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Built-up beams and columns are composed of two or more lumber members fastened together side by side with bolts or nails. Built-up members are often used in situations where the loading is light and dimension lumber is used for secondary framing, thus simplifying the type of materials required for the structure.
Notes:
1. WoodWorks Sizer assumes that there are no butt joints in a built-up member, except at beam supports.
2. Where possible, built-up beams should be top loaded and built-up columns loaded on the b-face. When side loaded, fastening between plies is more critical.
3. A repetitive member factor Cr, (= 1.15 for sawn lumber and glulam) is applied to built-up bending members with three or more plies if you specify that in the Beam Input view that it is a repetitive member. The default setting is to apply the factor as per NDS 4.3.9.
4. Except as noted below, cross-section properties are calculated as the sum of the properties of individual plies. For example, Sn = S x n, where Sn is the section modulus of the multi-ply member, S is the section modulus of one ply, and n is the number of plies.
5. The service condition factor for built-up Lumber, MSR and MEL materials is based on constituent member thickness rather than gross section thickness, because drying time depends on individual plies rather than gross section
6. For lateral stability calculations for the lateral stability factor CL in NDS 3.3.3.6, Sizer offers you the a Design Setting choice of whether to use the full member width or the single ply width as b in the expression for the slenderness ratio and in the limiting ratios for which the stability factor can be assumed to be 1.0. Research has shown that nailed and bolted beams have at most 30% composite action effect in terms of resisting torsional buckling, so it is recommended to use single ply width unless adhesives are used to laminate the members together.
7. The program always uses the single play width for the size factor CF or CV from NDS 4.3.6 and 5.3.6, respectively. This is because size factors are based on the variability of defects in the manufactured sizes of lumber (or lamination end joints in the rare case that more than one glulam member is built-up).