I-Beam load capacity?

[DennisCNC]

I know that there are a lot of factors to determine that exact number for load capacity of a I-beam, but is there a simple answer to this?

How tall, wide, thick will the I beam need to be to handle 3,000lbs or less and be supported on the ends only, 50 feet apart?

I looked at some formulas but it got confusing

Thanks

[Caprirs]

The formulas get confusing because they tend to calculate deflection and stress of the beam. To use the formulas, you have to determine what you consider "failure" of the beam. If it plastically deforms under the 3000lbs load? Can it deflect 1" in the center?

[jeffs555]

Do you mean actual load capacity, or are you concerned with deflection also? For most CNC applications, you are not concerned with load capacity because deflection will become excessive long before reaching maximum load capacity. Either way, you can download the free program BeamBoy to calculate stress and deflection. http://www.geocities.com/richgetze/

I am not really sure, but I believe the maximum bending stress for structural steel is around 20ksi. For a 50ft span, BeamBoy says it would take at least an S10x35 beam to stay under 20ksi with a 3000lb load, plus the distributed weight of the beam. The deflection with that load would be over 4 inches. At 35 lbs/ft that beam would weigh nearly a ton. What are you building?

[2muchstuff]

Sounds like he wants to put a beam across his shop and put a trolley on it to move machinery around.

[Geof]

Originally Posted by DennisCNC ...How tall, wide, thick will the I beam need to be to handle 3,000lbs or less and be supported on the ends only, 50 feet apart? Thanks

Approach the problem from the opposite direction. Find some standard I-beam profiles and the I value, that is the Moment of Inertia, for that profile then plug that into the formula along with your length and calculate the maximum deflection at the center. If the deflection is too much go to a bigger beam; bigger I and calculate again.

I can tell you 3,000 lbs in the center of a beam spanning 50 feet will require a hefty beam unless you can accept several inches of deflection.

[DennisCNC]

2muchdtuff, you got it. It can bend and deflect all it wants as long as it says near the roof and not on my head.

So a 12" I beam will do the trick to be on the safe side.

When I get the winch to the shop need to see if I will have enought hight for the trolly, winch, i-beam.

What about two smaller I-beams side by side?

[2muchstuff]

Years ago I had an engineer figure an I beam for my garage. He spec'd a 6" by 12" beam for a 24' span. With your 50' span I might want to go a little larger. As for the idea of side by side, I wouldn't. I'd weld the one on top of each other, this will give you less deflection.

Is it possible to support the center of the beam down from the roof or do you have an open steel truss girder arrangement holding up the roof deck.

[unterhaus]

I would think that at 50 feet, you are in the range of having buckling problems sideways as well as deflection problems. 2much is right, you should try to support it in the middle. Since the trolley will just ride on the lower flange, that leaves the upper flange free for support purposes.

And this is one application where going to an engineer that does these kind of things would pay off.

[BobWarfield]

Here is a thought. Rather than mounting a huge beam, can you make some A-Frame supports that travel as well? I haven't seen this done, but if you can position a travelling A-Frame either side of your hoist, you can ensure smooth travel over a 50 foot difference and only slightly more inconvenience (due to positioning the supports).

Best,

BW

[martinw]

Originally Posted by DennisCNC I know that there are a lot of factors to determine that exact number for load capacity of a I-beam, but is there a simple answer to this? How tall, wide, thick will the I beam need to be to handle 3,000lbs or less and be supported on the ends only, 50 feet apart? I looked at some formulas but it got confusing Thanks

Dear DennisCNC,

You say you want to handle 3000lbs, and the beams will be, I assume, "simply supported". Do you want to support 3000lbs at the middle of the span, or will it be distributed along its length. The loading conditions are completey different, and may call for different bits of steel. If you can give more information, I'll get out my text books.


Best wishes,

Martin

[DennisCNC]

^^ I measured the shop and it is 45' not 50' so thats a plus. I will use it move granite slabs around, from the cart to the saw and so on. Maybe my 3K lbs estimate is a little high. The slabs weight is 1,200lbs. max plus the winch, trolly, vacuum lifter, I think that will be another ~700lbs. So I think a better estimate would be 2,200 lbs. max load. This load will mostly be in the middle.
I can make the trolly support wheels farther apart to spread the load. If I happen to need to move something heavier i'll just use the forklift. With the over head crain one person can move the material around.

[martinw]

Originally Posted by DennisCNC ^^ I measured the shop and it is 45' not 50' so thats a plus. I will use it move granite slabs around, from the cart to the saw and so on. Maybe my 3K lbs estimate is a little high. The slabs weight is 1,200lbs. max plus the winch, trolly, vacuum lifter, I think that will be another ~700lbs. So I think a better estimate would be 2,200 lbs. max load. This load will mostly be in the middle. I can make the trolly support wheels farther apart to spread the load. If I happen to need to move something heavier i'll just use the forklift. With the over head crain one person can move the material around.

Dear Dennis,

unterhaus is right on the button with with comments on buckling.

If the top flange of the I beam is not restrained (ie prevented from moving sideways), and you have a clear span of 45 foot, the permissible bending stress for the beam will be far less that the nominal value for the steel. In order to get round this problem, you have to go for a larger section.

I have not done steel calculations for a while, but I thought I'd have a go.

My conclusion is that if the ends of the beam are not built in to something substantial, and if the top flange is not restrained, the major factor is keeping the bending stress to acceptable limits. If you have a beam of steel which has a basic permissible bending stress of about 23000 lbs per square inch, by the time you make allowances for the span and the lack of restraint, the actual bending stress that the beam can handle is down to about 6100 lbs per square inch under these conditions.

If my calculations are right (and it is possible they are not) you might consider this beam....

24" deep
9" wide

top and bottom flange thickness 11/16"
web thickness 7/16"
beam self weight 225 lbs per yard

The steel should have a basic permissible bending stress of at least 23000 lbs per square inch.

The total deflection at mid span (including that due to the self-weight of the beam) will only be a little over 1/4". The bending and shear stress are within limits but I have not checked for web crushing and buckling.

Finally, please don't go ahead and use this beam without getting a structural engineer to OK it. I can't afford the lawyers fees!

Best wishes

Martin