# 3.1.11.2. Uniform Excitation¶

The UniformExcitation pattern allows the user to apply a uniform excitation to a model acting in a certain direction. The command is as follows:

pattern UniformExcitation $patternTag$dof -accel $tsTag <-vel0$vel0> <-fact $cFact> Argument Type Description$patternTag

integer

$dof integer dof direction the ground motion acts$tsTag

integer

tag of the TimeSeries series defining the acceleration history.

$vel0 float the initial velocity (optional: default=0.0)$cFact

float

constant factor (optional: default=1.0)

Warning

The responses obtained from the nodes for this type of excitation are RELATIVE values, and not the absolute values obtained from a multiSupportPattern. This is a consequence of the equation of motion being solved:

$M\ddot{U} + C\dot{U} + K U = P(t)$

$P(t) = -c_{Fact} M l \ddot{u_g}$

where $$l$$’ is a vector of 1’s and 0’s, with a 1 corresponding to all matrix equations in the $dof degree-of-freedom direction and 0 for all other degrees-of-freedom. The $$\ddot u_g$$ is obtained from the time series. Example: The following example shows how to construct a UniformExcitation pattern with a tag of 2 acting in the 1 direction. The acceleration for the pattern comes from the Path TimeSeries with tag 3 which has been created using the contents of the elCentro.dat file, a $$\delta t = 0.02$$, and a scale factor given by the variable g, which has been set to 386.1. 1. Tcl Code set g 386.1 timeSeries Path 3 -filePath elCentro.dat -dt 0.02 -factor$g
pattern UniformExcitation  2 1 -accel 3

1. Python Code

g = 386.1
timeSeries('Path', 3, '-dt', 0.005, '-filePath', 'A10000.dat', '-factor', g)
pattern('UniformExcitation', 2, 1, '-accel', 3)


Code Developed by: fmk