Sources of Deflection at Shearwall Holdown Connections



	1, 2 and 6 do not apply to the PHD and HDQ. BP's are required by the City of Los Angeles. Check with your local building code on usage. (NDS section 11.1.2.3 requires a metal plate, metal strap, or minimum of a standard cut washer.)

Bolt slip can occur at holdown stud bolts.
Increased bolt slip can occur if oversized holes are drilled through the stud for holdown stud bolts (oversized holes are when the hole diameter is greater than the bolt diameter plus 1/16" per 2005 NDS 11.1.2).
When a holdown is installed on only one side of the stud, an eccentricity exists during loading which can cause more movement in the shearwall system.
Unrestrained anchor bolt nuts can spin loose during cyclic loading; using steel nylon locking nuts or thread adhesive may prevent nut spin.
Movement can occur when nuts are not tightened enough. Retightening bolts before covering wall may prevent this.
Deflection can occur in the holdown under load caused by stresses due to earthquake or high wind.
Lateral displacement at the top of the wall rotates the stud around its base causing the holdown base plate to displace vertically.
Wood shrinkage can occur due to drying of the sill plate, rim joist, and/or top plate; nuts may require retightening.
Uplift forces on the bolts can cause localized wood crushing at bolt bearing locations. Using larger bearing plates may prevent this.
Wood at the end of the studs (sill plates, rim joists, etc.) may crush under normal dead and live loading; additional compressive forces due to overturning during earthquake and high wind loads add to the deflection.