CSI ETABS - 11 - Modal Analysis Case [ Eigen or Ritz Vectors ] for Fundamental time period/frequency
ฝัง
- เผยแพร่เมื่อ 9 ก.ย. 2019
- In this lecture, Modal Analysis Case [ Eigen or Ritz Vectors ] is discussed.
DETAILS:
Modal analysis, or the mode-superposition method, is a linear dynamic-response procedure which evaluates and superimposes free-vibration mode
shapes to characterize displacement patterns. Mode shapes describe the configurations into which a structure will naturally displace. Typically, lateral
displacement patterns are of primary concern. Mode shapes of low-order mathematical expression tend to provide the greatest contribution to structural response. As orders increase, mode shapes contribute less, and are predicted less reliably. It is reasonable to truncate analysis when the number of mode shapes is sufficient.
A structure with N degrees of freedom will have N corresponding mode shapes. Each mode shape is an independent and normalized displacement pattern which may be amplified and superimposed to create a resultant displacement pattern.
Numerical evaluation proceeds by reducing the equations of motion (N simultaneous differential equations coupled by full mass and stiffness matrices) to a much smaller set of uncoupled second order differential equations (N independent normal-coordinate equations). The orthogonality of mode-shape relations enables this reduction.
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thank you..i have a question..what is maximum cycle when you defined load names like ux, uy and uz??
Thanks for the efforts you made. Pls Keep it up.
I have a question, In Etabs official tutorial training, them mention the mass participation ratio to be as closer to 1 as possible. in your video, you mentioned, above 90% should be good. so is building code or ASCE mentions above 90% for the mass participation ratio should be good? or what is the reason you mention 90%?
thank you
how can i get Phi value that is use in Eigen frequency analysis
Sir how to find that mode shape value?
very nice and clear presentation, sir 👍 with my vibration measurement company I'm normally focused on the experimental modal analysis as shown in some of my videos. Your video helped me to understand even more the simulation guys, for those I provide the acquired measurement datas in order to validate their simulation models. Keep it up!
In you daily business...do you use more Eigen or Ritz Vectors?
Thanks.... For your valuable feedback....
I don't have daily usage..
Where can i see mode shape cofficient ?
Thank you. Sir, how did you know that the target dynamic mass participation ratio is equal to 90?
code book
Sir, I have one question.
When we do moral analysis manually then for each direction say for x-axis we get no. of modes = no. of stories, but when we do it in Etabs or other softwares then how the no. of modes in each direction increase more than the no. of stories? It’s increase up to 3 times the no. of floors or even more. How and why exactly ? Why this difference in softwares and when we do it manually?
Please answer sir. It will really help me a lot
For the rubber isolator placed in a four storey building...how does mode shapes look...For me the isolator is displaced away from the axis...Is that right sir?
Yes
. It is right...
But isolater need to be designed
.... Properly
Does the time period change if only DL+LL is used?? Is applying lateral force compulsory to get time period???
Time period comes from... Mass Source... It is independent of lateral loads.
Respected sir, how to solve warning of solving linear stiffness from zero initial conditions, Numerical problems encountered during equation Assembly
same doubt man, let me know if you come across the solution
I am getting more moments in Ritz than eigen whats the reason sir
Please arrange your playlist...Pls don't mind...
what is the reason for 0 values in UX AND UY in mode 1 to 9?
Dear, When you hit or push anything , for example a steel rod... In the initial modes... it will give higher values... but after some vibrations ...
it tries to come to its orgional position... So that is why ... in higer modes the values of Ux and Uy are small or near to zeo.
One of the best explanation I've ever seen 👍👍
Thanks dear
Can you plz make videos on retaining wall design using prokon ?? I helps me a lot
@@manoharmanu6734 dear, i do not have command on prokon.
@@civilmdc so may I know on what softwares are you relying on ? For retaining wall ?
@@manoharmanu6734 ASDIP Retain
Sir, why are you looking sum of RX and not sum of UX to be >90%.
Thanks in advance.
Hello, sir. Is it possible that the model of three story building has time period at modal analysis until 1,6? I mean, it wasn't too large? i'm using modal analysis which eigen type. Did you know how to get the time period at 0,6-0,7 for that three story building?
Check your column heights and column cross section....
2nd bay lengths...
If they are large..... For example large column heights....
It can increase your... Time period
@@civilmdc i checked my column. At the first, the column height was 7,2 meters, then i cut until 5,15 meters. But, there's still same period. The problems is at the first mode of period time was too large, the second and etc was normal period or as my assumption by manually.
@@nurulfathiyyah688 you have to investigate each element closely..
Because your time period is too high.. than normal situations...
I think it in your model issue
Hello sir
I am also using this software I have a doubt on some points
1. If ETABS says all member passed with design check then should we have to check all time manually for each member.
2 . Etabs doesn't shows any crank bar on beam.
But on field I used many times by referring some good rcc books .
So can we go for crank or we can stick with top and bottom rebar
Hi dear,
1-Ans-when ETABS Says all checks have been passed.... It is okay..... But i recommend please go to display design info....... Select display all type of failures..... it will show, if any issue present in any beam....
2- Dear crank bar is old technique ....(which is called bent up curtailing method )
Now almost every engineer use curtailment technique... even ETABS use curtailment technique. So that is why ,,,, No crank bar.
@@civilmdc Thanks for clearing my doubts that will be very helpful for my future... Thanku
@@270sushil welcome
beautifully explained thank u so much sir from mumbai 🙏🙏🙏
Welcome
And brother thanks for appreciative feedback
Sir how can i solve "number of starting vectors reduced to=2" thanks for healp
Im having the same issue.. U got any solution?
how can i find modal cases menue in etabs v 20 please?
Go to Define menus... And load cases.
Then model cases
@@civilmdc thank u i could solve it 😀 i am very happy because i try to search for it from ten days ago
Nice video Sir.
The mode 1 value in Etabs analysis is 0.821 but manual analysis gives 0.42 .Is that right sir.
If so,could you please tell the reason behind that.Thanks.
In manual.... You adopted which method?
Response Spectrum method
Actually, it is a four story building, for the four modal values first mode value is 0.821 in etabs ,but rest 3 mode value are approximately same to manual calculation...the first value is the problem
As per the concepts,first value should be 10 percent of the number of stories...so I guess 0.82 is wrong...If not is there is any error to be rectified in etabs ie,should I have to edit any factor.Thanks
How can software analysis mode shape in 3d,how to do it in manual analysis ?
👍🏻
Sir for Underground water tank + ground floor,
I did Ritz analysis with dynamic. It is coming model participating mass ratio
@4th model
X direction- 17%
Y-direction- 98%
@5th model
X-direction 24%
Y-direction 99%
@6th model
X-direction 69%
Y-direction 99%
@7th model
X-direction 99%
Y-direction 99%
Is it correct?
I did not understand the objective of ur video. In description u said Eigen vs Ritz Vector but in the video there is no comparison.