Conditions for KL = 1

For solid sawn lumber, and for SCL by reference from O86 15.3.3.1, O86 6.5.3.2.3 specifies specific support conditions for which K_L can be taken as 1, which depend on the depth-to-width ratio of the member. A Design Setting allows you to indicate whether these conditions are met for your member.

For solid sawn lumber and SCL members less than 4:1, K_L = 1 regardless of whether this setting is checked. The exceptions is multi-span members with unbraced interior supports, if they are have a ratio greater than 2.5 you cannot assume K_L = 1.

For solid with ratios greater than 9:1, you cannot assume K_L = 1 even if the setting is checked, as per 6.5.3.2.3.

If the setting is checked, a design note in the output indicates the specific support condition required for design with K_L = 1.

For glulam members and built-up lumber members less than 2.5:1, K_L = 1 as per O86 7.5.6.3.1 for glulam and 6.5.3.2.2 and 6.5.3.2.4 for built-up lumber.

If K_L cannot be assumed to be 1, it must be calculated using 7.6.5.4, a glulam clause that also applies to sawn lumber and SLC via a reference in 6.5.3.2.2. Therefore, the following conditions lead to the K_L factor being calculated:

• For solid sawn lumber and SCL:
  • If the setting is not checked and the member has a depth-to-width ratio greater than 4:1,
  • If it is checked and either the ratio is greater than 9:1 or it is a multi-span member with ratio greater than 2.5:1 and interior supports not laterally supported
• For glulam and for built-up lumber or SCL members:
  • Members with a depth-to-width ratio greater than 2.5:1