Multi Nodal time-step displacement

[PreciseLogic]

STKO Team,

Please help. I am having an extremely difficult time finding an answer to this question. I have a multi-nodal column (14 nodes) that each have a time history displacement record (derived from a SAP2000 analysis for the overall building). I need to push my column over so that at each time step, each of the 14 nodes matches the prescribed displacement for that time step.

I have created a Time Series Path for each node, and manually inputted the displacements for each, but at the "Conditions" menu all I can find is Model / Loads / sp, and once at sp it appears that I cannot link to my list in the Time Series Path, nor do anything other than input a single displacement?

Please advise how to do what I need to do for this push-over analysis?

Thank you!!

[STKO Team]

In condition, you create the reference imposed displacement (sp). Call it Ref_Load.
Then, in the analysis step, you create a load pattern with the Path-time-series (which defined the load-multiplier Lambda as a function of time) you want and put that sp in the load pattern.
In OpenSees, at each time step, the imposed sp will be: Ref_Load * Lambda(current_time)

[PreciseLogic]

STKO Team

Thank you for the reply. I am a little confused. The nodal displacements come from a time-history analysis of seismic motion. This would be a classic time-history analysis, except that instead of a unique ground acceleration at each of 8000 steps, we have unique nodal displacements at each step. (See attached png file). So, using a multiplier like Lambda, I would need 14 different Lambdas (one for each displaced node), but also the Lambdas would change for each step...

Nodal Disp.png (31.86 KiB) Viewed 2668 times

Isn't there a way to load in a list of displacmenets for each node at each step? Or, if I am completely misunderstanding your response, could you please possibly include an example file for me to model from?

Thank you again,

[PreciseLogic]

STKO team,

Can you please take another look at this issue? I am still without a solution for my forced-displacement time-step problem.

Thank you so much.

[STKO Team]

You need to understand how opensees works with loads/sp:
Imagine the case in which Node01 is subjected to the following time-displacement pattern:
t=[0.0, 0.5, 1.0], u=[0.0, 10.0, 0.0] (a triangular pattern with peak displacement = 10.0 units)

• Define a Defintions->timeSeries->PathSeries with the previously mentioned vectors (times, and loadMultipliers)
• In condition you define the reference SP for Node01 (set it to 1.0, because the loadMultipliers already contain the actual values for displacements)
• In AnalysisSteps->loadPattern-> add the condition (sp) and the timeSeries

Repeat for all nodes.

Alternatively you can use Tcl scripting to make it more automatic, like programmatically load those values from text files.
But it required programming capabilities