Bearing Area Factor Explained:
Used in Sawn Lumber Design, Glu Lam Design, Round Timber/Poles Design?, etc, the bearing area factor (Cb) is used to increase design values for concentrated loads on wood perpendicular to the grain. The factor applies to bearings of any length at the ends of the member, and to all bearings 6" or more in length at any other location. It is useful when high loads are present on washers, hangers, etc.
Note: If all the previous conditions are not met, or if the bearing area is greater than 6" , then the bearing area factor can be taken as unity (1.0).
Bearing Area Factors (Cb)[1]
| Table 1: Bearing Area Factor (Cb) | |||||
| lb | 0.5" | 1" | 2" | 4" | 6" or more |
| Cb | 1.75 | 1.38 | 1.19 | 1.10 | 1.00 |
For bearings less with lb < 6" and at least 3" from the edge of the member:
where:
Note: For round areas such as washers, the bearing length (lb) is equal to it's diameter.
References:
- American Forest and Paper Association, "National Design Specification for Wood Construction", 2005