huangyhg

wood to wood moment connection
can anyone guide me on how to design wood to wood moment connection without steel plate? i have this weird residential roof lookout structure where i have to splice the 2x12 roof rafters.
so its like 2x12 sloping 4/12, spliced with flat 2x12. i want to put nails in the area where the 2 rafter overlaps (diamond shape). i have never taken timber design class so... thanks!
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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
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
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=(x2+y2).
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

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