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RE: Tapered Steel Beam

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Web doubler plates for shear reinforcement are a common means of reinforcing webs in high shear zones, so the added plates should be acceptable.  The plates at the edges of the flanges, assuming adequate welds, should behave no differently than the webs of a box section that is used as a beam.  Shear flow (VQ/It) doesn't distinguish the transverse location of the web.  My greatest concern would be the point 74"+/- from the end of the beam where the flange is bent.  Is the bent flange to be the tension or compression flange?  If the web is cut to a point, the bending will likely create a radius smaller than AISC's minimum cold bend diameter.  If the extra web plates are carried to the same point and the weld terminated there, then you have a stress raiser at a point of strain hardening.  This could cause a crack in the steel, especially if the flange in question is the tension flange.  A flange cover plate to lower the stress at this point may be advisable.
 

Gordon Glass
Burgess & Niple, Ltd.
220 Lexington Green Circle, Suite 110
Lexington, KY 40503
Phone: 859-273-0557
FAX: 859-273-3332
gglass(--nospam--at)burnip.com

-----Original Message-----
From: Bill Marczewski [mailto:bill(--nospam--at)bsmstructural.com]
Sent: Wednesday, June 04, 2003 2:11 AM
To: SEAINT
Subject: Tapered Steel Beam

A local steel fabricator has asked me to approve a beam spanning 56’-0” (w21x147) that was sized by others and needs to have a pie-shaped section of the web removed.  The web will be cut down in height to as little as 12” remaining at the end, with a diagonal slope extending for 74” along the longitudinal axis of the beam.  The fabricator would like to cut this pie-shaped section out of the web, fold the top flange down along the new diagonal web and weld it in this location.  Assuming the beam was sized correctly for the loading conditions (by others) my thoughts are that shear will control the design with this new beam (I haven’t actually run the numbers yet).  My questions to the list are does anybody see any harm in performing the web modification as described?  Is this a poor technique and if so, what is a better recommendation?  I’m guessing I’ll have a lack of web material to carry the shear force and the fabricator has suggested adding additional vertical plates between the tapered flanges but showed them at the edge of the flange and not immediately adjacent to the beam web.  Has anybody done this before?  Any specific comments related to weld preparations and/or procedures that are specific to this application are appreciated.  Thanks in advance.

 

 

 

Bill S. Marczewski, P.E.

BSM Structural, LLC

Astoria, Oregon