Which statement best defines dynamic loads?

• A. Result from impacts (ie. snow, bridge, elevator) (change rapidly)
• B. Loads that never move or change
• C. Loads caused only by gravity
• D. Loads due to temperature changes

Answer: (A)

Dynamic loads are forces that vary with time, often changing rapidly, so the structure must respond to varying conditions rather than a single constant load. This includes forces from impacts and moving or accelerating actions, like a vehicle crossing a bridge or the start and stop of an elevator. Because the magnitude and distribution of these loads change quickly, engineers analyze them with dynamic considerations to account for inertia and potential amplification of effects.

Static loads stay constant or change very slowly, such as gravity-induced dead loads, while loads caused by temperature changes develop gradually and are not impulsive. So a statement that emphasizes impacts and rapid changes best captures what dynamic loads are.