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Beam Equations

  1. Mar 18, 2010 #1
    I might be in the wrong place, let me know where to go [kindly, ha] if I am.

    I havn't had math and physics etc since 1956 and never had the course "Strength of Materials"; I have a beam equation that I'd like answers to; it's not for a test, nor anything but my info, and I'd like some help drawing a Shear Diagram, a Moment Diagram, then to find the max deflection value.

    If there is a more "Structural" forum that you know of, let me know. Else if I HAVE any takers here, let me know. The problem is not easy to diagram as I have no tools to DO IT. So it'll have to be all words, carefully presented.

    The beam is freely supported at each end and is 11.00 ft long.

    There are POINT loads [I don't want to approximate a uniformally loaded problem; I want it to be specific for these loads].

    In from the left end 0.5 ft is a load of 75 lbs, in 1.5 ft is a load of 70 lbs, in 2.5 ft is 65 lbs, in 3.5 ft is 60 lbs, in 4.5 ft is 55 lbs, and in 5.5 ft [the middle] is 50 lbs, then the loading is symetrical, starting in from the right, 0.5 ft is 75 lbs, in 1.5 ft is 70 lbs, etc; total load of 700 lbs if I can still add correctly. So of course then I'd have 350 lbs on each end, but I can't get STARTED to even find the Shear forces as they increase/decrease towards the middle, then of course, same thing on creating a Bending Moment Diagram and then, a deflection equation, please.

    If you can help, help me and thanks, if you've gotta send me away, do it kindly, ok?


    LarryR : )
  2. jcsd
  3. Mar 18, 2010 #2
    If you could describe the beam is it an I beam? rectangular? you should sketch the details on a page and scan it and email it to me. I can then send you the solution.

    I could sort this whole problem out if you give me that. I presume if its a steel s275 beam yea?

    I can tell you already shear will not be a problem for an 11ft beam given that it has sufficient depth.

    The max shear on this beam is on the edges where it is being supported and the value of max shear is 350lbs.
  4. Mar 18, 2010 #3
    Don't laugh, but you can chuckle, ha. It's a 2 x 6, or 2 x 8 etc, so see, that is not part of the question. I'm wanting to learn how to create the shear diagram [even tho it's not gonna break; I just want to know HOW to do it]. Then once the shear diagram is created, I'm wanting to learn HOW to create the Moment diagram.

    So if it's a steel beam, joist, or a railroad tie, you see, I just want to know how to create those diagrams, then to find the deflection.

    I'll try to figure out how to email you. And I thank you for your willingness to help.

    LarryR : )

  5. Mar 18, 2010 #4
    alright no problem...its not too hard to make the shear and moment diagrams i have a good pdf that i downloaded from an american university called wisconsin i think? but its really good and explains fully how to create bending moment diagrams and shear force diagrams.

    i can email that to you.

    to quickly demonstrate in words like yourself how easy an SFD is a horizontal line represents the beam on the very left you draw a line straight up and mark it as 350lbs...

    as the max shear is on the edges and this is gotten by the (total load/2)

    moving in from the left end say 2 ft in you have a 50lbs weight then from your 350 line draw a line horizontally over until you reach where the 50lbs weight acts...

    Then a vertical line downwards to the value of 300lbs as the shear suffered by the beam by this weight acts down i.e. the shear values tend towards 0 as you get closer to midspan.

    bending moments however are a maximum at midspan!

    Essentially in this instance it will be a step like SFD...any way i dint know if im any use at explaining but the PDF has visual aids so it should do the trick for you...just need your email.
  6. Mar 18, 2010 #5


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    Homework Helper

    Here are links to some reference information that might help:


    http://oak.cats.ohiou.edu/~williar4/html/HapEd/NSF/Stat/Beam.pdf [Broken]

    http://ocw.mit.edu/NR/rdonlyres/Materials-Science-and-Engineering/3-11Mechanics-of-MaterialsFall1999/Modules/statics.pdf [Broken]
    Last edited by a moderator: May 4, 2017
  7. Mar 19, 2010 #6
    Thanks a million; that top one REALLY helped. Thanks to you and others that are emailing me, I'm beginning to get a grasp on it................. I'm graduating now to "overhung" loads, ha.

    Truly, thanks.

    LarryR : )
    Last edited by a moderator: May 4, 2017
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