As described in NDS 3.4 - Bending Members - Shear, for sawn, glulam, and SCL members, Sizer compares the factored allowable shear stress Fv' to the stress fcp due to the shear force V at a distance equal to the member depth d from the inner edge of each side of each support, which is equivalent to ignoring the effects of loads between that point and the support.
Sizer also identifies the unusual situation where the shear force is at its maximum interior to the span. It issues a screen warning and a note in the Shear Analysis diagram for this circumstances, and designs for the interior shear.
A different procedure using rolling shear resistance is used for CLT; refer to CLT Shear Resistance.
NDS Chapter 7 is used for I-Joists, for which Vr comes directly from the database for each section.
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