I think there are 2 options more: 1. Geometry - Additional attributes - Load distribution. Just need to exclude main beams from load distribution. 2. Change slab direction from X-Y (2 directional) to either X or Y (1 directional. But you probably knew it anyway) Thanks
I changed the title of the video to better reflect the topic. Thank you very much for your suggestion, it helped improve the video Keep being awesome (New title is now: Structural Model Meshing and Load Transfer in Autodesk Robot)
Also, please note that, if you define your slab as 1 way or 2 way (trapezoid and triangles) from the floor definition window, you would lose the calculation of deflection in the slab.
hello Dr. CEE if there's one reason i love RSA its because i met your channel. Keep these coming. next you should organise a structures conference.😂😂😂😂 and we shall be there, your full classroom sir. thank you!!
Oh! that is amazing to hear! thnx a lot really. I do appreciate your words and hope that you keep enjoying the content. I might be travelling next year to some conferences around the world (I am an Assistant Professor in Civil Engineering, so I have to publish original research) I will keep you posted about that Thnx a lot for your encouragement. If possible, please share this channel and videos with your friends. Regards, CEE
Dear CEE, Thank you very much for your sharing, this video is very helpful to junior engineer like me which learn how to Autodesk Robot. Hope to see more video like this more as it possible. Best regards, 🙏🙏🙏
Hi there! 👋 I’ve been really enjoying your content on Civil Engineering Essentials. Your tutorials are incredibly insightful, and I appreciate how you break down complex concepts, Could you consider creating a tutorial about castellated and cellular steel beams according to Eurocode
Hello ^_^ thnx a lot for your comment, I am really honored. Not sure if Robot has cellular beams and co, but let me check and get back with a video if possible. Oh one thing, if possible, please share the channel with your friends, it helps a lot. Regards, CEE
Hello CEE, Modelling pitfalls indeed. It also feels like I may be under or over thinking some of the things here. MAIN BEAMS: If I use the “odd physical separation method” or the “FE meshing generation method” I get a set of shear force distribution (Fz) values on the main beams that are on average about 15% (give or take) lower than the average Fz values that I get on the main beams from using either “cladding” or “slab edges linear releases” or even “unidirectional slab behaviour mimicked by using an orthotropic slab thickness definition” Should one “swallow the pill” and accept that any of the above methods could be ok to use to calculate the forces for the design of the main beams? SECONDARY BEAMS: If I consider the shear force distribution (Fz) on the other three secondary beams, it appears that it is only through the use of “cladding” that gives results of the shear force distribution (Fz) of the middle secondary beam to be about double that of the outer secondary beams. The other “methods” that were noted above for me did not have Fz values for the middle beam as about double that of the outer beams. Why would this be? Isn’t the middle beam supposed to be about twice as loaded by the slab? RC SLAB: If I were to consider say a 1-meter-wide slab strip in the direction perpendicular to the three secondary beams; could I liken that slab strip to say a “two spans continuous beam” that is supported on the three secondary beams? and if so, could I then expect the slab strip to have “sagging bending moments” between the secondary ends beams and the secondary middle beam and to have “hogging bending moment” over the secondary middle beam “support”? I am asking the above because the “panel cut” that I made in RSAP through the slab over the three secondary beams seem to be indicating overall “sagging bending moments” on the slab across the three secondar beams, the slab is essentially “sagging” along with the middle secondary beam that “supports” it. This behaviour is resulting is a situation where the slab strip is behaving more like a “one span simply supported beam” as opposed to a “two spans continuous beam”. Thank you for the video. It is always a pleasure to watch and learn from your work Kind regards, DK
