TABLE OF CONTENTS In this beam example and those that follow, the span lengths for bending and shear are, for simplicity, taken to be the same length. However, the designer may choose to determine the design moment based on the clear span plus one-half the required bearing length at each end (Sec. 6.2) and the design shear at a distance d from the support (Sec. 6.5). These different span length considerations are described in Example 6.13 (Sec. 6.5) for a simply supported beam.
In Example 6.18 a typical sawn lumber beam is designed for a roof that is essentially flat. Minimum slope is provided to prevent ponding. An initial trial beam size is determined from bending stress calculations. The extensive list of possible adjustment factors for bending stress is reduced to seven for the case for a visually graded sawn lumber beam with bending about the strong axis (see Example 6.10 in Sec. 6.4).
The beam in this problem is used in dry-service conditions and at normal temperatures, and C M and C t both default to unity. In addition, the roof sheathing provides continuous lateral support to the compression side of the beam. Consequently, there is no reduction in moment capacity due to lateral stability, and C L is unity. The beam is not incised for pressure treatment since it is protected from exposure to moisture in service. Accordingly, C i also defaults to unity. Therefore, the potential number of...
