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Re: MQ/I

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Scott,

On one side of the theoretical cutoff point, there will exist flexural
stress in the original steel beam due to the moment at the location. On
the other side of the theoretical cutoff point, you would like that
stress to be distributed throughout the total depth of the composite
section. To get those stresses to flow from one section to the other you
need to extend the reinforcing past the theoretical cutoff point some
distance (see AISC pg. 5-38) and provide end welds to transfer this
force. I like to see an extension past the theoretical cutoff of twice
the depth of the tee, so that stresses can flow in a reasonable manner.

MQ/I is the average flexural force in the reinforcing or Mc/I x A, where
A is that of the reinforcing. (Q = A x c) A very conservative way to do
this is 21.6 ksi  x A. Simply take this end force (MQ/I)  and size your
end weld to transfer that force.

For further information, see AISC, 9th Edition Commentary pg. 5-132.

If the reinforcing runs to the end of a simple beam, M = 0 and
theoretically no end welds are required. I still, however, provide some
nominal end welds at that location.

Jim Kestner, P.E.
Green Bay, Wi.



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