Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

50 Chapter Four
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d/b Range
Lateral Constraints for Bending Stability
d/b ≤ 2 No lateral support is required; includes 2 × 4, 3 × 4,
4 × 6, 4 × 8, and any members used flat, examples
are 4 × 2, 6 × 2, 8 × 2
2 < d/b ≤ 4 Ends shall be held in position, as by full depth solid
blocking, bridging, hangers, nailing, bolting, or other
acceptable means; examples are 2 × 6, 2 × 8, 3 × 8
4 < d/b ≤ 5 Compression edge of the member shall be held
in line for its entire length to prevent lateral
displacement and ends of member at point of
bearing shall be held in position to prevent rotation
and/or lateral displacement; such as a 2 × 10.
5 < d/b ≤ 6 Bridging, full depth solid blocking, or diagonal crossbracing
must be installed at intervals not to exceed
8 ft, compression edge must be held in line for its
entire length, and ends shall be held in position
to prevent rotation and/or lateral displacement;
example is a 2 × 12
6 < d/b ≤ 7 Both edges of the member shall be held in line
for its entire length and ends at points of bearing
shall be held in position to prevent rotation and/or
lateral displacement; examples are deep and narrow
rectangular members
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Note: d and b are nominal dimensions.
TABLE 4-6 Lateral Constraints for Stability of Bending Members
Adjustment Factor for Bending Stress, F b
Thickness (breadth)
Width (depth) 2-in. and 3-in. 4-in.
2-in. 1.0 –
3-in. 1.0 –
4-in. 1.1 1.0
5-in. 1.1 1.05
6-in. 1.15 1.05
8-in. 1.15 1.05
10-in. and wider 1.2 1.1
TABLE 4-7 Adjustment Factors C fu
for Flat Use
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