Structural dynamics

Structural dynamics is a branch of structural analysis which covers the behavior of a structure subjected to dynamic loading. Dynamic loading is any time-varying loading which changes quickly enough that the response of the structure differs from the response to the same loading applied statically. Causes of dynamic loading include people, wind, waves, traffic, earthquakes, and blasts. Dynamic analysis can be used to find dynamic displacements, time history, and natural frequencies and mode shapes.

Whether a given load should be treated as static or dynamic depends on how quickly the load varies in comparison to the structure's natural frequency. If it changes slowly, the structure's response may be determined with static analysis, but if it varies quickly (relative to the structure's ability to respond), the response must be determined with a dynamic analysis.

Dynamic analysis for simple structures can be carried out analytically, but for complex structures finite element analysis is more often used to calculate the mode shapes and frequencies.

Structural analysis is mainly concerned with finding out the behavior of a physical structure when subjected to force. This action can be in the form of load due to the weight of things such as people, furniture, wind, snow, etc. or some other kind of excitation such as an earthquake, shaking of the ground due to a blast nearby, etc. All loads are dynamic in the literal sense, because at some point in time they were not present. The distinction is made between the dynamic and the static analysis on the basis of whether the applied action has enough acceleration in comparison to the structure's natural frequency. If a load is applied sufficiently slowly, the inertia forces (Newton's first law of motion) can be ignored and the analysis can be simplified as static analysis.