Allowable shearwall tollerance
Allowable shearwall tollerance
(OP)
I recently reviewed a single family residence that was near or within the path of a tornado. The door frames were out of plumb by as much as 3/8" in the in-plane direction of the shear wall. I was just wondering in anyone knew the allowable tollerance for a wall being out of plumb in the in plane direction. I looked in the IRC and was unable to find anything.
Also the roof was constructed with 2x6 rafters and ceiling joists at 16" oc and collar ties at 54" oc. There were a couple locations where the rafters appear to have raised. Can this be caused by the storm or did it likely occur during construction? Is is possible the panel edges aligned at that rafter and the sheathing had lifted?
Any help would be appreciated.
Also the roof was constructed with 2x6 rafters and ceiling joists at 16" oc and collar ties at 54" oc. There were a couple locations where the rafters appear to have raised. Can this be caused by the storm or did it likely occur during construction? Is is possible the panel edges aligned at that rafter and the sheathing had lifted?
Any help would be appreciated.






RE: Allowable shearwall tollerance
3/8'' seems a bit high unless you knew what it was before. Does the door still close?? What about drywall cracks? Do the windows still open, close and seal? If none of this is working correctly - that wall may be "wrecked"
RE: Allowable shearwall tollerance
I would like to include in my report an allowable tollerance if possible.
RE: Allowable shearwall tollerance
1. The lifting of the rafters was more likely than not due to the Tornado. Make sure there are holddown clips at the ends of each rafter.
2. If the shearwalls are all drywall, as with seismic, after one event, the effectiveness of the drywall is significantly reduced. Thus, for vibrational seismic forces, the allowable forces are halved. Having been that close to a Tornado and seen the vibrational forces, I would consider applying the same criteria and recommending the installation of plywood shear wall sheathing. Not really required by the code, but I would consider it good engineering judgement.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Allowable shearwall tollerance
I do not think that the relative deflection or distortion is the key here, but the structural integrity of the shearwall as evidenced by any damage to the nailing or rock is.
Is there any evidence that the walls tried to lift off the sill plate? If so, additional reinforcing needs to be added there too - in essence a good retrofit is warranted.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Allowable shearwall tollerance
"...In jurisdictions that enforce the IBC and IRC, the allowable loads are applicable for shear walls that resist wind and seismic loads in in Seismic Design Categories A, B, and C. As per AC04, Section 4.5.2, the allowable racking shear load was determined as the lowest value based upon the following criteria:
1. load at which a net horizontal deflection of 1/8" occurred;
2. ...
3. ..."
In that the 3/8" lateral distortion is permanent, the integrity and structural usefulness of the shear walls has been compromised.
Your call.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Allowable shearwall tollerance