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Reinforcing Wooden Beams

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I can't provide you with any references, but I can tell you how I have 
handled the problem.

Connecting the plates to the wood beam means that both the wood and the beams 
have to deflect the same amount.  Therefore, the deflection of the wood and 
the steel has to be the same at each and every point.  (Method of consistent 
deformation.  Should be found in any strength of materials text book.)  
NOTE:  This is not composite design!

Assuming that the load that has to be supported is applied to the wood beam, 
then the problem is how much load (per unit length) has to be transmitted 
from the wood beam to the steel plate, which is obtainable by the above 

If you use bolts to connect the plate and beam, you can evaluate various bolt 
diameters; if you use shear plates, you can use the capacities of the 2-1/2" 
and 4" diameter shear plates, and get the required spacing.  I typically 
alternate the bolts at the top and bottom of the plates.  Shear plates 
require accurately drilled grooves (using a special tool) which is hard to 
obtain in the field, so they probably should be considered as a last resort.

The lateral buckling of the plate between bolts at the top of the steel plate 
needs to be investigated.  Therefore the plate thickness and required spacing 
of lateral support will contribute to determining the spacing of whatever 
connector you are using.

I try to make the plates as close to full length as I can, but, if the 
loading is uniform, partial length plates will still perform as a simply 
supported beam.  Therefore, the "end reactions" of the simply supported 
plates have to be carried into the wood beam.

Unless you have a *very* large wood beam, and *very* small plates, I have 
found that the plates will carry about 80 percent of the load applied to the 
wood beam after the plates are attached.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

THabaradas wrote:

. > 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.

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