What does the term "dynamic load" refer to in structural engineering?

In structural engineering, "dynamic load" refers to loads that vary with time and can create significant changes in structural behavior. These loads can cause uncertainty in how structures respond because they may depend on various factors like frequency, amplitude, and loading duration. Dynamic loads include effects such as wind, earthquakes, traffic, and human activity, which introduce forces that can fluctuate significantly.

Understanding the nature of dynamic loads is essential for ensuring that structures can withstand these varying forces without failing. The ability to predict and analyze the impact of dynamic loads is critical for the safety and durability of structures.

The other definitions provided in the options do not appropriately describe a dynamic load. Instantaneous loads that cause immediate reactions describe a specific type of load but don’t encompass the broader and varied nature of dynamic loads. Permanent loads are static and do not change over time, which is in opposition to the concept of dynamic loading. Stress induced by thermal expansion pertains to changes in material properties and does not relate directly to load variation over time.