Hello there dear Engr. DK! sorry for the late reply, I do love reading every letter in your comments and pinning those, so let's see: true, there are differences between this offsetting and cladding (and co) ideas. I think this is partly due to us adding new objects that do deflect and rotate, draining parts of the total energy in the system (because external work of forces must equal internal work of elements). This might cause the difference. oh the difference is because if you are using a shell to model the structure, then the shell itself will displace downwards, once again taking a part of the total work / energy applied by the external forces. about overall sagging moment: oooooooooooh this is lovely! Here is a cool thing so please end follow me with this one: (Beast Mode On!) First, you are right. You are saying that the strip on the slab should look like this: ||======||======|| which leads to zero moment on the edges, and a negative moment (hogging moment) above the support. You are 100% right in your assumption. Now here is the caveat: this only works if the supports are "real supports" and do not move down. However your slab is supported by beams, which can themselves move down. Now let me read your mind: you are saying: wait a minute! why then was it always the case that I get the sagging moments and hogging moments exactly as they are and never had to think about it? Because the stiffness of the beams was sufficient for its deflection to be small relative to the deflection of the slab. In this video, I admit I did not pay attention to those while trying to show my point of being able to use shells "which provide displacement calculations" to model this odd structure. I also wanted - but actually forgot - to show that this can be used to model a slab supported by 3 beams in a |_| formation (3 sides supported) but forgot. That is on me ^_^ Now wait, beast mode is not done yet. Here are some ideas I want to uncover since we went to this discussion. For that, please clc shift+delete the structural model I discussed above and lets start a new model. a simple slab. ======== || || || ======== So two spans in the x, 1 span in the y (I hope those lines I draw are undersandable on YT). when you analyze this slab which is supported by beams, and open the moments in the x-strip, you get the usual pattern right? Now wasn't it odd that: if you take a panel cut in the middle, the values are different than those of the further above or below the middle? Also, isn't it strange the the hogging models rise sharper near the columns (not above them, I am not talking about the stress concentration of the column itself). This is related to the beam deflecting more in the middle of the span than above the column. Now you can make a nice little trick and modify the beam by decreasing the section inertia. See how the slab would change itse behavior? Hope this openes some new ideas ^_^ Thank you very much! You are the best Regards, CEE
Dr.CEE, such cases what if u do make a one way slab ....with the load distribution towards the secondary beams....as the principles of load transfer outlines in steel strucutres?? From slab to secondary beams then to primary beams ...
Also, please note that, if you define your slab as 1 way or 2 way (trapezoid and triangles) from the floor definition window, you would lose the calculation of deflection in the slab.
You mention that the beam is discretized 8:10 May I ask how does the FEM work here? Why do we need to set up all those settings for 2D elements, but when it comes to 1D elements (beams, columns) there is no setting required and we get a beautiful curved diagram? Thank you for your time :) All the best!
Oh, that is a good question: The curve you get from linear shapes is actually a lie ^_^ The reason why is: when the analysis is complete, all you get are actually the displacements and rotations of the start and end point of the linear elements. Now your question is: Ok so why do we get a nice curve? if we only have two points? It is because RSA (and the FEM in general) do a little trick here, you see, there is something called "shape functions". Ok, this may be a longer explanation: Let's say you have a beam S------------------------E where S is the start and E is the end and assume you want to "approximate" the deflection at distance x from the start S--------|x|------------E The only thing you have from the FE analysis are the displacements and rotations of S and E, you do not directly have the displacement (or rotation) of point x. The way it is done is: displacement at x = N1u1+N2u2+N3r1+N4r2 u1 and u2 are the displacements of the start and end (you have those from the FE analysis) r1 and r2 are the rotations of start and end (you have those from the FE analysis) N1 is a function in -------- wait for it------ x. N2, N3, N4 are also function of x This means that: if you have a certain x, then you can find N1 N2 N3 N4 and use them to find displacement at x This is exactly the lie autodesk robot uses to "show" a nice curve. It evaluates this at multiple distances x from the start. I hope it helped. CEE
@@CivilEngineeringEssentials Fine method we have at our disposal. (fine...ite method - wink wink) I compared 2 situations (1 continuous beam vs. 2 half beams) at the same position: S----------x---------E vs. S-------ES-------E The x possition of the first beam and the common point of the other two show the same displacement and moment. This, of course, I observed throughout my years as working in design engineering. However, your explenation really puts the background of how this works into the spotlight. I applaud you for all the great work you put into this channel, for your extraordinary knowledge in the field and for your ability to explain it all!
