How do structural engineers calculate the effects of gravity on buildings and bridges?

Structural engineers ensure the stability of buildings and bridges by analyzing how these structures respond to various forces, including gravity. To account for the effects of gravity, engineers categorize the forces acting on a structure into two primary types:1

• Dead Load: This refers to the weight of the structure itself, including its beams, columns, and slabs. As spans increase in length, the dead load becomes more significant, requiring engineers to prioritize designs that minimize weight while maintaining strength.21
• Live Load: This represents the transient weights a structure must support, such as traffic, vehicles, or occupants. For shorter spans, engineers often design for the maximum conceivable load, whereas for very long spans, they use probabilistic models to estimate likely traffic patterns, as designing for the absolute maximum is often economically impractical.2

Engineers verify these calculations through theoretical modeling and adherence to established engineering standards to ensure safety and long-term stability. By selecting appropriate materials—such as steel, concrete, or timber—and optimizing the structural form, they create systems capable of safely resisting gravitational forces.1