Dynamic Analysis of Structures: Introduction and Definitions - Natural Time Period and Mode Shapes
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- Опубліковано 7 чер 2024
- In this video, Dynamic Structural Analysis is introduced.
The difference between Dynamic and Static analysis of structures is explained.
The main concepts and definitions related to dynamic analysis are explored such as the natural time periods, the natural frequencies and mode shapes.
The meaning of shear frames as used in dynamic analysis literature is explained and the difference between Single degree of Freedom and Multiple Degrees of Freedom Systems is shown.
The main methods used in Structural Dynamic analysis are briefly introduced such as the Time History Analysis and the Modal Analysis
This might be one of the greatest video on vibration that UA-cam have upload ever! THANKS!
Simple and very important video, thank you doctor NAFIE for sharing such great information in such a very good presentation
I'm glad to find this peice of treasure. It helped a lot with my paper work
WOW! An amazing piece of presentation. You just summarized my 4 months of semester in just a single video! Great visuals! Thanks for sharing such great information in such a beautiful presentation!
Thank you for comments and I am glad you liked the presentation.
Perfect presentation congratulations
very well explained, thank you it was really helpful
Dear Dr Nafie, thank you for your time and effort to create such excellent lectures. Your explanations and visual presentations are outstanding.
I am pleased the video was helpful to you
Totally agree!!!
Excellent video, very understandable presentation and great speaking pace.
I did not realized that the video was 14 minutes long. It passed really fast for me, I was very into the lecture.
Glad it was helpful!
Best video explaining Dynamic Structural Analysis. Simple, Direct, and Efficient. Thank You :) :)
Thank you for the nice comment
Explication topissime d'un professeur topissime Merci!
Thank you
Thank you sir for this video. It helped me a lot. Great presentation.
I am glad it helped
Wow! Earthquake engineering simplified. Great lesson.
I am glad it was helpful
Great explanation Professor!
Thank you for the nice comment
Excellent explanation professor!!
Thank you for the nice comment
thank you very much for your time and efforts
Thank you for the nice comment
I don't know how to express my respect and thanks to you...wonderful explanation!! Just One request from my side- keep posting more videos, Sir.
Thank you. God willing I will do my best
@@drnafie-structuralengineer4620 Sir, I'm really glad that you replied to my comment. May I please know how can I contact with you for knowing more about effective learning style? May I contact with you via email if you don't mind, Sir?
You can send me on this email:
drnafiestructures@gmail.com
Perfect tutorial, thank you.
Thanks.
Your work is awesome Dr. Please keep it like that.
Do you have any dynamic structures lectures please?
May god bless you for your good intentions. Very good video.
Thank you
Great video! Thank you!
Thank you very much for the compliments
Nice explanation with dynamic figures .
I am glad the video was helpful
Great Lesson, easy to understand it will be great if you have your own channel that we can learn more from you. God bless you
Thanks for the Compliment
I already have my own channel
ua-cam.com/channels/36hwM1et2Psl__WTJuHCHQ.html
very well presented, thank you sir
Glad it was helpful!
great lesson, it opened my eyes to a lot of issues. will you do a lecture on response spectra?
thnaks
Thank you for the nice comment
Of Course it is in my plans to talk about the response spectrum and seismic design.
That's why I put the dynamic analysis video in a separate playlist.
However, lately I got extremely busy. God willing, I will resume posting video when my time permits.
sir i want to know about the developing the fragility curve .can u share any materials
Thanks for the clear explanation sir
I am glad it helped
Great video!!! Only crux ❤️
I am glad the video was useful
Professor,
Do you have similar videos for Fourier series and laplace transforms.?
Unfortunately I don't
Thank you very much for this very clear explanation. May God bless you.
1 - Please How can we physically interpret the distance between frequencies? i.e. why sometimes the value of the frequencies rise very quickly and sometimes they are too close together?
Example :
(simulation result 1 :
freq 1 = 7 hz
freq 2 = 7.1 hz
freq3 = 7.14 hz
..
freq 20 =10.5 hz )
(simulation result 2 :
freq 1 = 7 hz
freq 2 = 16 hz
freq3 = 54.5 hz
..
freq 20 =700.96 hz )
What explains this difference which results from a variation in the dimensions of the structure? How can this difference be used? How is it useful? i.e. where is the advantage, in structure 1 or 2?
