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Thread: I-Beam load capacity?

  1. #41
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    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

    Quote Originally Posted by martinw View Post
    Dear Pete,

    Presumably you thinking of arranging the beams "plank-wise"? Can you give any more information about the dimensions and properties of your beams?

    Best wishes,

    Martin




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    Default 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

    Kenneth Lerman
    55 Main Street
    Newtown, CT 06470


  3. #43
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    Quote Originally Posted by pstoop View Post
    ....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.

    An open mind is a virtue...so long as all the common sense has not leaked out.


  4. #44
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    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



  5. #45
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    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



  6. #46
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    Default Engineering Certification?

    Quote Originally Posted by martinw View Post
    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?
    Fork lift is already approved.
    If you cant afford the structural engineer, use the fork.


    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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I-Beam load capacity?

I-Beam load capacity?