Which of the following statements is true regarding positive bending moments?

The correct answer highlights that positive bending moments create compression in the upper fibers of a beam. When a beam is subjected to a positive bending moment, it tends to bend downwards. This results in the upper portion of the beam being pushed together, which generates compressive stresses in the upper fibers. Concurrently, the lower portion of the beam experiences tensile stresses as it stretches. Understanding this behavior is essential for structural analysis and design, as it influences how materials are selected and how beams are sized to ensure they can appropriately handle the forces applied to them.

The other statements do not accurately describe the behavior associated with positive bending moments. While a bending moment may be related to shear forces in some contexts, it does not suggest they specifically occur at points of maximum shear. Rather, a bending moment can be analyzed independently of shear forces. Similarly, flat curvature is not characteristic of beams under positive bending moments; instead, beams will exhibit a curvature that is concave up when positive moments are applied. Thus, the focus on the compressive stresses in the upper fibers helps clarify the behavior of beams under positive bending moments in structural engineering contexts.