Which statement best describes the relation between strength and stiffness?

• A. A structure with higher strength can carry more load before failure, while higher stiffness means less deflection under the same load.
• B. They are interchangeable in design.
• C. Strength relates to load-bearing capacity; stiffness relates to deformation under load.
• D. Strength and stiffness are identical properties.

Answer: (C)

Strength and stiffness describe different aspects of how a member behaves under load. Strength is about how much load the member can carry before it fails or yields; stiffness is about how much it deflects or deforms under a given load. The statement that best captures their relationship says strength relates to load-bearing capacity, while stiffness relates to deformation under load. In design, you must consider both: a member can be very strong but not very stiff (it can bear high loads but may bend a lot under service loads), or very stiff but not very strong (it resists deflection but could fail if the stress becomes too high). The other options are incorrect because they either imply the properties are interchangeable, identical, or not distinct.