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SDPWS 4.3.6.4.1.1 and Equation 4.3-9 require that forces in collectors connecting shear wall segments (drag struts) be factored by the reciprocal of the opening coefficient Co. so the shear force used for drag strut calculations is
vmax = V / COSLi
SLi is the sum of the shear wall segments, adjusting for narrow segments as per 4.3.4.3.
Neglecting hold-down offsets and narrow segment adjustments, this becomes
vmax = v / Co
The Co factor is applied to both the diaphragm shear force and the segment design shear force when used in the drag strut force calculation.
For drag strut forces calculated with shear capacity, perforated wall capacity is vr Co , where vr is the tabulated capacity, so dividing by Co has the effect of using the shear strength unadjusted by Co and
vmax = vr
also neglecting offsets and segment length adjustments.
The Co adjustment is made in addition to other adjustments to drag strut forces for seismic design considerations