Which structural element is primarily subjected to flexure?

The structural element that is primarily subjected to flexure is the beam. Beams are designed to carry loads that create bending moments, which induce flexural stresses within the material. When a load is applied to a beam, it bends, causing one side of the beam to experience compression while the other side undergoes tension. This bending action is a direct result of the beam's function in transferring loads horizontally between supports.

In contrast, columns are more significantly subjected to axial loads and shear forces, as they primarily carry vertical loads from beams and slabs above them down to the foundations. Foundations serve to distribute the loads from the structure to the ground, experiencing different types of stresses such as bearing and shear rather than flexural stresses. Slabs can experience some bending due to load conditions, but they are typically treated as flat structural elements that are primarily supported on their edges and subjected to both bending and shear.

Therefore, the primary role of beams in resisting bending moments and enabling the structure to maintain its integrity under such conditions underscores why beams are the correct answer regarding structural components that are primarily subjected to flexure.