Built-up Column Compression Resistance

Built-up columns refers to structural elements composed of two or more lumber members, fastened together side by side with nails, bolts, or split rings. These columns are commonly used in light-frame construction and are typically made from the same grade and size of lumber as the wall framing, streamlining the construction process. This calculation is specific to nailed built-up columns, which are the most common type and easiest to construct. Other methods like bolted or split-ring connections should refer to Clause 6.5.5.4 of CSA O86.

When constructing nailed built-up columns, individual laminations must be securely fastened in a manner consistent with Figure 3.2 of the Wood Design Handbook, ensuring that the design resistances and formulas hold. Pre-drilling is recommended for larger nails to prevent splitting, although nailing can be omitted if the column is incorporated into a stud wall with sufficient naining between the sheathing and all laminations of the column.

Where the column is short, or where sheathing prevents buckling about the weak axis of the plies, Pr may calculated as the combined factored resistance of the individual pieces taken as independent members. This will provide a larger factored resistance than calculated from the formula given in the built-up column section. To enable this calculation, change the Restraint input from 'None' to 'Buckling Prevented about Weak Axis'

Nailing requirements: (a) spacing of nails along the member length shall not exceed six times the thickness of the thinnest piece and spacing perpendicular to the member length shall not exceed 20 times the nail diameter; (b) all nails shall penetrate through at least 3/4 of the thickness of the last individual piece and nails shall be driven alternately from either face of the built-up member along the length; and (c) when the individual pieces of the built-up member are wider than three times their thickness, there shall be at least two rows of nails across the member width.