I-Joist Design

Sizer uses a simplified design methodology for I-joists as follows:

• Specified moment resistance, shear resistance, 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. Custom versions of Sizer for individual manufactures like Nordic Engineered Wood include these features and bearing design.
• Sizer considers reduced deflections due to composite action between floor sheathing and the I-joists, by increasing the overall floor stiffness by 10%.

Shear Deflection

I-joists tend to deflect more than most solid sawn members due to shear deflection. The Sizer loads analysis calculates shear deflection using rigorous numerical analysis, using 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.

K is the shear constant value and EI is the stiffness, each stored in the database for each product and L is the member length .