Bending Moment Design

Using O86 6.5.3.1 for sawn lumber, 7.5.6.5 for glulam, and 15.3.3.1 for SCL SIzer determines factored bending moment resistance with equations of the form

M_r = f F_bSK_zbK_L

• f = 0.9.
• F_b is the specified bending strength f_b multiplied by wet service, treatment, system, and load duration factors.
• S is the section modulus
• K_zb is a size factor defined differently for each material. Refer to Glulam Bending Moment Design and SCL Size Factors for more details.
• K_L is the lateral stability factor.Refer to Lateral Support and Beam Stability Factor KL and its subtopics for more details.

For glulam, K_zb and K_L are not applied simultaneously, the lesser value is used. Refer to Glulam Bending Moment Design for more details.

CLT moment resistance is calculated using and 8.4.3.2, and 15.2.3.1 is used for I-joists for which M_r comes directly from the database for each section.

Sizer compares the factored bending moment resistance M_r to the applied moment M at the point on the beam with the critical ratio M / M_r ratio. Sizer checks this ratio at the point of highest moment M in the interior of each span, and at the ends of the span.

For multi-span and cantilevered beams, both positive and negative bending moments are checked. If there is an interior notch, the bending moment resistance at the beam support uses the reduced section size to calculate M_r.

For rotated beams (oblique angle), the a moment resistance calculated for each axis using the section modulus in each direction. For SCL members separate f_bx and f_by resistances are used . Refer to Weak Axis Glulam Design for the glulam procedure.

The resistance calculated for each direction is then compared to the component of of the bending moment in that direction. Results for both directions are output.

I-joists and CLT cannot be rotated.