NDS adjustment factor for 16d common nails inserted into end grain of wood joist loaed in shear?

[Engineerataltitude]

Does anyone know of any kind of adjustment factor to use with NDS Table 11N for nails connecting two wood members with the nail inserted through the side grain of the first member (deck rim) into the end grain of the second member (end of cantilevered deck joist). I need to evaluate this connection for the nails loaded in shear only. My attached guard detail 6 has a 2x rim attached to the end grain of a cantilevered deck joist. This connection has been challenged to demonstrate it can support the code required 200lb load applied vertically on the guard post, which translates down to the connection between the rim and the end of the deck joists. This would require that 6-16d's connecting the rim to the end of the joists can carry that 200 lb load. Seems like they should have that capacity. I can't find anything that addresses this though. I've used this connection for years, but never had this kind of challenge to it before. The NDS tables are clear that the table values are only for cases where both members have the nail axis perpendicular to the wood fibers. Of course nails into the end of a deck joist would not be that condition, but the only adjustment factors I can find to use with this table do not address the condition I'm dealing with.

Any ideas?

 

[fegenbush]

My recommendation would be to use a L-bracket similar to the one include in the link. Since the inspector is already challenging the detail I think the added expense is worth the reduced engineering time. Also, a recent deck collapse thread on this forum has shown this to be a common, but not necessarily structurally conservative, detail.

http://www.homedepot.com/p/Simpson-...Galvanized-Reinforcing-L-Angle-L70Z/100375233

 

[XR250]

Seems like a bad detail to count on, but they seem to perform adequately in my experience. I agree, adding and angle is a good solution. How are you dealing with the lateral on the guardrail?

 

[mike20793]

There is an end grain factor that can be applied when calculating the capacity of the nails. It should be applied when calculating the capacity rather than reading it out of a table and reducing it.

 

[Lomarandil]

Agreed, if you want to engineer it out, I would go back to the yield limit capacity equations (since this isn't a common connection detail, it's not in the tables), and the modify as necessary for the end grain condition.

Make sure to account for the minimum penetration too.

From what's shown in the sketch, I'm not sure it's a simple shear connection either. If it's supporting a guardrail, I'd at least check it for combined shear and withdrawal from the vertical and lateral handrail loads. And the Medeek part of me would want to consider additional withdrawal from the lateral guardrail load over that moment arm.

But in general, I'm with Fegen... I'd probably just add the bracket.

 

[Engineerataltitude]

For residential use, Code only requires the guard resist a 200 lb load applied in any direction to the whole rail assembly ( or 50 lb/ft lateral load if applies), no other load combination evaluation is required. So I've evaluated it for the point load applied laterally to the top of the post. This is resisted with bolts at the bottom of the post and a Simpson SP2 from the joist to the rim to keep it from peeling off.

Found what I was looking for last night. NDS 11.5.2.2 End Grain Factor of Ccg = 0.67 applied to the reference lateral design values Z found in Table 11N. 6-16d's holding the rim to the end of the deck joists has a capacity of 6(141 lb)(0.67) = 567 lb. Works

I know I could have added A35 of other angle brackets to address the plan checker's issue, but I really to wanted to know if this connection I've been using for 20+ yrs calcs out or not. Luckily it does.