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RE: Reinforcing Existing Beam

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You might want to consider jacking from the new low beam.  This will preload
the new beam and reduce the initial stress on the existing beam.  You will
also have to calculate the horizontal shear to size the WT connectors and
the welds.

1.  Install the low beam
2.  Apply a load using a hydraulic jack and load cell
3.  Weld a pair of WT's in the space to lock the preload and provide
composite action.

Harold Sprague
The Neenan Company

-----Original Message-----
From: Rehan.Nawab(--nospam--at) [mailto:Rehan.Nawab(--nospam--at)]
Sent: Saturday, March 13, 1999 7:57 AM
To: seaint(--nospam--at); Rehan.Nawab(--nospam--at); structx(--nospam--at)
Subject: Reinforcing Existing Beam


          I am in a situation, where I have to reinforce an existing
          beam (18B40) while it is still carrying load.  The client
          requirement does not allow for welding cover plates.
          Therefore, I am opting to add a new WF beam to the existing
          beam using 3/4" A325 bolts.  This existing beam has full
          lateral support, i.e. Fb = 24 ksi.  This existing beam under
          existing loads is stressed to 18 ksi.  This only allows for
          approximately 6 ksi (18+6=24 ksi)  after adding the new
          beam.  Since, the new loads are heavy, this requires a very
          large composite section modulus to keep the stress around 6
          ksi.  In, this case W33x201 attached to 18B40.

          Is this approach overly conservative?  Is there any other
          way you would analyze the problem?  Existing beam is up-high
          and I don't think, I can have the beam jacked-up to unload
          the existing stress in the beam.

          Existing Moment = 100 ft-kip
          Combined Existing and New Moment = 385 ft-kip
          Composite Section Design Moment = 285 ft-kip
          Composite Section Modulus = 611 in3

          Any ideas?  Thanks in advance.

          Rehan Nawab, P.E.

          P.S. I posted this question yesterday, but it appears it got
          missed some how.