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>






unique tag among load patterns



dof direction the ground motion acts



tag of the TimeSeries series defining the acceleration history.



the initial velocity (optional: default=0.0)



constant factor (optional: default=1.0)


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:

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

and how the loads are applied with this load pattern.

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

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.


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