Should analysis time step be the same ground motion time ste

[Amirsardar13]

Hi,

Does anybody know:

Should the analysis time step be the same as ground motion time step, how much can it be smaller? Does OpenSees automatically break the ground motion into the "analysis time step"? Does OpenSees have the ability to define a variable "analysis time step"?

Thanks,

[vesna]

Ground motion time step and time increment for the analysis do not have to be the same. Yes, you can do variable transient analysis
http://opensees.berkeley.edu/wiki/index ... is_Command
http://opensees.berkeley.edu/wiki/index ... ze_Command

[Amirsardar13]

Thanks Vesna,
I am using Variable Transient Analysis. If I defined the analysis like below, does it change the time step to different values between the minimum and maximum values so that get the concergency? I don't think it does! What do I have to do if I would like to change the time step where there is no convergency?

$dt=0.02
analysis VariableTransient # define type of analysis: time-dependent
set ok [analyze 1 $dt 0.001 0.02 100]; # actually perform analysis; returns ok=0 if analysis was successful

[fmk]

if you want to see some variation, change the 100 at the end .. if you are converging in less than 100 iterations, it will quickly go to .02 and stay there .. the 100 is the number of iterations you would like convergence to occur in .. if a step takes less iterations it increases the time step .. if an iteration takes more it decreases the time step by a factor.