Eigen analysis problem
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EricsonEncinaZ
- Posts: 108
- Joined: Mon Sep 16, 2013 1:14 pm
- Location: University of Auckland
Re: Eigen analysis problem
Are you sure that the same vecXZ vector passed in the geometrical transformation fits all the directions of the elements you defined?
You are saying tha all the elements are defined with the local z axis pointing in the global Y axis.
Also check units, mass and stiffnes definitions.
You are saying tha all the elements are defined with the local z axis pointing in the global Y axis.
Also check units, mass and stiffnes definitions.
Re: Eigen analysis problem
I opened it in GID just to see the geometry and then I defined elemets in GID and then created the tcl file from that just to chcek it if I done it correctly and it showed the same transformation for all elements. About the units the mass should be in kg/m or tons/m or kg/m^3 ? because I am not sure but the GID tcl shows tons.
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EricsonEncinaZ
- Posts: 108
- Joined: Mon Sep 16, 2013 1:14 pm
- Location: University of Auckland
Re: Eigen analysis problem
Mass in OpenSees should be given in units of force·time²/distance, like kN·s²/m. For example, if the base units of your model is kN and m and you want to define 1000kg then in order to be consistent with your base units you should define that mass as 1 kN·s²/m.
You can also create your own set of units, for example:
# Base units are kN and m
set kN 1.
set m 1.
set sec 1.
# Derived units
set N [expr $kN/1000.]
set mm [expr $m/1000.]
set MPa [expr $N/$mm**2]
set ton [expr $kN*$sec**2/$m]
set kg [expr $ton/1000.]
# Now you can define stuff using any of the defined units
set tw [expr 300*$mm]
set fc [expr 40*$MPa]
set M [expr 1000*$kg]
This way you can type your code using units. In the script examples on the OpenSees webpage there is a file called libUnits.tcl (or something like that) that has more units.
You can also create your own set of units, for example:
# Base units are kN and m
set kN 1.
set m 1.
set sec 1.
# Derived units
set N [expr $kN/1000.]
set mm [expr $m/1000.]
set MPa [expr $N/$mm**2]
set ton [expr $kN*$sec**2/$m]
set kg [expr $ton/1000.]
# Now you can define stuff using any of the defined units
set tw [expr 300*$mm]
set fc [expr 40*$MPa]
set M [expr 1000*$kg]
This way you can type your code using units. In the script examples on the OpenSees webpage there is a file called libUnits.tcl (or something like that) that has more units.
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emrecarter
- Posts: 2
- Joined: Tue Oct 06, 2015 6:23 am
- Location: University
Eigen analysis before and after transient analysis
Hi,
I modelled cantilever column by using fiber section. I obtained period of the structure with ''eigen'' command. Also, I obtained global stiffness matrix after static analysis with ''printA'' command. After that, I performed nonlinear dynamic analysis and obtained again period with ''eigen'' command. As expected, period increased. In order to obtained global stiffness matrix for damaged structure, I conducted static analysis and eigenvalue anlaysis one more time. However, I realized that periods are different for after nonlinear dynamic analysis and second static analysis (although there is no extra load at second static analysis). What can be reason this difference?
Note: Rayleigh damping for nonlinear dynamic analysis was created by using $alphaM and $betaKcomm coefficients.
I modelled cantilever column by using fiber section. I obtained period of the structure with ''eigen'' command. Also, I obtained global stiffness matrix after static analysis with ''printA'' command. After that, I performed nonlinear dynamic analysis and obtained again period with ''eigen'' command. As expected, period increased. In order to obtained global stiffness matrix for damaged structure, I conducted static analysis and eigenvalue anlaysis one more time. However, I realized that periods are different for after nonlinear dynamic analysis and second static analysis (although there is no extra load at second static analysis). What can be reason this difference?
Note: Rayleigh damping for nonlinear dynamic analysis was created by using $alphaM and $betaKcomm coefficients.