Cyclic Force Control loading

[ebaf65]

Hi,

I need to perform cyclic force control loading before cyclic displacement control loading.

The displacement control part is OK, but I don't know how should do force control part.

The forces I want to apply are a gravity load which is 100 KN and cyclic horizontal loading ( on the same node which gravity load is applied) which is [-10 10 -20 20 -30 30].

Can any one help me?

[fmk]

create 2 load patterns, in 1 place the gravity load, in the other the lateral loads. The time series for the first is constant, for the second it would be a path. In imposed displacements you specified the single point constraint in the second load pattern, for imposed force replace that with a nodal load.

[zfkrish]

I am trying to do something similar, but opposite. I have run a cyclic model using the displacement integrator first and would like to stop the analysis at the peak displacement and return the model to zero force (i.e. the residual displacement). The sequence that I have followed up to removing the load so far is:

1. define a load pattern using a nodal load for gravity and run the analysis under load control
2. define a load pattern for a unit lateral load at the top of column and run cyclic analysis under displacement control

At this point in the analysis everything has run smoothly, however I am not sure how to apply the next load sequence to "remove" the load. I have tried removing the second load pattern and applying a new load pattern with an equal and opposite value to the final force and then running load control, but that does not seem to work. Any suggestions?

[fmk]

if you want a sudden removal, remove the lateral load pattern .. if gradual, you need to issue a loadConst command and then add the final load pattern that will take it down to 0 over a number of steps .. w/o the loadConst the initial load keeps increasing.

[ebaf65]

fmk wrote:
> create 2 load patterns, in 1 place the gravity load, in the other the
> lateral loads. The time series for the first is constant, for the second it
> would be a path. In imposed displacements you specified the single point
> constraint in the second load pattern, for imposed force replace that with
> a nodal load.
Thanks very much.
I have not used path time series so far. As I mentioned, the force control loading contains a series of constant positive and negative forces.
However I couldn't understand your purpose from the following statement:

"... In imposed displacements you specified the single point constraint in the second load pattern, for imposed force replace that with a nodal load."
Could you please clarify it?
My other question: If I use the following script for path time series, what is the -dt? I don't know how should I define it.

timeSeries Path $tag -dt $dt -values {list_of_values} <-factor $cFactor> <-useLast> <-prependZero> <-startTime $tStart>