Thank CEE. Your tutorial has really help me a lot for my design. God bless u. Please I noticed there in no "moving Load" in 2024 version of Robot structural designer. How can I go about it plss? And 2022 version does not hv load combination: 5950. Please help me out.
Hello there, omg you are right. I just checked it, I could not find it! I will check out how to get this back and get back to you with details (if this feature is still available) Regards, CEE
Hi, I would like to ask what is your snapping setting which allows you to snap on some points so accurately under ‘View’ settings. As right now, I can only click on certain points in the ‘plan’ view according to my axis.
Great video. Is it just nesting the slab which the video relates to? Just a thought, As to define load just going to one beam could you not just define the slab as a one-way slab load distribution element? Or click on the beam type in bottom left hand corner and which to ignore this beam in the analysis?
Yep, it was to explain how you can manipulate meshing to your benefit. You can generalize this on other scenarios. Btw, heads up: next video is about the feature: load take down analysis. 👍 Also, your suggestion would work too.
I changed the title of the video to better reflect the topic. Thank you very much for your suggestion, it helped improve the video Keep being awesome (New title is now: Structural Model Meshing and Load Transfer in Autodesk Robot)
I might be on the wrong here, and would also like to hear your opinion about it, but wouldnt 'offsets' make a solution for the loading path according to the figure you were trying to model?
Besides the other ideas mentioned in the pinned comment, I'm not sure about offsets. Offsets have a strange tendency to create a zigzaggy moment on the beam if a slab is connected. I have to check it myself before I can give a definite answer. I think I have a video about offsets, but it does not include slabs in the model. Still thnx a lot for you comment, it really makes me happy to see your thoughts on my videos 👍
I have noted that exact same pattern you described in some of my modeling aswell, trully offsets are to be taken with preliminary cautions. Thank you for the response back, keep up the good work !@@CivilEngineeringEssentials
True. I guess it is because offsetting is done via a rigid link between the slab and the beam, which has a stiffness, which causes extra moments when subjected to horizontal loads. I agree with you, offsets should be used carefully. You are most welcome. I always enjoy discussing those points with all of you. Regards, CEE
Totally ok. I tried to show how you can manipulate meshes to do this too. I think I have a video about 1 way slabs on this channel. 1 issue though, if you do a simple 1 way cladding, then you wont be able to get the displacement of the shell and its internal loads.
Also, please note that, if you define your slab as 1 way or 2 way (trapezoid and triangles) from the floor definition window, you would lose the calculation of deflection in the slab.
I think there are 2 options more:
1. Geometry - Additional attributes - Load distribution. Just need to exclude main beams from load distribution.
2. Change slab direction from X-Y (2 directional) to either X or Y (1 directional.
But you probably knew it anyway)
Thanks
You r right bout ur other options. I intended to talk about meshing in this vid and other ideas. I pinned ur comment to the top
I changed the title of the video to better reflect the topic. Thank you very much for your suggestion, it helped improve the video
Keep being awesome
(New title is now: Structural Model Meshing and Load Transfer in Autodesk Robot)
Also, please note that, if you define your slab as 1 way or 2 way (trapezoid and triangles) from the floor definition window, you would lose the calculation of deflection in the slab.
hello Dr. CEE if there's one reason i love RSA its because i met your channel. Keep these coming. next you should organise a structures conference.😂😂😂😂 and we shall be there, your full classroom sir. thank you!!
Oh! that is amazing to hear! thnx a lot really. I do appreciate your words and hope that you keep enjoying the content.
I might be travelling next year to some conferences around the world (I am an Assistant Professor in Civil Engineering, so I have to publish original research) I will keep you posted about that
Thnx a lot for your encouragement. If possible, please share this channel and videos with your friends.
Regards,
CEE
I love this old school rsap videos!!
I want to keep a balance between those and the series ❤️🌹
Dear CEE, Thank you very much for your sharing, this video is very helpful to junior engineer like me which learn how to Autodesk Robot. Hope to see more video like this more as it possible.
