Wood Post Knife Plate Design 1

[Parkite]

Bottom Line up Front: How does one calculate the capacity of the bolt-wood interface for bolts going through a knife plate?

Background: An owner wants to connect a 10" post to the concrete footer using a knife plate. I have about 7500 lb (LFRD) uplift I need to chase through this connection. How do I go about sizing the bolts and the connection types? I just realized I only know the NDS Connection Tables (Table 12A - S). Using an internal knife plate and through bolts isn't one of the options in there (unless I am missing something).

Thank you all in advance.

 

[msquared48]

Each bolt is in shingle shear, twice, once on either side of the knife plate, bearing on the wood column through a hole of a certain length on either side of the knife plate.

No worries.

Mike McCann, PE, SE (WA)

 

[jdgengineer]

I do as Mike describes. I enter the NDS table with the wood beam width on either side of the plate and multiply capacity x 2. So a 6x I would use (5.5-.25) / 2 = 2.625 use 2.5 wood member. I'd also check the plate to make sure it is adequate as NDS table assumes 1/4" min and you effectively have 1/8" using this table simplification. Increase plate thickness as required.

 

[Deker]

If you want to get a bit more accurate than described above you can run through the yield limit equations in Table 12.3.1A. Or you can use this online calculator (Link). This is for 2005 NDS, though, so it might be a good idea to run through the equations at least once to verify.

 

[KootK]

The method described above is conservative, convenient, and common. That said, if required, I suspect that you could improve capacity by using the dowel shear equations appropriate to double shear (attached). Treating it as a pair of single shear shear problems, you're going to get more dowel rotation within the side members that you'll see in the real life condition where symmetry essentially creates fixity in the dowel at the middle of the connection. Fixity should create a more uniform -- and more favorable -- stress distribution within the timber either side of the plate.

The clip below shows how one might use the tool that Deker recommended to simulate the condition. No doubt your "side members" are thicker than 0.5".

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dik]

KootK
Great publication...
Dik

 

[KootK]

Thanks Dik. It is fun to see something of the wizard behind the dowel connection curtain.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.