Sill plate question
Sill plate question
(OP)
Posted this in Structural forum with no response. This forum is actually more appropriate.
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?
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 question
Just a thought!
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Alternatively, you could nail a 2nd 2x4 on top of the sill plate to provide a doubler at each bolt. Drill through the sill plate and the doubler board. You will now have twice the shear strength at the connection, so 1/2 inch bolts should be OK.
Another solution would be to buy or make a metal "C" section to fit down onto the sill plate at each bolt. I have seen these for sale at hardware stores in the area where joist hangars and rafter ties are sold. If you can't find them, they would be easy to bend from flat sheet metal of medium gauge. Drill a hole in the center so it fits down over the bolt and the sill plate. The "C" takes out most of the side load and backs up the sill plate to help prevent it from splitting out under side loads.
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The NDS is a recommended guide not a code requirement.
RE: Sill plate question
Consider a 20psf wind load perpendicular to the wall. The shear on the anchor bolts, based on an 8' tall wall, would be 80 plf.
If the same wall had 1/2" ply nailed with 8d @ 6" oc, the shear on the anchor bolts could be as high as 260 plf, 3.25 times the load from out-of-plane loading.
So, since the primary function of the anchor bolts is to resist in-plane shear, you only need satisfy the 1.5D requirement.