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Thread: How many bolts are TOO many?

  1. #1
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    How many bolts are TOO many?

    Bolted Beam-Beam Connections.jpg

    Referring to the attached picture.

    I have been wondering how to calculate the number and placement of bolts in a bolted beam to beam connection.
    Obviously, the picture shows far too many;
    there are so many holes in the end of the beam that the beam itself will fail at the bolt 'line'.

    In thinking this through, assuming a vertical load only,
    it would seem that the maximum number of bolts needed
    is the minimum number that will resist the shear load on the bolts themselves.

    Right?
    Last edited by dalecyr; 03-31-2011 at 06:24 PM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    surprise2

    I think it is easy to design such that the bolts shear strength is greater than the bolted material. Grade five steel bolts are way stronger than A36 or other structural steel.

    See the attachment I put in this post for a little guidance..
    Attached Files Attached Files

  3. #3
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    Ah, thank you.

    A very informative document.

  4. #4
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    Dale,

    Kelly has you pretty much on the right road, the only thing I would adjust with Kelly's comment is I would change it to, "the bolt's yield strength."

    By that I mean, that if you were supporting something with the bolts mounted vertically then the bolt failure will be in tension. If you had say a mezzanine floor supported from above by vertical columns with end plates the bolts will be in tension. Obviously it would be better to design the thing so that the bolts are in shear as that is the strongest connection for a given bolt diameter and load. But, should the bolts have to be in tension, then so be it. The number of bolts required and thus their spacing will be determined by their tensile strength.

    Another rule of thumb to consider for bolt spacing is that the yield strength of the material remaining between each bolt should be at least 30% (more is better, I never go below 50%) greater than the yield of the bolt. If the bolt spacing is too close then the connection plates need to be made larger or the design approached from a different concept.

    Bolt size, strength and spacings tend to design themselves based on the load, once all the failure considerations are taken into account.

    Dave
    Last edited by PinkertonD; 04-01-2011 at 10:01 AM. Reason: Added name

  5. #5
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    Thank you.

  6. #6
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    what think to use grade 8 yellow chromate finish

  7. #7
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    Alright, so I know how much force will be pulling on two sections (118kN) and I know the shear capacity of ONE bolt (514MPa) how do I put these together to find out how many bolts I'll need (I know how to do the arrangement, just not how to figure our how many bolts I'll need all up.

  8. #8
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    Quote Originally Posted by Kelly Bramble View Post
    I think it is easy to design such that the bolts shear strength is greater than the bolted material. Grade five steel bolts are way stronger than A36 or other structural steel.

    See the attachment I put in this post for a little guidance..
    Kelly - where did this reference come from? Looks like a good source for mechanical design, I may want the rest of that book.

  9. #9
    Principle Engineer
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    "In thinking this through, assuming a vertical load only,
    it would seem that the maximum number of bolts needed
    is the minimum number that will resist the shear load on the bolts themselves."


    For this scenario, I would agree with that statement and add that you need at least 2 bolts. But you have other forces and moments to consider and they would generally cause shear or tension that may well exceed the pure shear scenario.

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