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The system factor KH is applied according to CSA 086 5.3.5 and 6.4.4 (Sawn lumber) , 7.4.4 (glulam) and 15.3.2.4 (SCL). In accordance with 8.3.4 and 1 5.2.2.4, the system factor for CLT and for I-joists is 1.0.
System factors are primarily intended for joist and wall stud members, but can be applied to beams if are spaced within 610 mm, or are built-up beams.
For all member types other than CLT panels and I-joists, you use the Load Sharing input to choose whether a system factor is to be applied. For sawn lumber joists, you indicate whether it is Case 1 or Case 2 load sharing; for all other member types you indicate Yes or No.
Case 1
For lumber construction systems defined as Case 1 systems, specified strengths are modified by a factor of 1.10. This applies to traditional lumber joist or stud systems with basic sheathing and fastenings.
Case 2
For Case 2 systems with certain combinations of sheathing and fastenings, larger values (up to 1.4) may be used. One way of achieving a Case 2 system for joists for example, is to ensure that the joists are sheathed with plywood or oriented strand board (OSB) of minimum 9.5mm (3/8 in.) thickness and that the sheathing or subfloor is attached by 2 in. common nails at 150mm (6 in.) on centre at panel edges, and at 300mm (12 in.) on centre elsewhere.
Solid Beams
For these, the default is No. You select Yes only if you know that the the beams are to be spaced not more than 610 mm apart. If so, the Case 1 KH factor from table 6.4.4 is applied for sawn lumber.
Built-up Beams
For sawn lumber, the default is Yes, as CSA O86 6.4.4.3 says that built-up beams with more than 2 plies have the factor applied. For SCL beams, the default is No because for many products, field-assembled beams do not qualify for the increase. A note to that effect appears in the output when the KH factor is applied. There have to be at least three plies for KH to apply.
Built-up Columns
For built-up columns and wall studs loaded in tension, when you select Case 2 Load Sharing as defined in 6.4.4.2, the program considers it a Case 1 situation and applies the system factor of 1.1. as Table 6.4.4 says Case 2 is not applicable to tension loads.
Note that in such a situation, you still need to be able to select Case 2, because you could have a dead, live and wind loads on the column where there are some uplift and some gravity load combinations. Since Case 2 provides a greater system effect than case 1, it is assumed that for tension, the member meets the requirements of Case 1 when Case 2 is selected to handle the compression load combinations.