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RE: notching a steel beam

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>If you take away most of one side of a top flange of a steel beam,

>say an 8" flange and on one side you notch out 3", what are some

>acceptable methods of reinforcement? There will be a pipe going

>through the notch, and I cannot do anything from the top. Is welding

>a plate of sufficient area to the underneath of the opposite flange ok?

>I see how this will replace the section modulus and compressive block

>that I am losing, but I am concerned with how the internal stresses of

>the beam "jump" from one side to the other.

 

A lot depends upon the details of the slab (if there is a slab) and the location of the material removed. The interconnection to the slab may be enough to handle any out-of-plane effects that develop due to the asymmetry. On a short segment, it is most important to extend the reinforcement beyond the zone of the cut to allow for the redistribution that has to occur from the full cross-section to the reduced and back to the full. Two ways I can think of to do this:

 

  1. Consider the situation analogous to shear lag in a tension member that is connected at some but not all of the parts of the cross-section and use a 1-x/L calculation to determine the length to extend the reinforcement beyond the zone of the cut.
  2. Pretend there are splices to be designed at each edge of the cut zone to connect it into the full member. Determine the force to be transferred and determine the length of flange/weld needed to do so. That will then tell you how long to extend the reinforcement.

 

My guess without running any numbers is that these will work out to similar values.

 

If there is nothing helping you to restrain the out-of-plane effects on the beam please let me know and fax me a sketch so we can see what else might need to be done.

 

Charlie