Creating a Continuous Wood Beam By Sistering

[Corey7320]

I want to design a very long continuous wood beam for use as main girder of a 80' long pier structure. There will be two girders with floor beams spanning between the girders. I want to sister 3x10's that are 20'long and alternate splices at 1/4 points of 20' spans for the girders. I would like to know how to design the bolt pattern and spacing connecting the two sistered 3x10's. Is it just the shear in the beam that the bolts need to transfer? The shear flow equation VQ/I doesn't make sense to me in this instance since the two 3x10's have the same neutral axis. Also, i would like to design a cover plate bolted through the 3x10's at the splice of each 3x10 to handle the additional moment and shear that the continuous 3x10 alone can not handle at the 1/4 point. Any help is appreciated.

 

[SlideRuleEra]

Per the American Wood Council:
"There are no specific provisions for connections for built-up beams." See this link

http://www.awc.org/HelpOutreach/faq/FAQfiles/BeamConnections.html

Here is the document referenced:
"Details for Conventional Wood Frame Construction"

http://www.awc.org/pdf/WCD1-300.pdf

see pages 7 and 25

Suggest that you use at least 3 layers, not the 2 your have proposed. Using 2x10s would give you same nominal final thickness, but of course, it's the actual dimensions that are important. The multiple layers allow staggered joints, creating redundancy and giving the final assembled beam more uniform properties.

Here are a couple of documents of shear strength in wood:
"In-Place Shear Strength In Wood Beams"

http://www.fpl.fs.fed.us/documnts/pdf1998/ramme98b.pdf

and
"Recent (1996) Research On Shear Strength Of Wood Beams"

http://www.fpl.fs.fed.us/documnts/pdf1996/ramme96b.pdf

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