Why must abrupt changes in cross-sectional area be avoided in wood structures?

Abrupt changes in cross-sectional area in wood structures must be avoided primarily because they can cause stress concentrations. When the profile of a wooden element changes suddenly, it creates points where stress can accumulate much more than in surrounding areas. This concentration can lead to weaknesses, as these points are often where fractures or failures can initiate under load.

In structural design, maintaining a gradual transition in cross-section allows for a more uniform distribution of stress across the material, reducing the risk of structural failure. This is particularly important in aviation applications where the integrity of materials is critical for safety and performance.

While the other aspects mentioned, such as weight distribution and moisture accumulation, are relevant to overall design considerations, they are secondary to the primary concern of stress concentration which directly impacts the mechanical performance and safety of wooden structures in aviation.