Which of the following is NOT considered a structural element?

Plastic is not considered a structural element primarily because it lacks the strength and durability that materials like wood, concrete, and steel provide for load-bearing applications. Structural elements are typically categorized based on their ability to support loads and withstand various stresses in construction. Wood, concrete, and steel are all traditional materials that are specifically chosen for their high tensile and compressive strengths, making them suitable for constructing frameworks, foundations, and other essential parts of a building.

While plastic can be used in construction, it is generally utilized for non-structural components such as insulation, finishing, or to create fixtures and fittings. Its properties do not meet the necessary criteria to consider it a primary material for structures that require significant load bearing or resistance to environmental factors. Therefore, it is correctly identified as the choice that does not belong in the category of structural elements.