diamond cut-outs in webs of these curved I-beams?

Discussion in 'Materials' started by Squidly-Diddly, Apr 7, 2020.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'm guessing its to mitigate bulging of web under heavy load. Surely its not just to save weight. Could it be "styling"??? Places to run wires/hoses or attach straps or other stuff???

    Why diamond(square) shape instead of round? Wouldn't sharp corners tend to concentrate stress VS rounded openings? Can't be that much, if any, harder to make round openings in steel.

    If to mitigate bulge in web during extreme load, is this ever used in ship building?, because I've never seen it.

    PS-object being transported not boat related, some forge sent to USSR in WW2 and now brought back because we don't make'em that big anymore.
     

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  2. Blueknarr
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    Blueknarr Senior Member

    I see reflective tape and no cutouts.
     
  3. BlueBell
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    BlueBell Ahhhhh...

    I see the cutouts.
    I believe they are decorative.
    Sure they lighten the load and are in a good place structurally but the effect is negligible.
     
  4. jehardiman
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    jehardiman Senior Member

    They are for weight savings and to look cool. Actually, there is very little stress except shear in the center of a loaded beam. The orientation of the cut-out (diamond to shear flow, not square to shear flow) causes about as much stress increase as a circular cut-out of the same size as long as the corner is properly radiused.
     
  5. Barry
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    Barry Senior Member

    shear flow.png stresses in beam.png


    The cut outs seem to quite small and often you will see this type of cut out in beams where you CAN reduce weight without compromising the strength of a beam.
    The right hand drawing, RHD, shows a simple supported beam.

    The loading produces:

    Bending stresses--- tension stresses in the bottom half (assume a symmetrical cross section) and equal compression stresses in the top half

    End support stesses----the total load divided by 2 will produce a vertical shear stress, . This would be vertical shear.

    Shear flow stresses- which are, in this case, horizontal stresses that occur at the neutral axis. The neutral axis would be the location, half way up, the tension stresses noted above are in contact with the compressive stresses, The
    Left Hand drawing shows Sliding of layers, Just assume that there are only two such layers. The point is that the beam must resist the sliding interaction between the upper and lower compression and tension
    portions of the beam

    Depending on the design, the beam could fail in any one of these conditions, depending on shape and material. For instance, the type of plywood floor joist with a thin web between an upper and lower 1 1/2 by 3 inch flange. While
    the joist experiences all of the above forces/stresses, if you were to cut holes in the web/plywood near the end supports, this beam could fail in vertical shear. That is the reason that when these joists are delivered to building sites, they
    come with instructions to plumbers, electricians, and hvac trades not to cut holes in the area close to the support.

    Normally, the material near the neutral axis would rarely fail due to shear stress as bending stress failures or even end support shear stresses would exceed the strength of the material. So you can at the neutral axis
    remove material with prudent calculations.

    As Squidly noted above, my first choice would have been round holes as the tip of the diamond, right at the tip will experience a higher stress concentration as compared to if they used a round hole

    Just a qualifier, the stresses that are mentioned above are not always exactly identical
    throughout the beam, Ie the bending compression/tension stresses are at a maximum at the outside edge of the beam. The vertical shear are max at the end supports and the max shear flow along the neutral axis. But when you are designing a beam, you normally work to calculate the loads, which produce stresses, then apply a factor of safety

    Another qualifier, I have taken some liberty to include Shear flow as a stress due to the units,
     
    Last edited: Apr 7, 2020
  6. Squidly-Diddly
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    Squidly-Diddly Senior Member

    if they are to "look cool" sure seems like they could've put some more stink in the style. Next time, give local Art Major $20. Given the application, sure seems like odd time to worrying about saving weight.
     

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  7. BlueBell
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    BlueBell Ahhhhh...

    Sight holes, I overlooked that possibility.
    (See what I did there, I made a pun...)
     
  8. jehardiman
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    jehardiman Senior Member

    That's art, not engineering...do you know how much drag that added.. and how much energy that wasted? The universe will never get that energy back. Somethings are just stupid from an sane engineering perspective...like no nuclear plants, but all cars electric. <roll eyes>
     
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  9. kapnD
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    kapnD Senior Member

    Well, the apprentices have to do something!
    Today’s exercise is the use of a diamond punch, precisely down the centerline and equally spaced.
     
  10. Blueknarr
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    Blueknarr Senior Member

    Changed screens
    Definitely decorative
    Although the ones on the lowboy portion might provide access to tie downs
     
  11. philSweet
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    philSweet Senior Member

    Now, bonus points, what did they do with all those squares? Are they all tabbed in there somewhere? Or did someone need a couple hundred plate steel targets for their firing range. The holes are handy for craning the bits around, I suppose.
     
  12. BlueBell
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    BlueBell Ahhhhh...

    Oh they're all hinged so you can close 'em up tight and look like a completely different rig.
    "Who me?"
     
  13. Barry
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    Barry Senior Member

    tie down holes, and sure enough the item in the picture shows a chain utilizing one of the holes, and hence the small hole, not a lightening hole and the upper notch allow that hook to settle into a specific point

    Would not like to pay the bill for 70 tires though
     
  14. fallguy
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    fallguy Senior Member

    If they made the low boy in China; every unneeded square inch of that beam would be cut out.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    When a structural member is subjected to transverse shear, not longitudinal shear, which is what Barry's post above is referring to, the maximum shear is vertical (or horizontal). The web can carry membrane tensile stresses in the longitudinal direction, as per Barry's images, but in the transverse direction no membrane tensile stresses can occur. This is the pure vertical shear experienced in the web.

    But, the shear stress induces equal tensile and compressive stress on planes that are at 45 degrees to the planes of the shear stress, like so:

    upload_2020-4-8_21-42-54.png

    So, looking at the beam's web, the cutouts mirror this pattern, with the cutouts being at 45 degrees to the horizontal/vertical.
     
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