wood to wood moment connection

Have you looked into using plywood gusset plates instead of steel?

Even if you get the connection to take the moment, you probably won't be able to get it fixed, or to allow no rotation. Keep that in mind when you're checking deflection or any moment in your members that gets reduced by the connection you're looking at.

im thinking about not using anything. Just 2x12 to 2x12 with nails. The look out is not very long, probably only take about 700 ft lb. Any idea?

Here is the picture. How do I design the nail connection?

I feel that the flat 2x12 is taking most of the lookout load anyway, can I just say 6-10d and call it good?

Do an eccentric shear vector analysis. The force resisted by each fastener is:

1. The direct force = total shear divided by number of fasteners, plus

2. The eccentricity force = moment times distance from centroid of fastener group divided by polar moment of inertia of the fastener group.

can i just do the shearvalue of 10d nail single shear with 1 1/2 side member (from NDS) X number of nails X moment arm to the center of gravity of the nail group?

Visualize how the connection will behave when loaded with moment. The moment will cause the nail group to attempt to rotate. The nails farthest from the center will experience a large force that is nearly vertical. The nails closest to the center will experience a small force that is nearly horizontal.

Now consider the direct shear. Each nail will experience an equal vertical force.

Add the two effects together. The outermost nail feels the highest load because the moment effect and the shear effect are acting in nearly the same direction.

Look up elastic analysis of eccentrically-loaded bolt groups in any steel textbook. The principles are the same for the nail connection.

COE, I would use an elastic analysis method, easily found in a steel design book. Pick a minimum spacing for the nails and then find the configuration that produces the lowest [Σ]=(x[sup]2[/sup]+y[sup]2[/sup]).

Don't use the instaneous center of rotation method, if you come across in the steel book. You need empirical values for that, which you won't have.

When you have the nail shear from eccentric loading, you can check the deformation of the nail-wood system and figure your deflection and see if it's acceptable. That information is in the NDS, where you would need nail slip for calculate diaphragm or shear wall deflection.

Ive had this question come up with engineered lumber and have spoken to the engineering department of several manufacturers. They all advised me that you can not make a true moment connection with wood, at least with thier products.

If, by "true moment connection", you mean a connection that develops the full moment strength of the members and has stable hysteretic properties under dynamic loading, then I agree. Wood moment frames are not a recognized lateral system in most building codes.

But I wouldn't have a problem with using a moment connection to support a very short eave rafter like COEngineer is doing. As long as it is properly designed, that is.

"Wood moment frames are not a recognized lateral system in most building codes."
Yet enough timber portal framed buildings have been built to show that it is a viable construction method (in Australia anyway).

I designed a beam splice a while back to splice 2 x 8s if I recall correctly. I used 1" dia oak dowels in the design spaced about 4" apart in a staggered pattern. This was for a friend that wished to build a homemade pedestrian bridge for his kids behind his home in the woods for bikes. The span needed to be about 24 feet, but the lumber company said they only had 20 ft lumber, and that 24 ft lumber on special order would be more expensive. So in my case, the splice was quite close to the end, yet I needed about a dozen dowels in each connection.

Anyway, my point is I believe you can design a connection to transfer moment from one wooden piece to another. However, I would not use nails for it. I recommend either lag bolts, lag screws or wooden dowels. And make sure you check all the eccentricities in the problem.

The moment induced by your condition will be resisted by the moment of inertia of your fastener group.
I agree with UcfSE

COEngineer - sorry for the late post but this one looked interesting. Any long term moment connection in wood is a bad idea because eventually it will creep if it has any load on it. I have seen Glulam manufacutures use split rings and shear plates embedded in a tudor arch when they fabricate something they can't ship. They conviently put it where the moment is low, but they have a lot of material to work with.

I think your case would be better analyzed by using the nails you have shown as a pin connection, say at the center of the group. Add a metal strap, 2x4 or sheathing on top of the two chunks that were nailed to the flat rafter. If you connect the chunks together with this member, it will act as a tension member (at least for gravity loads). This will create a couple and thus work as a moment connection, at least for the small moment I would expect from your picture.

The best way to make a moment connection in wood is to figure out how not to make a moment connectin in wood.

Hmmm, looks "bouncy" from here. I'm conservative, but I would double up the cantilevered section of 2x12 (overhanging) and then specify a 1/2" plywood scab over those two pieces extending maybe 12" past the inside tip of your lookout 2x12. Use construction adhesive for all butted surfaces and nail it at 6" o.c. w/10d. I would also leave a 1/4" gap at the top edge of your outlooker 2x12 to account for any movement and rotation. You are saying 700 lbs. on the tertiary area for a single 2x12 with 6-10d nails or is that over a larger area and distributed to multiple outlookers ?