# Rquired bolt size to support gantry

1. May 18, 2013

### blizzard95

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. May 18, 2013

### SteamKing

Staff Emeritus
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.

3. May 18, 2013

### SteamKing

Staff Emeritus
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.

4. May 18, 2013

### Jupiter6

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.

5. May 18, 2013