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Interpretation of CSA O86 Provisions
According to O86 11.8.1 for seismic design,
The sheathing-to-framing connections shall be designed to yield in mode c), d), e), or g) shown in Clause 12.9.3.2 for nails to ensure ductility in the shearwall and diaphragm.
The following statement appeared in O86-14, but was removed
The corresponding ductility-related seismic force modification factor, Rd, and system overstrength related force modification factor, Ro, for shearwalls are given in Table 11.8.1, provided failure is governed by sheathing-to-framing connection.
We have been informed that this latter statement was removed from the O86-19 in error, and we regard it as still in force. We have also confirmed that both these statements mean that when Rd and/or Ro are other than 1.0, shear walls that have brittle non-ductile critical design modes are considered to fail. These critical modes are either the nail resistance mode from O86 12.9.3.2 or when panel bending strength from 11.6.2.2.(b) governs over sheathing connection strength from 11.6.2.2.(a).
Shear Wall Design
For each wall design or candidate design for unknown parameters, the program records whether the lowest value of the nail failure modes for either side of the shear wall is not d, e or g, or when panel bucking governs and considers reports a failure in that case. The program passes over candidate designs with a non-ductile mode.
Design Results Output
If a completely specified wall fails because of the ductility check, the symbol # appears beside the wall capacity in the Shear Results table in the Design Results output and a note below the table indicates a design failure and the reason.
If the program cannot find a design after all unknown possibilities are exhausted, and at least one wall that had sufficient capacity was rejected because of ductility, the symbol @ appears by the wall capacity (which may appear to be a passing capacity) and a message below the table informs you what happened.
If any walls have a governing non-ductile mode, a line is output in the Design Summary giving the list of such walls
Detailed Shear Wall Design Output
The Detailed Shear Wall Design output shows the failure modes for each wall, with an asterisk by the governing one. It displays a note if there is a governing non-ductile failure mode. Priority is given to panel buckling failures if both criteria are non-ductile.