CLT Handbook 3.3.1 and O86 8.4.3.2 - Effective Stiffness

Effective stiffness (EI)_eff is used bending moment resistance, calculation of panel deflection and vibration. It is calculated using the Shear Analogy Method, given in O86 8.4.3.2 and in the CLT Handbook 3.3.1, Equation 24.

EI_eff = b ( ∑ E_i t_i³/12 + ∑ E_i t_i z_i² ),

where the summation i is over all the layers for the major strength axis (longitudinal loading), and over all but the outermost layers for the minor strength axis (transverse loading), and

• t_i is the thickness of the layer
• For layers parallel to loading, E_i is the modulus of elasticity E as listed in PRG 320 Table A1
• For layers transverse to loading, E_i = E /30 (PRG 320, Table A1, Note d)
• z_i is the distance from the center of the layer to the neutral axis. For symmetric CLT panels, the neutral axis is the mid-point of the panel depth.

For fire-reduced sections, refer to CLT Handbook 8, Eqn. 8 - Effective Stiffness for Fire-reduced Sections.