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The drainage system is modelled as perfect drains; fixed pore pressure conditions are applied to them throughout the analysis. A pore pressure condition can be specified using the Timeseries command (to specify the behaviour of the condition vs. Time) and the MultipleSupport groundmotion command to specify the node and DOF to which the Timeseries applies at.
The code below is used to specify the pore pressure at a point on the top of the EQ-drain:
set Timeseries64 "Constant -factor 0.4495"
pattern MultipleSupport 3 {
...
groundMotion 64 Plain -vel $Timeseries64
imposedMotion 64 3 64
...
}
The command creates a MultipleSupport pattern object with id 3, an object that allows users to define a fixed acceleration, velocity, or displacement of a specific DOF on a specific node. It then applies the conditions for every node. For every node we specify a imposedMotion object that attaches a specified groundMotion to the node. In this case, we create a groundMotion object with id 64 that is Plain, of type velocity, and has as arguments the value of the parameter Timeseries64 (Constant timeseries of value 0.4495). By means, of this set of commands we specify that the pore pressure in node 64 has a value of 0.4495. If applying this boundary condition does not work, one should specify acceleration, velocity, and displacement boundary conditions all at the same time, at the same node.