Final answer:
Mixed oak timbers are known for their complex structure and may have better bending strength than Douglas fir, but empirical data is required for a definitive comparison. Oak wood's large rays and variation in vessel size contribute to its strength properties.
Step-by-step explanation:
The bending strength, or modulus of rupture, is an important property in timber used for structural purposes. It defines how much stress a material can withstand before failure in bending. Mixed oak timbers are known to have a complex structure, as evidenced by properties such as the presence of large diameter vessels and the production of vessel-free wood late in the spring, as well as large rays composed of parenchyma cells. The red oak, which is a type of oak wood, is known for having a prominent growth ring pattern due to these features.
Comparatively, Douglas fir is also a strong wood, but the structure of oak, which includes these large rays and variation in vessel size, contributes to its overall strength and stiffness. This suggests that, structurally, the oak might have better resistance to bending stresses.
In general, oak is typically known for its durability and strength which includes properties like bending strength. However, to directly answer the question about whether mixed oak timbers have a greater bending strength per square inch than Douglas fir, it would require specific empirical data comparing the two. Therefore, without the precise data, one cannot conclusively say that one has greater bending strength than the other. Nonetheless, it is commonly accepted that different species of oak, including red oak, tend to have high bending strength. So, the assertion might still be plausible even if it's not explicitly confirmed by the provided information.