The use of lumber for formwork and falsework must be in accordance with the standard CSA O86 – Engineering design in wood. The Canadian Wood Council (CWC) Wood Design Manual should be used as a reference guide. (CSA S269.1 Clause 6.8.1)<\/p>\n\n\n\n
The CSA S269.1, Clause 6.8.3, specifies the following modification factors for wood elements use for formwork and falsework.<\/p>\n\n\n\n Further more, the CSA O86 specifies the following modification factors, depending on the assembly of the panel and the sizes of the lumbers.<\/p>\n\n\n\n For joisted panels and stud wall Size factor for visually graded lumber<\/p>\n\n\n\n Bearing – Compression perpendicular to grain, \\(K_{Zcp}\\) Axial – Compression parallel to grain, \\(K_{Zc}\\) Treated wood<\/p>\n\n\n\nService condition: Normal service condition is dry.<\/td> \\(K_S=1\\)<\/td><\/tr> Load duration factor: For columns, normal duration.
For all other member and connection, short duration.<\/td>\\(K_D=1\\)
\\(K_D=1.15\\)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
CSA O86, clause 6.4.4, System factor, \\(K_H\\), for visually graded lumber<\/strong><\/p>\n\n\n\nCase 1:
Applies to bending, shear and axial properties if the system consist of more than three parallel members spaced 610mm apart maximum. For example, 4×6 joists supporting a concrete slab sheathed with a lightly nailed plywood.<\/td>\\(K_H=1.1\\)<\/td><\/tr> Case 2:
Applies to bending and shear properties if the sheathing of the system described by case 1 is nailed to the joists with 2in long nails min, spaced 150mm max along the edge of the sheathing panels and spaced 300mm in the field of the panels. <\/td>\\(K_H=1.4\\)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n Lumber<\/td> \\(K_{Zb}\\) and \\(K_{Zv}\\)<\/td><\/tr> 2×4<\/td> 1.7<\/td><\/tr> 2×6<\/td> 1.4<\/td><\/tr> 2×8<\/td> 1.2<\/td><\/tr> 2×10<\/td> 1.1<\/td><\/tr> 2×12<\/td> 1.0<\/td><\/tr> 4×4<\/td> 1.7<\/td><\/tr> 4×6<\/td> 1.5<\/td><\/tr> 4×8<\/td> 1.3<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
From CSA O86, Clause 6.5.6.4
For width over depth ratio equal or less than 1 \\(K_{Zcp}=1.00\\)
For width over depth ratio equal or more than 2 \\(K_{Zcp}=1.15\\)
Interpolation is allowed for intermediate ratios<\/p>\n\n\n\nOrientation<\/td> Lumber<\/td> Nominal \\(\\frac wd\\)<\/td> Actual \\(\\frac wd\\)<\/td> \\(K_{Zcp}\\)<\/td><\/tr> On edge<\/td> 2×4<\/td> 2.0<\/td> 2.3<\/td> 1.15<\/td><\/tr> On edge<\/td> 2×6<\/td> 3.0<\/td> 3.7<\/td> 1.15<\/td><\/tr> On edge<\/td> 2×8<\/td> 4.0<\/td> 4.8<\/td> 1.15<\/td><\/tr> On edge<\/td> 2×10<\/td> 5.0<\/td> 6.2<\/td> 1.15<\/td><\/tr> On edge<\/td> 2×12<\/td> 6.0<\/td> 7.5<\/td> 1.15<\/td><\/tr> On edge<\/td> 4×4<\/td> 1.0<\/td> 1.0<\/td> 1.00<\/td><\/tr> On edge<\/td> 4×6<\/td> 1.5<\/td> 1.6<\/td> 1.075<\/td><\/tr> On edge<\/td> 4×8<\/td> 2.0<\/td> 2.1<\/td> 1.15<\/td><\/tr> Flat<\/td> 1×6<\/td> 0.2<\/td> 0.1<\/td> 1.00<\/td><\/tr> Flat<\/td> 2×4<\/td> 0.5<\/td> 0.4<\/td> 1.00<\/td><\/tr> Flat<\/td> 2×6<\/td> 0.3<\/td> 0.3<\/td> 1.00<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Clause 6.5.5.2.4<\/p>\n\n\n\n