Sill plate anchor requirement
Sill plate anchor requirement
(OP)
Have a basic question regarding wood sill plates for which I can't seem to track down an exact source. According to NDS Table 8.5.3 the minimum edge distance for a bolt loaded perpendicular to grain is 4D for loaded edge and 1.5D for unloaded edge. For a wall subjected to wind pressures (positive and negative directions), this 4D requirement technically prevents the use of 1/2" diameter bolts in a 2x4 sill plate, since half of 3.5 inches is less than 4D distance. Of course, 1/2" and even 5/8" bolts are commonly used as anchor bolts. Can anyone help clear up the apparent conflict?






RE: Sill plate anchor requirement
Anyway, if you've gotten further feedback, I'd love to hear it.
RE: Sill plate anchor requirement
RE: Sill plate anchor requirement
RE: Sill plate anchor requirement
I thought the 4D and 1.5D refered to all bolts in wood.
RE: Sill plate anchor requirement
DaveAtkins
RE: Sill plate anchor requirement
The NDS requirement of 4D and 1.5D is for bolting two members, main and side member (SEE Table 11.5.1A, NDS 2001 Edition, read all the print). IT DOES NOT REFER TO SILL PLATES BOLTED TO CONCRETE. If this were so than SIMPSON could not market their Strongwall panels, for they use 2- 7/8" and 4-5/8" bolts for a 2'-8" panel centered to the bottom plate for 2x4 walls.
What may I ask is the out of plane load at the foundation level?
RE: Sill plate anchor requirement
It appears I am just out of date, I have the 97 NDS and it specifically says that edge distance, end distance and spacing shall apply to bolts installed with concrete or steel as the "main or side member"
I believe that the loading that FSS was talking about is the wind load on the wall.
RE: Sill plate anchor requirement
For tall walls, or high thrust due to wind or other pressure, it can be a creative excercise to design the connection. Sill bolting may not provide enough in many cases.
RE: Sill plate anchor requirement
Section 8.5.4 refers to END distance, not EDGE distance.
DaveAtkins
RE: Sill plate anchor requirement
RE: Sill plate anchor requirement
If one wishes to obtain the proper reference for Sill or Bottom Plate Bolting requirements then it would be necessary to obtain the WFCM also produced and published by the American Forest & Paper Association.
Please see Tables 3.2 through Table 3.3A, 2001 WFCM, (depending on wind or seismic). This should clear up any misconceptions and the tables provide excellent reference and design values. Again, no edge distance requirement. And as in my earlier post max. 12" from and ends and min 7D.
Anyway, anyone involved in design of wood structures should have this manual if nothing else.
RE: Sill plate anchor requirement
The end and edge full value minimum distances are the same 4D for compression but 7D end distance for tension. See section 8.5.3 and 8.5.4.
The NDS in it's entirety is adapted into the IBC in section 2306.1.
RE: Sill plate anchor requirement
I don't agree that sill plates have some sort of special requirements for edge distances. These values are irrespective of the main member's material because we're concerned with local failure in the wood itself.
As for the reduction of strength method, referred to by AlohaBob, that only applies for loaded end distance, which is for loads parallel to the grain.
I would suggest modelling the structure as if the windward sill plate offers no resistance. Transfer the loads to the shear walls and make sure that they are strong enough.
Cheers,
Mike
RE: Sill plate anchor requirement
The shearwalls will carry three loads.
A shear load. This will be resisted at the plate by parallel to grain design bolt values. The edge is not loaded so the minimum 1.5D applies.
An out of plane load. Wind, seismic, or other. The shearwall being wood resists this load typically like a simple beam. The upper half load transfering into a diaphram at a floor, the lower through cross grain bearing on a bolted sill plate. Component wind loads have higher suction load than inward pressure. The shearwalls main function is a shearwall, but it still sees normal wall loads. This is where the issue of edge distance comes. I don't typically worry about it, the area that concerns me in this design limit is basement wall connections to floor diaphrams. It's too often neglected. The loads are higher, the plates splitting is a problem.
And Vertical.
Plate bolts don't typically address this. You use a holdown. I think Simpson got so popular because they designed their hardware with the 7D stud or post end distance and bolt spacing requirements incorporated right into the self jigging prefab hardware for tension. They meet code requirements and provide tested design values.
RE: Sill plate anchor requirement
Check out the WFCM:
http://www.awc.org/Standards/wfcm.html
Merry Christmas!
RE: Sill plate anchor requirement
This probably introduces new challenges, such as decreased anchor spacing or increased anchor diameter, but at least we have the means to comply with the current design standards and allow for construction tolerances on an exterior 2x4 wall sill plate.