How can period in nonlinear dynamic analysis?

[afsaneh]

Haw i can calculate moment to moment period in nonlinear dynamic analysis?
Thank you very much for your help.

[vesna]

You have to do the analysis in a loop (step by step) and to insert eigen command in there. I posted an example for this in one of the posts on a message board.

[afsaneh]

sorry,i could not find the example,please send me the link of it.
tnx alot for your help.

[vesna]

Here is the link:
http://opensees.berkeley.edu/community/ ... =2&t=23174

[afsaneh]

tnx alot for your help

[afsaneh]

hello,I calculated time history of natural's period of structre in nonlinear dynamic analysis,I want to know how the software do this and calculate stiffness redusing?
tnx for your help

[vesna]

What is your question again?

[afsaneh]

hello,I calculated moment to moment period of structre in nonlinear dynamic analysis with following statements:
################ create the Transient analysis###################
set period "PeriodS.txt"
set Periods [open $period "w"]
set pi 3.141593

set deltaT 0.02
set NumTransiant 1151
set tFinal [expr $NumTransiant*$deltaT]


loadConst -time 0.0

wipeAnalysis
constraints Transformation
numberer RCM
system UmfPack
test NormDispIncr 1.0e-8 100
algorithm Newton
integrator Newmark 0.5 0.25
analysis Transient

set currentTime 0.0
while {$currentTime < $tFinal} {
set ok [analyze 1 $deltaT]

set lambda [eigen 1]


set T {};
foreach lam $lambda {
lappend T [expr (2*$pi)/sqrt($lam)]
}
foreach t $T {
puts $Periods " $t"
}

set currentTime [getTime]
}


close $Periods

//*********
i want to know software procedure in this calculation and how it uses stiffness reducing?

[vesna]

After each step of the analysis the eigen analysis is performed using the current stiffness of the system.

[afsaneh]

hello,thanks for your help,but i want to know the explanation of the theory that software uses for calculate stiffness redusing in each step

[vesna]

OpenSees is open source which means that by looking at the source code you can see the theory of each class.
The link to source code is: http://opensees.berkeley.edu/WebSVN/lis ... runk%2FSRC

[afsaneh]

tnx alot

[talebian.s.e]

Dear Vesna,

How can I calculate the moment to moment period in a pushover analysis? I tried the procedure mentioned above but I could not obtain the periods.

The following is my pushover algorithm:

set Fj5 [expr 5000*$N];
set Fj4 [expr 4000*$N];
set Fj3 [expr 3000*$N];
set Fj2 [expr 2000*$N];
set Fj1 [expr 1000*$N];

set Dmax [expr 0.05*$LBuilding ]; # maximum displacement of pushover. push to 10% drift.
set Dincr [expr 0.001*$LBuilding ]; # displacement increment. you want this to be small, but not too small to slow analysis

# -- STATIC PUSHOVER/CYCLIC ANALYSIS
# create load pattern for lateral pushover load coefficient when using linear load pattern


pattern Plain 200 Linear { # define load pattern
load 5 $Fj1 0 0
load 9 $Fj2 0 0
load 13 $Fj3 0 0
load 17 $Fj4 0 0
load 21 $Fj5 0 0

}; # end load pattern

# ----------- set up analysis parameters
set Tol 1.0e-4; # convergence tolerance for test
constraints Transformation; # how it handles boundary conditions
numberer RCM; # renumber dof's to minimize band-width (optimization), if you want to
system BandGeneral ; # how to store and solve the system of equations in the analysis (large model: try UmfPack)
test NormDispIncr $Tol 20 ; # determine if convergence has been achieved at the end of an iteration step
algorithm Newton ; # use Newton's solution algorithm: updates tangent stiffness at every iteration
integrator DisplacementControl $IDctrlNode $IDctrlDOF $Dincr;
analysis Static
# --------------------------------- perform Static Pushover Analysis
set Nsteps [expr int($Dmax/$Dincr)]; # number of pushover analysis steps
set ok [analyze $Nsteps]; # this will return zero if no convergence problems were encountered
set fmt1 "%s Pushover analysis: CtrlNode %.3i, dof %.1i, Disp=%.4f %s"; # format for screen/file output of DONE/PROBLEM analysis
if {$ok != 0} {
# if analysis fails, we try some other stuff, performance is slower inside this loop
set Dstep 0.0;
set ok 0
while {$Dstep <= 1.0 && $ok == 0} {
set controlDisp [nodeDisp $IDctrlNode $IDctrlDOF ]
set Dstep [expr $controlDisp/$Dmax]
set ok [analyze 1 ]
# if analysis fails, we try some other stuff
# performance is slower inside this loop global maxNumIterStatic; # max no. of iterations performed before "failure to converge" is ret'd
if {$ok != 0} {
puts "Trying Newton with Initial Tangent .."
test NormDispIncr $Tol 2000 0
algorithm Newton -initial
set ok [analyze 1]
test NormDispIncr $Tol 500 0
algorithm Newton
}
if {$ok != 0} {
puts "Trying Broyden .."
algorithm Broyden 8
set ok [analyze 1 ]
algorithm Newton
}
if {$ok != 0} {
puts "Trying NewtonWithLineSearch .."
algorithm NewtonLineSearch 0.8
set ok [analyze 1]
algorithm Newton
}

}; # end while loop
}; # end if ok !0

# -----------------------------------------------------------------------------------------------------
if {$ok != 0 } {
puts [format $fmt1 "PROBLEM" $IDctrlNode $IDctrlDOF [nodeDisp $IDctrlNode $IDctrlDOF] "milimeter"]
} else {
puts [format $fmt1 "DONE" $IDctrlNode $IDctrlDOF [nodeDisp $IDctrlNode $IDctrlDOF] "milimeter" ]
}

[mhscott]

Did you define any mass? Even though it's static pushover, the eigenvalue solver still needs a mass matrix.

[talebian.s.e]

Dear Michael,
Thanks for kind consideration. Yes, I have defined nodal mass. I just want to know how to calculate the step to step period during pushover analysis.