I've a model in which I imposed the displacements to the ground (in order to simplify, in this sample I used the same TH):
From:
https://opensees.github.io/OpenSeesDocu ... ttern.html
I read:
The TCL code I have:The results for the responses at the nodes are the ABSOLUTE values, and not relative values as in the case of a UniformExcitation.
When using MultiSupport pattern, the ground motions are applied by specifying for each constrained node a ground motion. This is done using the Imposed Motion Command command. The ground motions at each of the supports is specified using a Ground Motion. When enforcing the constraint at the node, the imposedMotion constraint will obtain the displacement from the ground motion. If the groundMotion was built by user specifying the acceleration, the trapezoidal rule is used for integration to obtain the displacements.
Code: Select all
timeSeries Path 100 -time { 0 0.005 0.01 0.015 } -values {0 1.55 6.25 1.37 }
pattern MultipleSupport 100 {
groundMotion 1 Plain -disp 100 -fact 1
imposedSupportMotion 1 1 1
imposedSupportMotion 3 1 1
}
From recorders, I obtain ZERO ground velocity and acceleration in constrained nodes (e.g. 1 and 3). I'd expect at least velocity to be different than 0.
This is a problem because I'm using a dashpot modelled with the so called "sky-hook" tecnique, in which one node of the dashpot is constrained to the ground. Since velocity in internal node is ABSOLUTE, the force given by dashpot is different from the same dynamic analysis conducted with UniformExcitation pattern (see also https://portwooddigital.com/2021/08/29/ ... xcitation/).
Which is the reasons why in MultipleSupport pattern we have zero velocity and acceleration on grounded nodes?
By imposing a piece-wise displacement time-history, I expect velocity to be non-zero, while acceleration, as a second derivative over time, is expected to be numerically zero.