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Steel Beam Reinforcing

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Randy,

Your post left a few things unclear, but I hope that my "assumptions" will 
address them.

I am assuming that the existing beams will *not* be unloaded during the 
remodeling process, therefore stresses due to loading will exist in the 
original beam before any beam reinforcing is added.  Therefore, consideration 
of the existing (when modified) stress condition has to be taken into 
consideration.

I have never had very good luck in adding a cover plate or channel to one 
flange of a beam to take additional loading if the existing beam, unmodified, 
would be overloaded.  What I have observed is that although the section 
modulus is increased for one flange, the neutral axis is lowered, and the 
section modulus for the other flange is decreased.  Therefore, if the 
built-up section is designed based on the tension stress in the added 
reinforcing, the compressive stress in the top flange is going to increase 
due to the increase of its distance from the N.A.  If the top flange is 
overstressed under the new loading without modification, it will be 
overstressed a greater amount if reinforcing is added only to the bottom 
flange.

If it is possible, angles, bars, or plates welded to the underside of the the 
top flange could help offset the change in the N.A.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Randy Diviney wrote:

>>I have a few beams in an existing building that will be 40% overstressed
when new loading conditions are applied. I planned on using a channel
stitch welded to either side of the web to make up the difference in
required section modulus. The beams have adequate shear strength. I noticed
in our office standards book, we have a chart designed to reinforce beams
with rebar, welded to the top flanges.

My questions are:

1. Am I on the right track using channels?

2. Any better suggestions?

3. Any Internet sites or literature that deals with this?

4. Should I design the channel stitch welding for only the moment I expect
channels to carry

5. Will rebar really work?<<

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