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Rquired bolt size to support gantry

  1. May 18, 2013 #1
    Hello all,
    Just thinking of this in my head, and maybe over thinking it. First a description of the problem,If i have two upright I beams, and an I beam spanning from one to the other. The horizontal beam isnt sitting on top of the two uprights, but bolted to the face of them. In calculating the force acting downwards at each end of the horizontal beam, do i just treat this as a simply supported at both ends and calculate the upward reactions at each, and use this as the force to calculate the shear stress in the bolts.
    Thanks in advance for all replies
     
  2. jcsd
  3. May 18, 2013 #2

    SteamKing

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    If you have more than one bolt at each end of the horizontal beam, the reactions on the bolts will combine in part to develop a reactive moment to whatever load is present on the cross member; i.e. the cross member will not be free to rotate, and a simple support condition (slope = deflection = 0) cannot exist.

    There are specialized codes and design procedures for selecting bolts and working out the connection details. If you are not an engineer, it is recommended that you consult one to make sure your connections are safe.
     
  4. May 18, 2013 #3

    SteamKing

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    Correction: The simple support condition is deflection = 0, but the slope is not equal to zero.
    In order for a bolted, rigid (or fixed) connection to exist, then deflection = slope = 0.
     
  5. May 18, 2013 #4
    My 2 cents.

    I'd treat it as a beam fixed on both ends. http://en.wikipedia.org/wiki/Fixed_end_moment

    The bolts should not see a shear load. If your bolts see any meaningful amount of shear, the joint has basically failed. They should only be in tension. The friction of the joint interface is what resists the shear force. When the beam is loaded, it's deflection will put additional tensile stress on the bolts.

    So first and foremost, I'd look at the friction forces needed at the interface.
     
  6. May 18, 2013 #5
    Thanks for your replies,
    Why will the slope not be equal to zero, when the deflection is zero?
     
  7. May 18, 2013 #6

    SteamKing

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    To be clear, for a simply supported condition at the ends of the cross member, the deflection will be zero but the slope at the ends cannot be zero since there is nothing the restrain the rotation of the beam at the ends.

    If the joint were truly simply supported at the ends of the cross member, there would be nothing which could keep the ends from rotating when a load was applied to the cross member. It's like placing a board across two saw horses, where the board overhangs each saw horse: If you put a load in the middle of the board, the board drops under the load and the ends of the board come up at either end. If you want to make the slope at the ends equal to zero, you must either clamp the ends of the board or put additional loads outside of the saw horses to create an additional bending moment which brings the slope at each saw horse back to the horizontal.
     
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