NDS Group action factor on sloped member connections 1

[thedg1]

I have a wood framed sloped canopy roof (similar to a lean-to) from the side of a tilt-up panel, connected with steel knife plate using multiple thru-bolts. In trying to determine the group action factor, I ran accross the problem of determining the "cross sectional" areas of the members. Typically I use the smallest areas (vertical or horizontal, as opposed to diagonal), but I can't find anything difinitive in the NDS. Any suggestions?

 

[RARWOOD]

I am assuming by your question that the fasteners in the wood are loaded at an angle to the grain. If so I am not aware of any NDS provisions which address the calculation of a group action factor when the fasteners are loaded at an angle to the grain.

The NDS Commentary indicates that it is standard practice to use the group action factor calculated for parallel to the grain loading, for both parallel and perpendicular to the grain loading.

The justification for this practice is the fact that due to shrinkage concerns the use of more than two bolts loaded perpendicular to the grain is not very common.

Also you probably could follow the procedures for calculating geometry factors for shear plates loaded in end grain. If the load is at a 30 degree angle to the grain use the group action factor for parallel to the grain loading. If the load is at a 65 degree angle use the geometry factor for perpendicular to the grain loading.

If you have less than 3 fasteners perpendicular to grai, I won't spend a lot of time worry about it.

If you have more than 3 fasteners you will want to look at the connection to see if shrinkage of the wood member will cause problems.

Also you want to look at local stresses, in the fasteners group. See NDS section 10.1.2.