of span in inches = 120 in this case [Carnegie Pocket Companion (23rd Ed.), Carnegie Steel Co, Pittsburgh 1923]

W[max] = 4 * 16000 * 1.7 / 120 = 906.67 lb

[Michael Daly]

16ksi is pretty low by today's standards. That's an implied safety factor of 2 to 2.5 or more, depending on your steel source.

And that's probably why. Your friendly neighbourhood library may have a more modern source for structural steel properties.

Mike

[Doug Miller]

OK, fine -- since that's in the *numerator* of the load calculation, a higher value means an even greater maximum load than I calculated. The point remains that a three-inch I-beam weighing less than sixty pounds is easily capable of supporting *much* more than the 250 lbs the OP wishes to.

[jaywitkow]

Thanks a lot for the numbers. I spent about 4 hours last night researching the calculations and came up with about 90% of it, I think. So, I'll file these away for future use. As it turns out, I drove 50 miles to steel salvage yard and forgot my notes on minimum span for the trolley. So, I missed out on a great deal for $25 on a 3" I-beam. The beam was 2 1/2" wide and I wasn't sure it would fit.

When you go to these scrap yards you just have to rummage around and take what they have. What I wound up buying was to 3.5" angles. I'm going to bolt them together and make a "T" beam out of them. I'm sure they'll work OK, it's just going to involve the extra work of drilling some holes for the bolts.

As it turned out, by the way, the trolley is adjustable for widths of

2.5" to 8.0".

[Larry Jaques]

I shouldn't have -just- moved that piece of RR track in my shop that morning, huh? Mayhaps it's a bit heavier in profile, y'think?

-- Save the Endangered ROAD NARROWS! -|-

Ban SUVs today! -|- Full Service Websites

[jaywitkow]

Aluminum would be nice. I thought about it, but didn't know where to buy it and figured it would be too expensive.

The hole is 3 1/2' x 4 1/2' and the generator is only 25" x 30" and I'm hoping the generator noise sources will only have to be about 6" below the top of the hole. So, I'm assuming there will be plenty of air circulation without any modifications to the generator. I'm also hoping the hole will take care of all the noise reduction. There are a lot of things I'm not going to know until I actually test it. This has been an adventure and I'm not through yet.

The hole will have about 6 inches of gravel in the bottom and there will be a small roof about 6' above the hole. So, I don't anticipate a problem with water.

[Doug Miller]

Uhhhhh.... yeah. Railroad rails have a *much* heavier cross-section than I-beams.

[Pete C.]

At 200# it's unlikely to be a NG unit. Also at 200# it hardly requires an I beam gantry to move and lower.

Pete C.

[dpb]

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I think that's being _way_ overly optimistic unless you're in the Sahara...as somebody else already noted (J Meehan???), when you're most likely to need it is when you're also most likely to have had a downpour w/ high winds, etc. A roof over the hole itself may deflect the initial falling water from coming in directly, but that water has to go somewhere plus there's all the other groundwater. Of course, a berm around the edge can also help, but it really just seems like the hardest way possible to accomplish an objective...