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Splicing plies in span in multiply wood beam

Splicing plies in span in multiply wood beam

(OP)
Anyone here who specializes in structural design of wood, who can tell me what the "standard practice" is with respect to how butt joints in a 4-ply built-up top loaded continuous wood beam are designed if they occur within span at about 0.25 of the span?

Is the beam designed as though each ply resists an equal share of the load? Or is the strength downrated to something less? I realize of course that the strength has to be checked at the butt location based on only the continuous plies.

Other than the Alberta Building Code, is there any "Standard" or "Code" that deals with this? If so, what does it say about the strength?

Also, is any special nailing required?

RE: Splicing plies in span in multiply wood beam

(OP)
The Canadian Wood Council has responded to me and they say that it is standard practice to consider all 4 plies equally effective, provided OBC Clause 9.23.8.3 is complied with, inlcuding the somewhat more rigorous nailing.

I see OBC Clause 9.23.8.3 is similar to the Alberta Code Clause that BARetired referred me to earlier. So looks like BARetired (and perhaps others) was right!

(I remain a bit dubious of the prudence of this practice though, partly because the Canadian Wood Design Manual says that "Built-up beams are often used where the loading is light and dimension lumber is used for secondary framing, thus simplifying the type of materials required for the structure").

RE: Splicing plies in span in multiply wood beam

I think the key here is two fold:

1. The 1/4 point for the splices is basically very near the shear is zero for a uniform loading, and

2. The number of plies at the center span is sized for the maximum moment, and at the 1/4 point, for something less than that, requiring fewer continuous members across the splice.

Mike McCann, PE, SE (WA)


RE: Splicing plies in span in multiply wood beam

I always used the old UBC rationality "Any system or method of construction to be used shall be based on a rational analysis in accordance with well-established principles of mechanics..."

So if it meets this it is okay. If not I design it to meet it.

That is my "standard practice".

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Splicing plies in span in multiply wood beam

(OP)
It may be based on tests that may have been carried out.

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