Simpson MST type strap installed over gypboard
Simpson MST type strap installed over gypboard
(OP)
Does anyone know of design values or test info on
Simpson MST type strap installed over gypboard.
Simpson will only give a value for their nail and/or
their strap when applied over wood framing (DF,SYP,SPF)
What reduction should be taken when a strap is applied
over sheetrock which is applied to CDX shear panel which is applied to 16"oc DF framing.
The length of the nail has been increased 5/8"+ to achieve full penetration into wood.
Simpson MST type strap installed over gypboard.
Simpson will only give a value for their nail and/or
their strap when applied over wood framing (DF,SYP,SPF)
What reduction should be taken when a strap is applied
over sheetrock which is applied to CDX shear panel which is applied to 16"oc DF framing.
The length of the nail has been increased 5/8"+ to achieve full penetration into wood.






RE: Simpson MST type strap installed over gypboard
Suppliers such as Simpson do not rate such an application because of the potential to develop out of plane bending when the drywall doesn't keep the anchor flat because of localized crushing of the drywall.
Why not cut out the drywall under the anchor and replace with wood blocking of the same thickness? This will keep the manufacturer involved in the event of a failure because you are using their product in accordance with their instructions.
Another approach, if you want to take on the liability, is to downrate the capacity of the anchor based on the bending of the nails as compared to just shear in the nails. Compute the bending stresses, compare the load required to bend to the load required to fail in shear and reduce capacity by that ratio.
RE: Simpson MST type strap installed over gypboard
One supplemental thought...if you cut out the drywall, why not just attach the anchor to the supporting sheathing/studs. You could then re-patch over the slot that you made to re-finish the wall.
RE: Simpson MST type strap installed over gypboard
Additionally: Wall panel manufacturers are looking for non-reduction solution since they prefer to pre-fab shear-ply and gyp-over without pre-strapping (shipping/alignment problems).
RE: Simpson MST type strap installed over gypboard