How to get the natural frequency of damaged structure?

[Sangwook]

Hello, everyone

I'm trying to get the natural frequency of the building before and after earthquake.
When I obtain the natural frequency from initial state of the building, I usually put the eigen command between "nodal mass" of the building and "recorders"

But, I want to get the natural frequency of the damaged building.
In this case, I wonder if I should insert the eigen command twice in the script.

The topic from "http://opensees.berkeley.edu/community/ ... =2&t=48016" is similar to my question.


Thanks & Regards

[fmk]

you can insert the eigen command as mny times as you like in the scipt .. it calculates based on current K and M

[Sangwook]

Thank you for your help.

However, domain error was occurred as below.
Is there any solution for this problem?

---------------------------------------------------------
domain error: argument not in valid range
while executing
"expr sqrt($lam)"
("foreach" body line 2)
invoked from within
"foreach lam $lambda {
lappend omega [expr sqrt($lam)]
lappend f [expr sqrt($lam)/(2*$pi)]
lappend T [expr (2*$pi)/sqrt($lam)]
}"
("for" body line 10)
invoked from within
"for {set i 1} {$i < $NumSteps} {incr i 1} {
analyze 10 $dt
# perform eigen analysis
#-----------------------------
set lambda [eigen 1];
set omega {}
..."
(file "IMKmodel.tcl" line 264)
---------------------------------------------------

[fmk]

the problem is that the eigenvalues probably came back NEGATIVE .. before you do a sqrt() check i is indeed positive