Hi all,
Can anyone explain me how to perform eigen analysis of a 3D frame?
I had done the eigen analysis of 2D frame and it had run successfully.
Mainly I need to find out mass participation factor from the obtained eigen vectors. Am not understanding how to obtain correct eigen vectors?
Can anyone please help me?
Thanks in advance
Eigen analysis of a 3D RC frame?
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venkateshyadav
- Posts: 52
- Joined: Fri Mar 17, 2017 11:01 am
- Location: IIT Patna
Re: Eigen analysis of a 3D RC frame?
it is exactly same as 2d!
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venkateshyadav
- Posts: 52
- Joined: Fri Mar 17, 2017 11:01 am
- Location: IIT Patna
Re: Eigen analysis of a 3D RC frame?
fmk wrote:
> it is exactly same as 2d!
Yes , the entire code is same as 2d. But main problem, how to get time periods in a specified direction. I need time period in x and z direction. And also the eigen vectors am not obtaining correctly. I will briefly describe my code here.
Am assigning rigid diaphragm and the nodes are 1121 , 1122 and 1123.
Assigning mass to the 1 and 3 degree of freedom as per general notation i.e., translational x and z directions. For example : mass 2 [expr 0.017*$m1] 0. [expr 0.017*$m1] 0. 0. 0.
Number of modes as 3 since I need only transnational eigen vectors and it is 3 story frame.
Code as follows which is just modified form of 2D:
set NStory 3; # number of stories above ground level
for { set k 1 } { $k <= $numModes } { incr k } {
recorder Node -file [format "modes/mode%i.out" $k] -node 1121 1122 1123 -dof 1 "eigen $k"
}
I got the doubt in results when finding the sum of modal mass coefficient as per ATC 40 considering the obtained eigen results of one direction is not equal to 1 or 100%.
But I obtained correct results with 2d frame. I guess there is some problem in my code.
Can you please suggest any help regarding it.
Thanks
> it is exactly same as 2d!
Yes , the entire code is same as 2d. But main problem, how to get time periods in a specified direction. I need time period in x and z direction. And also the eigen vectors am not obtaining correctly. I will briefly describe my code here.
Am assigning rigid diaphragm and the nodes are 1121 , 1122 and 1123.
Assigning mass to the 1 and 3 degree of freedom as per general notation i.e., translational x and z directions. For example : mass 2 [expr 0.017*$m1] 0. [expr 0.017*$m1] 0. 0. 0.
Number of modes as 3 since I need only transnational eigen vectors and it is 3 story frame.
Code as follows which is just modified form of 2D:
set NStory 3; # number of stories above ground level
for { set k 1 } { $k <= $numModes } { incr k } {
recorder Node -file [format "modes/mode%i.out" $k] -node 1121 1122 1123 -dof 1 "eigen $k"
}
I got the doubt in results when finding the sum of modal mass coefficient as per ATC 40 considering the obtained eigen results of one direction is not equal to 1 or 100%.
But I obtained correct results with 2d frame. I guess there is some problem in my code.
Can you please suggest any help regarding it.
Thanks
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selimgunay
- Posts: 916
- Joined: Mon Sep 09, 2013 8:50 pm
- Location: University of California, Berkeley
Re: Eigen analysis of a 3D RC frame?
For the 3D case where there is coupling between translation and rotation of the rigid diaphgram, you can not just use the translation components of the eigenvectors for computation of modal mass, you also need rotations. Please see "multistory buildings with unsymmetric plan" section of the Dynamics of Structures book by Anil Chopra.