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Before searching through sections for a passing design, the program analyzes the member using an arbitrary stiffness, then adjusts the resulting deflections for actual stiffness of the candidate section, relying on the linear relationship between bending stiffness and deflection. This assumption does not hold for shear deflection, so the program approximates shear deflection for each section when performing the design search, then then when verifying the section in the Design Check, it calculates shear deflection rigorously.
It is possible, therefore, that a member which just barely passed the deflection check when searching for a design fails the Design Check, or that a section that would just barely pass the Design Check is passed over when searching for a passing section.
For SCL, shear deflection is approximated by the use of apparent E in the stiffness EI, and for CLT and I-joists by factoring the deflections based on a formula derived from uniform loading on simple spans. The deflection for this condition is given by
where w is the uniform line load and L is the span length. This is equivalent to using an effective stiffness equal to true EI divided by
When searching through candidate sections, Sizer adjusts the deflections calculated with the arbitrary stiffness to be those derived from effective stiffness rather than the true stiffness.