Thank you
Thank you for you encouraging comments.
Regarding your question, the mode shapes is mainly dependent on the distribution of stiffness and mass in the structure. You can change the modal frequencies by increasing the column dimensions in one story or adding mass in that story.
Regarding the distance between the frequencies, there is no clear cut answer to your question. Usually the mode shapes gives you information about the integrity of your model. For Example if I find 2 modes with very near frequencies but one mode is in the X direction and the other in the Y direction, this is not a bad sign, this only indicates that the stiffness in the X and Y directions are nearly equal. On the other hand if the 2 modes with very near frequencies are in the same direction this might indicate a problem such as an irregularity
In general, if we are dealing with regular buildings and considering only one direction I would expect mode shapes with frequencies that are not very near ( 1 or 2%) and not also very far.
In summary, if the mode shapes are very close, this is would require more inspection to find the reason for this and find if this is a disadvantage or a problem with the structure.
@@drnafie-structuralengineer4620 Thank you very much It's clear. I am extremely grateful for your valuable answer and time.
Best ever.
Thanks
Thank you
You're welcome
Thanks 🙏
I am glad the video was helpful
2- Why is it that in the literature authors often look only for the 6 or 10 first modes of a structure to study its dynamic characteristics? Are they more likely than others to occur?
When an initial displacement is applied, does the structure deform on all these first frequencies or only on the fundamental frequency? Thank you
The mode shapes are ordered by the lower to the higher frequencies. The low frequency mode is the softer mode. Usually each mode has an importance in the behavior that can be measured by the mass participation ratio as explained in the video.
Higher modes tend to be less important in the response of the structure than lower modes. The code requires that we include a number of modes that captures at least 90% of the response. Suppose that mode 1 constitutes 40% of the response, mode 2 40% and mode 3 5%, then these 3 will not be enough as they will constitute 85% which is less than 90%. We need to add more modes to the behavior until the sum of the participation mass ratios exceeds 90%.
When an initial displacement is applied to the structure, the structure will chose the mode shape (or shapes) that is closer to the shape of this initial deflection and will vibrate in it.
@@drnafie-structuralengineer4620 Yes, in fact, the small modes dominate the response, but I have trouble understanding why? Is it a finding from experience or is it a triviality I missed in the course? I know the displacements are bound to be small? But if these high frequencies with small displacements coincide with an frequencies of external load, won't that amplify the response as it is the case for small frequencies? An example from my structure which is a large pipe of a regular shape with axisymmetrical boundary conditions and loads : the high frequency modes are the most prominent in terms of Mass participation factor. (Mode 742 = 690 Hz have MPF= 26%) followed by (Mode 1= 14 Hz which have MPF = 16%) followed by (mode 2060 = 1500 Hz have MPF =6 %). The others first order modes have MPF close to zero . Could you help me interpret this? Is it a simulation problem on the part of the calculator (Ansys)? I had read somewhere that these calculators do not predict frequencies correctly above a certain threshold. Is it possible that this is a calculation error? Thank you very much for your patience
@@manalmorocco2262 Manal merci pour le partage et je sais où te trouver :D stp pose lui cette question sur l'amortissement j'ai assez galéré
All what we explain here is about buildings and any structures that behaves like buildings. So the rule that the softer first modes have more participation is for regular "buildings". Whether this will happen in the pipe problem or not, you have to analyze and study.
In order to help you, I will explain why this happens in a building. A mode will have high participation when most of the mode is moving toward a single direction, and this usually happens in the first modes of the regular buildings.
I don't know what exactly are you researching, but it seems to me that an axisymmetric pipe will generate limited mode shapes, because you only get the symmetric mode shapes . In my opinion you miss influential mode shapes that are not symmetric.
@@drnafie-structuralengineer4620 Oh I see more clearly now I don't know how to thank you Professor , really you helped us a lot. Allah ijazek bikhir
If you give all about dynamic vs static analysis in high rise building related book, it would be better.
I hope I will have the time to add more content
Sir response spectrum method?
You can watch this new video on the response Spectrum Method
ua-cam.com/video/setphyUnUu4/v-deo.html
Assalamualaikum sir, Can you also make video on wind analysis?
InShaa Allah, I will put it in my schedule for upcoming videos.
9:06 Lmao!!!
I hope the video was helpful
ez
I am glad it helped