Shear Value for Drift Pin in 8x8 column

[keyPitsimplE]

I have done a fair bit of timber engineering, but I am not quite sure how to ACCURATELY calculate the shear value of an 8x8 HF2 p.t. post that has been spliced with a 7/8" diameter x 24" long threaded rod, embedded 12" into the center end of each abutting post.

My task is basically to develop a splice that will be as strong as the 8x8 post was unspliced. I have the moment connection taken care of with straps on all sides.

The post already has this 7/8" rod in the center, so I need to know what the shear value of it is.

If you cannot help me do this, please do not suggest other ways of making the connection. That is out of the question at the moment.

Thanks,

 

[SlideRuleEra]

Probably the best place to start is with the "General Dowel Equation for Calculating Lateral Connection Values". This is a free .pdf download from the American Wood Council, at this link:

http://www.awc.org/pdf/tr12.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[keyPitsimplE]

thank you very much! the impatient side of me was hoping to find a table or more direct route, but this is exactly where I need to start.

 

[keyPitsimplE]

I also found equation 12.2-3 in the 2001 NDS for square end cut split ring connections which is very similar. I just lacked the P & Q values for the threaded rod.

I'm making a spreadsheet for these equations (and the ones you provided above). If anyone knows of such a thing existing already, please let me know.

thanks

 

[civilperson]

Do not forget to include the exterior straps as contributing to the shear strength.

 

[keyPitsimplE]

I'm not sure if I can contribute any significant shear value from an MSTC66 strap. Maybe at most a value similar to an LTP4, around 400 lb for each strap being loaded in-plane???

So...I went through those god-awful General Dowel Equations and came up with a controlling Yield Mode IV, P = 4087 lb. After dividing by the Reduction Term, I got a Z = 1022 lb.

Can anyone verify that with a program, etc? That seems pretty low to me for the connection I described above. The shear capacity of an 8x8 HF2 post is about 6118 lb before duration factors.

I'm looking at a funky custom fab'd steel collar or something to develop the full shear capacity, unless I can get more value out of the dowel.

Thanks in advance.

 

[OldPaperMaker]

keyPitsimplE,
Just to make sure that I understand your situation, you have an 8x8 post that needs to be spliced butt end to butt end and that post splice has a shear and moment at the splice. Is that correct?
I don't think that the Yield Mode equations were intended to cover a dowel oriented parallel to the height of the post (column). I suppose that one could resolve the shear & moment at the splice into a couple and design connections to carry those loads. But, it is similar to splicing a laterally loaded beam in the middle of the span; it's just not a good idea.
You might want to check the Product Support Help Desk at

http://www.apawood.org

(253-620-7400) or AF&PA at

http://www.awc.org

to see if they have any suggestions.

By the way, I get the Fv from Table 4D of the NDS Supplement for Hem-Fir Post & Timbers as 140 psi. I think that gives an allowable shear of 5250 LBS before any Cd factors.

 

[keyPitsimplE]

Actually, I am trying to create a splice such that the post has the same or greater shear and moment capacity as if it were solid. I know it is not a good practice, but in my unique situation, it is the easiest way to please the City.

In the 2001 NDS, check out 11.3.2.4 and Table 11.3.2 which addresses a dowel inserted into end grain.

I got my shear value from the WoodWorks Sizer program output. I think it may have included some duration factors in the determination of the max shear capacity.

 

[msquared48]

I would consider installing four 1" wide bands around the ends of the columns - two at each 8X8. This could help prevent any lateral splitout of the 8X8 side from the lateral bearing of the dowel.

Mike McCann
MMC Engineering

 

[keyPitsimplE]

Mike,

I did consider that, but what then would you calculate to be the shear value of that dowel? I had to show numbers to the City.

 

[msquared48]

Good question.

I might consider using the P and Q values though for the shear in the longitudinal and transverse direction though with the banding in lieu of other research info. Maybe back off a little.

I would have to think about that one though as you obviously have.

Mike McCann
MMC Engineering