Best regards, 🙏🙏🙏
You are most welcome. Yes, more robot videos are coming so stay tuned 🌹
Hi there! 👋 I’ve been really enjoying your content on Civil Engineering Essentials. Your tutorials are incredibly insightful, and I appreciate how you break down complex concepts, Could you consider creating a tutorial about castellated and cellular steel beams according to Eurocode
Hello ^_^ thnx a lot for your comment, I am really honored.
Not sure if Robot has cellular beams and co, but let me check and get back with a video if possible.
Oh one thing, if possible, please share the channel with your friends, it helps a lot.
Regards,
CEE
@@CivilEngineeringEssentials Thanks , I always do this. Your channel is very useful
Hello CEE,
Modelling pitfalls indeed. It also feels like I may be under or over thinking some of the things here.
MAIN BEAMS:
If I use the “odd physical separation method” or the “FE meshing generation method” I get a set of shear force distribution (Fz) values on the main beams that are on average about 15% (give or take) lower than the average Fz values that I get on the main beams from using either “cladding” or “slab edges linear releases” or even “unidirectional slab behaviour mimicked by using an orthotropic slab thickness definition”
Should one “swallow the pill” and accept that any of the above methods could be ok to use to calculate the forces for the design of the main beams?
SECONDARY BEAMS:
If I consider the shear force distribution (Fz) on the other three secondary beams, it appears that it is only through the use of “cladding” that gives results of the shear force distribution (Fz) of the middle secondary beam to be about double that of the outer secondary beams. The other “methods” that were noted above for me did not have Fz values for the middle beam as about double that of the outer beams. Why would this be? Isn’t the middle beam supposed to be about twice as loaded by the slab?
RC SLAB:
If I were to consider say a 1-meter-wide slab strip in the direction perpendicular to the three secondary beams; could I liken that slab strip to say a “two spans continuous beam” that is supported on the three secondary beams? and if so, could I then expect the slab strip to have “sagging bending moments” between the secondary ends beams and the secondary middle beam and to have “hogging bending moment” over the secondary middle beam “support”?
I am asking the above because the “panel cut” that I made in RSAP through the slab over the three secondary beams seem to be indicating overall “sagging bending moments” on the slab across the three secondar beams, the slab is essentially “sagging” along with the middle secondary beam that “supports” it. This behaviour is resulting is a situation where the slab strip is behaving more like a “one span simply supported beam” as opposed to a “two spans continuous beam”.
Thank you for the video. It is always a pleasure to watch and learn from your work
Kind regards, DK
Hello there dear Engr. DK!
sorry for the late reply, I do love reading every letter in your comments and pinning those, so let's see:
true, there are differences between this offsetting and cladding (and co) ideas. I think this is partly due to us adding new objects that do deflect and rotate, draining parts of the total energy in the system (because external work of forces must equal internal work of elements). This might cause the difference.
oh the difference is because if you are using a shell to model the structure, then the shell itself will displace downwards, once again taking a part of the total work / energy applied by the external forces.
about overall sagging moment: oooooooooooh this is lovely! Here is a cool thing so please end follow me with this one: (Beast Mode On!)
First, you are right. You are saying that the strip on the slab should look like this:
||======||======||
which leads to zero moment on the edges, and a negative moment (hogging moment) above the support. You are 100% right in your assumption.
Now here is the caveat: this only works if the supports are "real supports" and do not move down. However your slab is supported by beams, which can themselves move down.
Now let me read your mind: you are saying: wait a minute! why then was it always the case that I get the sagging moments and hogging moments exactly as they are and never had to think about it?
Because the stiffness of the beams was sufficient for its deflection to be small relative to the deflection of the slab.
In this video, I admit I did not pay attention to those while trying to show my point of being able to use shells "which provide displacement calculations" to model this odd structure. I also wanted - but actually forgot - to show that this can be used to model a slab supported by 3 beams in a |_| formation (3 sides supported) but forgot. That is on me ^_^
Now wait, beast mode is not done yet. Here are some ideas I want to uncover since we went to this discussion. For that, please clc shift+delete the structural model I discussed above and lets start a new model.
a simple slab.
