Lag Screw Length

[dik]

This is for Canadian engineers that use CSA O86 mostly.

I’m writing an SMath program to design lag screws. I don’t usually design in wood and have a couple of questions. I’m using the Canadian Wood Code CSA O86-14. For withdrawal it appears that the effective length of thread is used. This makes sense. For lateral loads, I cannot determine if the length is based on the effective length of thread or the length of penetration is used. The description of the variables is a ‘little fuzzy’. Any clarification would be appreciated. Thanks in advance.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Phil1934]

Lateral is in the NDS where they don't differentiate between bolts and lags so take the embedded length. You might enjoy this.

https://www.awc.org/codes-standards/calculators-software/connectioncalc

 

[dik]

Thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I've got a note in to CSA regarding Wood Code issues. A couple of things:

They spec lag screws to SAE J429, Grade 1 and stipulate a yield strength of 310 MPa which is 45 Ksi. Portland bolt stipulates SAE J429, Grade 1 at fy = 36 Ksi.

The other query is if they have a series of formulae to calculate J[sub]G[/sub], the value similar but greatly different than NDS's C[sub]g[/sub]. NDS has a great calculation for this... it's complicated and I wouldn't want to do it by hand... but, it's easily programmable.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[skeletron]

For the lateral loads (if we are talking about the a through g unit shear equations)
I interpret it as "penetration into the member". So for the side member it is generally full depth of the side member and then the point side member is the left over length (Lp). I think there is an upper limit applied too, if you read a little back in Clause 12 of the code. Something like 8d vs 9d etc... My understanding is that the dowel-equations used in the derivation found that the stiffness doesn't increase beyond a certain length.

Not sure if this helps or confuses. It does take a bit of back-and-forth page flipping in the code and some Commentary reading. Still...it could be clearer.

 

[dik]

The max penetration varies with the species... thanks skeletron... pretty much what I've done... currently hung up on the J[sub]G[/sub] coefficient. Almost done. I had no idea that a simple lag screw was so complicated. Wood code way over the line.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Brad805]

I can't imagine lags are all that popular anymore. GRK and Simpson SDS screws are far more efficient.

 

[skeletron]

@Brad805: I agree. GRK, SDS, etc. are way better solutions especially since they don't require pre-drilling or manual turning, and are higher strength. I *think* O86 still requires you to check them using the "lag screw" equations as opposed to "wood screw" equations. I don't understand why, but I have observed some significant drops in capacity. Most people seem to just turn to the supplier tables which only really cover ledger situations IME.

 

[dik]

Not my circus, not my monkeys... they are as spec'd. I have a problem to sort out... and it's always bothered me a bit when I can't solve a problem... even as a kid.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik