Sizer uses a simplified design methodology for I-joists as follows:
Specified moment resistance Mr, shear resistance Vr and stiffness EI are defined directly in the database rather than being derived from specified strengths and section dimensions.
Sizer does not do bearing design for I-joists. Required bearing lengths are based on the supporting members only.
Sizer does not consider web holes, partial load combinations for web holes, web stiffeners, or web reinforcement.
Sizer considers reduced deflections due to composite action between floor sheathing and the I-joists, by increasing the overall floor stiffness by 10%. This is done after the calculations for shear stiffness are made.
I-joists are assumed to be fully laterally supported top and bottom, and are not designed for buckling effects.
Unlike solid cross-sections, shear is evaluated at the support instead of a distance from the support that equals the depth of the joist.
Shear Deflection
I-joists tend to deflect more than most solid sawn members due to shear deflection. Sizer calculates shear deflection using rigorous numerical analysis, with shear stiffness GA derived from the published shear constant K that is found in the WoodWorks database for each I-joist section. Shear deflection generally increases deflection by about 10%.
If the any of the input parameters are unknown at the start, Sizer uses an approximate method to calculate shear deflection in its search for passing designs, then the more rigorous method when a member is selected for a detailed Design Check.
