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Re[2]: Reinforcing Wooden Beams

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These are fundamental design considerations that one would find in a
strength
of materials text. It is the connection that is most likely to be the
failure
point in wood. Any reference that specifically addresses the transfer of
the
forces from the steel (or wood) reinforcing plate into the existing beam ?
Assuming that the reinforcing plate extends out to beyond the location
where
the existing beam is capable of resisting the loads alone and that all the
lag or thru-bolts are in this region at each end of the plate and not
uniformly distributed along the length of the plate, what is the basis for
designing this connection ? It is certainly not just the shear that exists
at
this location. I've seen used the individual tension and compression
resultants that correspond to the *peak* bending stress in the reinforcing
plate for design of a line of connection bolts along the upper half to
resist
the tension resultant and another line of bolts along the lower upper half
to
resist the compression resultant (which is equal to the tension resultant),
but I am not sure about this. Again any references that address this
connection design ?






______________________________ Reply Separator
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Subject: RE: Reinforcing Wooden Beams
Author:  seaint(--nospam--at)seaint.org (bob.ross(--nospam--at)wgint.com (Bob Ross)) at ROH
Date:    10/18/2001 7:18 PM





Ditto. I've used the same/similar approach.

-----Original Message-----
From: John MacLean [mailto:john_maclean(--nospam--at)pomeroy.ca]
Sent: Thursday, October 18, 2001 3:28 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Reinforcing Wooden Beams


<I am looking for a good reference that covers the subject of how to
reinforce existing wooden beams with steel plates. I'll appreciate any
help.>

I don't have any references but if I were doing it I would:

1.    Use modular ratio to convert wood to steel (multiply width of beam by
Ewood/Esteel).
2.    Calculate section properties I and Qs at centroid of the composite
section and at the steel to wood interface for composite section using area
of steel and converted area of wood.
3.    Check flexural stresses in steel and wood of composite section (My/I)
considering compression buckling in steel plate (i.e. how often would it
have to be connected to the wood to prevent buckling). Stress in  wood be
Ewood/Esteel times the calculated stress in the appropriate point in the
composite section.
4.    Check shear stresses in composite section (shear flow is
VQcentroid/Icomp) If steel is reinforcing the flanges only this might
result
in high shear stress in the web of the wood beam. You might consider
reducing
the shear stress calculated using shear flow by a factor of 2/3 since
allowable shear stress in a wood beam is calculated using V/bd but peak
shear
stress at mid depth of a rectangular beam is actually 1.5 x V/bd. 5.
Calculate shear flow between steel and wood and design connectors
accordingly
(probably shear plate connectors if the wood beam is heavy timber).
6.    Check deflection of composite section using Esteel Icomposite.

Hope that is some use,
John MacLean



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