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RE: Mixing Bolt Diameters

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>Does AISC have any requirements with regard to
>mixing bolt sizes in the same connection? I know
>there are restrictions about mixing bearing, slip
>critical and welds in the same connection but
>what about different sizes?

I don't know of anything that permits or prohibits this. As a general rule,
I do not think it is a good idea, but perhaps it depends upon the
application and what loads are shared and not shared.

Mixing bolt diameters in a shear connection would probably not work. How
would the connection know how to send more load to the stronger bolts? This
same idea would apply to any group of bolts sharing load equally.

Mixing bolt diameters in a more complex connection where there is shear
transferred by some of the bolts and tension forces transmitted by others
would likely be OK, as long as the bolt groups have consistent bolt sizes.
Or maybe some of the other bolts are not for load considerations. For
example, if a moment end-plate connection is designed with all of the moment
and shear carried by the flange bolts of a consistent diameter and smaller
diameter bolts are used to pull up the middle of a deep connection, I don't
think that would be a problem. I suppose one could also come up with
eccentric load cases where the bolt diameters could vary and be acceptable.

Hope this helps.


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