1961 Laminate Wood Beams
1961 Laminate Wood Beams
(OP)
I have some existing 5 1/4" x 11 1/2" laminated wood beams in a project built in 1961 that need to be reinforced for increased loading. I am considering applying 3/4" structural plywood to the laminate beam sides and bottom for added width and depth. Can anyone in engineering cyberland suggest a source for information on reinforcing the beams; glue types and nail patterns for the applied plywood to make it composite with the existing laminate beams in place? The original design drawings called for fb = 2,400 psi for the laminate beams, but I have no shop drawings on the actual beams to verify wood species and stress rating. Beam spans are 20' with 3' cantilever.






RE: 1961 Laminate Wood Beams
Where that plate is held against the timber by loading I have used timber rivets to secure it. If this is not the case, I am really not sure how you might fasten it if your timber section is not large enough for a through bolt. Perhaps you could have a custom channel made and screw through the sides?
If you plywood is CERTAINLY a higher grade, and you are comfortable with the fastening, there is no reason I can think of not to pursue your original plan. Just don't count on the glue!
Oh, and by the way, occasionally I hear engineers argue that nail built-up side plate secured beams were very common 100+ years ago. The problem is that in those beams the side plates were just to make two smaller beams composite; You're taking about the side plates being part of the structural member's longitudinal strength, a very different issue.
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: 1961 Laminate Wood Beams
Built up timber beams such as box beams typically only use ply for the webs, the flanges are solid or LVL.
I agree that glue shouldn't be relied on for strength in your application, but it can be used to minimise slip, as long as the correct glue is used.
RE: 1961 Laminate Wood Beams
Glue Laminated Beams
The span tables have this note:
total live load 40 psf
fiber stress in bending 2400 psi
modulus of elasticity 1,800,000 psi
deflection limitation 1/360 of beam span
RE: 1961 Laminate Wood Beams
RE: 1961 Laminate Wood Beams
at a large enough curvature, radial reinforcement may become necessary.