The Uniform Base Excitation PropertyManager applies uniform excitations to all locations that are restrained in the specified directions for linear and nonlinear dynamic studies.
The excitations you can apply depend on the type of the study:
- For modal time history studies, you can define displacement, velocity, or acceleration uniform base excitations as functions of time.
- For harmonic studies, you can define displacement, velocity, or acceleration uniform base excitations as functions of frequency.
- For random vibration studies, you can define displacement, velocity, or acceleration uniform base excitations in the global directions as functions of frequency.
- For response spectrum analysis studies, you can define uniform base excitation in terms of a given displacement, velocity, or acceleration response spectrum.
The response spectrum contains the peak responses over time for a range of single-degree-of-freedom (SDOF) systems subjected to a particular base motion as a function of their natural frequency or vibration period. Each response spectrum curve corresponds to a particular modal damping ratio.
In a response spectrum analysis study, you can apply multiple response spectra definitions for uniform or selected base excitations. In case of multiple response spectra definitions, the total response is calculated by the square root of the sum of the squares of the individual responses.
- For nonlinear dynamic studies, you can apply acceleration uniform base excitations in the global directions as functions of time.
You cannot define uniform base excitation in a cylindrical or spherical coordinate system.
When you define a uniform base excitation, you can request the evaluation of relative or absolute displacements and velocities. Relative response quantities are relative to the base response. Nonlinear dynamic studies always evaluate relative displacements and velocities.
For accelerations, only absolute values are evaluated.