Need Shearwall Nailing Schedule (table)

[RMorrison]

Lew,

There is a certain amount that is covered in the Code, but also a certain amount of professional judgment. For example, the UBC (on which the IRC is based, but I don't have IRC since it's not used here) allows a 3/8" plywood CDX panel, nailed 6" edge/12" field with 6d nails to handle 200 lbs/ft. However, an engineering firm, knowing that contractors often overdrive their nails in a significant number of cases, going through at least one ply of this 3-ply material (and thereby reducing the nailing strength by 1/3) might not even include 3/8" plywood on their schedules.

Instead, their minimum typical shear wall will be 5-ply w/ 8d nails, good for 260 lbs./ft. Now a Simpson A35 clip angle is good for 450 lbs. (per their catalog) when used to transfer roof diaphragm loads from the eave blocking to a top plate, say. So, for 260 lbs./ft., you'd need one A35 at least every 1.73'. (450 lbs./260 lbs/ft.), or at least every 21" approx. Normal blocking would be every 16" or 24" though, depending on rafter spacing. You could put one A35 at every block at 16" o.c.and that would work, but what if the rafters are 24" o.c.? Some engineering firms might choose to downgrade the maximum shear value for that wall type to 225 lbs/ft and accept the 24" A35 clip spacing, others might choose to specify a different and stronger connector as typical in the schedule and keep the 260 lbs value for that wall type. Still others might say that 24" is close enough to 21" and just live with it even though it doesn't precisely calc out.

Now aren't you glad you asked?