I-Beam load capacity? - Page 4

1. Dear Pete,

Best wishes,

Martin

2. My engineering (???? lots of big questions marks because I am not an engineer) is done by seat-of-the-pants and gut feeling. And both of them are saying do not drive your five ton tractor, let alone your ten ton tractor over your three 10" I beam bridge at least until after you have written your will, assigned an executor and got all your affairs in order.

For bridges a good overload factor is maybe 5x so you should build something that can support a static load of 25 or 50 tons. That way when your 5 or 10 ton load bumps and bounces over it you do not overload it with the shock loads.

Find a reference website that will give you tables for the value of I for standard I beams and another site that gives you the formula for calculating the midpoint deflection of a simply supported beam and do the calculations. If your bridge is going to deflect more than about 1" with the 25 ton load I am not going to drive your tractor over it.

And if you don't know what I is or what a simply supported beam is don't build any bridges until you do.

3. Originally Posted by miljnor
dude!

It is legal to use even patented ideas for personal use!

I would never condone selling something that is a patented product (even if I disagreed with the patent issued)

copyrights however I have other opinions on!
What makes you think that you can legally "use patented ideas for personal use"? (And by the way, one can patent machines, one can patent methods, one cannot patent ideas.)

I'm not a lawyer, nor do a play one on TV; but I have interacted with patent lawyers.

Ken

4. Dear Pete,

Let's look at your bridge from another angle.

Is it a short piece of rough ground that needs to be a bit flatter for your tractor, or does is span a yawning 20 ft wide ravine that is 130 feet deep and has vertical walls??? If it is the latter, I personally would consider the consequences of structural failure a bit more seriously than if it was the former. (Mind you, a 5 ton load of metal and lumber toppling on to you even on a flat surface will probably have the same result).

End of party-pooper section....

OK, you say you have 3 12" deep I beams.

How wide are the top and bottom flanges, and how thick are they?

How thick is the web?

How far apart are the three beams, and what is the "deck" that forms the bridge?

Can you imagine a loading situation in which (say by driving the tractor in a wonky manner) only one of the three beams takes the load for a second or two.

Please do not get me wrong. I'm not trying to design your bridge, I'm just trying to find out if your beams are complete "no-hopers" or otherwise.

Best wishes,

Martin

5. Hi Martin,
These 3 beams are in standard "I" orientation, 10 inches high, 4 inches wide.
It is a 20 foot span, held at each end.
I pulled these out of my cousin's construction scrapyard, but they look like common steel extruction.
What I am interested in is the load capability per beam. For instance, what is the deflection for a two-ton midpoint load? If it is minimal, I know that my 3-beam bridge is safe for a 5-ton load with a one-ton wooden deck of 3x6 hemlock planks.

Thanks,
Pete

Originally Posted by martinw
Dear Pete,

Best wishes,

Martin

6. ## Get A Copy of BeamBoy

It's free. http://www.geocities.com/richgetze

I calculate a deflection of .31 inches at the center of the beam with a load of 4000 lbs. That's for an S10 x 25.4 beam. The beams in BeamBoy can be selected from a list of standard beams, or you can specify your own. S10 x 25.4 means that it is 10" deep and weighs 25.4 lbs per linear foot. That is the lightest 10" beam I saw listed.

Ken

7. Originally Posted by pstoop
....If it is minimal, I know that my 3-beam bridge is safe for a 5-ton load with a one-ton wooden deck of 3x6 hemlock planks.

Thanks,
Pete
No you do not.

When you drive anything over any bridge there is no way that the load is guaranteed to be distributed evenly. Your bridge has to be strong enough so that it can support your working load concentrated at any point on the bridge. In other words each beam needs to be able to support your working load individually then you may be able to conclude that it is safe.

8. you could also hang an extra trolly with threaded shaft hanging down. then tap a hole in plate welded to pipe. slide trolly where you want it and screw pipe down to extend to floor for extra support. when finished screw pipe up and slide it out of the way.
just my thoughts Dar

9. Dear Pete,

I guessed what the weight per foot was of your beam, and hand calculated that you would get a deflection at mid span of about 11mm (somewhere between 3/8" and 1/2". That is with a STATIC load of two tons at mid span.

OK, you may say, "I can live with that"...well err, no.

With a reasonably long and narrow beam, the top flange tends to buckle sideways under load, unless it is laterally constrained. In order to take this into account, the basic permissible bending stress for steel is reduced.

I did the bending stress calculation, and your beam will be asked to take twice the stress that it safely could .

Add to this the point raised by Geof about dynamic forces being considerably greater than the static one of two tons, and I would say you are in very dangerous territory indeed.

Sorry.

Best wishes,

Martin

10. ## Engineering Certification?

Originally Posted by martinw
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
Do factory inspectors look for engineering certification for cranes?
If you cant afford the structural engineer, use the fork.

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