Eigen value Analysis problem in the real structure 1

[Zouatine]

Dear all,

I'm designing 4 stories building steel structure on Etabs Software as you can see in the next Figure, however, I'm looking for the vectors of the first two-mode shapes of the structure in order to use them in one method that I'm using. the problem is when I look at the result I am not able to find the mode shapes vector value, it just gives the behavior of the first two modes without values. I designed the same structure in SAP2000 but the issue wasn't solved.

I'm really stuck with this part, could you please suggest me a solution for it.

thank you for your help in advance.

 

[engineering_patrol]

Can you see the deformation values of the Modal case? They represent the vector you are looking for.

 

[Blackstar123]

By default, modal results are not included in the ETABS tabular results. If you want to see the modal results in table, you need to first modify the Table option as shown.

Alternatively,

Once you've modified the view options, you can get the modal shapes through "diaphragm center of mass displacement" option.

 

[Zouatine]

Dear Mr. Blackstar123 ,

thank you for your reply,

After reading your comment which I do appreciate, I applied exactly the same as you mentioned and I got the result of the displacement of each diaphragm, the remaining thing is I got a little bit confused after reading your comment and I hope that you will correct me, sir, does the Eigenvector the one we get from the formula (k-omega^2).v=0 means the displacement if I'm not mistaken it is not, however in order to check I did the hand calculation of three stories frame structure and I checked the values of the time period and I got the same but when I compare the value from the table of diaphragm center of mass displacement after normalizing them, it does not give the same result.

could you please correct me,

this is the eigenvector from Matlab,

and this is the work from Etabs

and after normalizing them I got M1=(0.733 0.594 0.3308 ) M2= (-0.619 0.28776 0.7309) M3=( -0.3687 0.7325 -0.572)

I'm waiting for your reply , thank you for help

 

[Blackstar123]

The values that are viewed with the diaphragm displacement option are the total ones. Since, the shape is what matters the most for modal cases, the magnitude usually has no meaning.
But if you still want to find the unitless values of mode shapes, and If I'm remembering it correctly, you can find them as follows.
Unitless modal displacement of a particular mode = total diaphragm displacement at a story for that mode / scale factor.

Where, the scale factor is nothing but,
(Modal Participation factor, L x
Spectral Accel. Sa)/(Sq. Of frequency of a mode, Wn^2)

This is driven from the following equation.
= [phi] x L/M* x Sa / wn^2

 

[Zouatine]

Thank you, Sir.