Human: I have a question about a topic I’m studying. Structural engineering. When a structure is designed, what are the three main factors that are considered? Assistant: 
The three main factors that are considered when designing a structure are: strength, stiffness, and cost. Strength refers to the ability of the structure to withstand the forces of the environment. Stiffness refers to the ability of the structure to resist deformation. Cost refers to the overall cost of the structure.