8. Calculating the natural period of a construction's vibration mode

Knowledge of a structure's natural period is necessary to determine the dynamic amplification coefficients in the wind direction and in the perpendicular direction. It may therefore be necessary to calculate this period in several directions, depending on the configuration of the building.

The value of the period is directly linked to that of the excited mass. Therefore, if wind action is to be combined with snow action, the period must, as a matter of principle, be evaluated using the mass corresponding to the building's own weight plus the half-snow.

The main methods used to calculate periods are described below.

• Modal analysis

  Structural calculation software is now widely used. These programs are now equipped with "dynamic modules", making it easy to carry out modal...