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RE: Steel Beam Reinforcing

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Roger,

You might want to review "Reinforcing Steel Members and the Effects of
Welding", by R. H. R. Tide, AISC Engineering Journal 4th Quarter 1990, and
some of the other works by Tide and Spraragen (referenced in Tide's paper).

Tide discusses at length reinforcing members both unloaded and loaded.  He
also presents several listed references.  After discussing reinforcing
issues with Mr. Tide several years ago and reading various references, my
practice has been to not worry too much about which component of a
reinforced element is stressed to yield and which ones are not stressed as
much.  I look more at the average stresses of the composite member.  As a
result, the initial stress in the parent member is not as important.  It
can't be totally ignored (like buckling), but it is not all that important.

When it comes to anticipated deflections, that is a different issue.

All of these issues came to a head several years ago when I had to reinforce
several trusses and beams that were highly stressed.  I did have occasion to
shore and relieve stress on some elements, but for the most part it was a
non-issue. 

The papers by Tide are much better than this meager synopsis.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Roger Turk [SMTP:73527.1356(--nospam--at)compuserve.com]
> Sent:	Wednesday, July 19, 2000 9:11 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Steel Beam Reinforcing
> 
> 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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