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Re: Steel beam--change of depth

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        Without knowing your code very well I would suggest that you consider an overlap such that the allowable web shear stress (for the web area between the two tension flanges) times the web thickness times the overlap length at least equal the full force in the bottom flange with the maximum load.  This may be a bit crude; but it should do it.
H. Daryl Richardson
----- Original Message -----
Sent: Wednesday, September 06, 2006 12:34 PM
Subject: Steel beam--change of depth

I have a project with existing steel roof girders (W27).  Due to vertical clearance requirements, we are placing a column at midspan, cutting off the bottom half of the girders, welding a new bottom flange plate on, and turning the W27's into heavy W14's.  As originally intended, this was to be full length of the girders; but the greater clearance is not required everywhere, and now the contractor is asking us to create details needed to scarf the bottom flange only in certain areas.  Thus, we will need to put a new bottom flange on in these areas which will overlap the existing bottom flange.  My question is, what should be this overlap distance?
I sized the new bottom flange to match the existing top flange; the stresses are relatively low (about 16 ksi of service-level bending stress).  Deflection is acceptable; shear stresses are low.  Can anyone direct me to a reference discussing the required overlap?  With 12 inches clear between the new and existing bottom flanges, I currently have settled on 24 inches of overlap as providing a gradual enough transition that I hope to avoid a vertical stiffener.  Does anyone know of an accepted technique to actually calculate this length?
Mike Hemstad
Minneapolis, Minnesota