========
|| || ||
========
So two spans in the x, 1 span in the y (I hope those lines I draw are undersandable on YT).
when you analyze this slab which is supported by beams, and open the moments in the x-strip, you get the usual pattern right?
Now wasn't it odd that: if you take a panel cut in the middle, the values are different than those of the further above or below the middle?
Also, isn't it strange the the hogging models rise sharper near the columns (not above them, I am not talking about the stress concentration of the column itself). This is related to the beam deflecting more in the middle of the span than above the column.
Now you can make a nice little trick and modify the beam by decreasing the section inertia. See how the slab would change itse behavior?
Hope this openes some new ideas ^_^
Thank you very much! You are the best
Regards,
CEE
Dr.CEE, such cases what if u do make a one way slab ....with the load distribution towards the secondary beams....as the principles of load transfer outlines in steel strucutres?? From slab to secondary beams then to primary beams ...
I agree completely. This video wants to show how meshing can affect the load distribution.
Also, please note that, if you define your slab as 1 way or 2 way (trapezoid and triangles) from the floor definition window, you would lose the calculation of deflection in the slab.
You mention that the beam is discretized 8:10
May I ask how does the FEM work here? Why do we need to set up all those settings for 2D elements, but when it comes to 1D elements (beams, columns) there is no setting required and we get a beautiful curved diagram?
Thank you for your time :) All the best!
Oh, that is a good question:
The curve you get from linear shapes is actually a lie ^_^
The reason why is:
when the analysis is complete, all you get are actually the displacements and rotations of the start and end point of the linear elements.
Now your question is:
Ok so why do we get a nice curve? if we only have two points?
It is because RSA (and the FEM in general) do a little trick here, you see, there is something called "shape functions".
Ok, this may be a longer explanation:
Let's say you have a beam
S------------------------E
where S is the start and E is the end
and assume you want to "approximate" the deflection at distance x from the start
S--------|x|------------E
The only thing you have from the FE analysis are the displacements and rotations of S and E, you do not directly have the displacement (or rotation) of point x.
The way it is done is:
displacement at x = N1u1+N2u2+N3r1+N4r2
u1 and u2 are the displacements of the start and end (you have those from the FE analysis)
r1 and r2 are the rotations of start and end (you have those from the FE analysis)
N1 is a function in -------- wait for it------ x.
N2, N3, N4 are also function of x
This means that: if you have a certain x, then you can find N1 N2 N3 N4 and use them to find displacement at x
This is exactly the lie autodesk robot uses to "show" a nice curve. It evaluates this at multiple distances x from the start.
I hope it helped.
CEE
@@CivilEngineeringEssentials Fine method we have at our disposal. (fine...ite method - wink wink)
I compared 2 situations (1 continuous beam vs. 2 half beams) at the same position:
S----------x---------E vs. S-------ES-------E
The x possition of the first beam and the common point of the other two show the same displacement and moment. This, of course, I observed throughout my years as working in design engineering. However, your explenation really puts the background of how this works into the spotlight.
I applaud you for all the great work you put into this channel, for your extraordinary knowledge in the field and for your ability to explain it all!
Amazing
Thnx a lot
Thank CEE. Your tutorial has really help me a lot for my design. God bless u.
Please I noticed there in no "moving Load" in 2024 version of Robot structural designer. How can I go about it plss?
And 2022 version does not hv load combination: 5950. Please help me out.
Hello there,
omg you are right. I just checked it, I could not find it!
I will check out how to get this back and get back to you with details (if this feature is still available)
Regards,
CEE
@@CivilEngineeringEssentials thank you so much. I will look forward to hearing from you. Best regard.
Hi, I would like to ask what is your snapping setting which allows you to snap on some points so accurately under ‘View’ settings. As right now, I can only click on certain points in the ‘plan’ view according to my axis.
just waiting for it
There is much more. Gonna ramp up video production 🌹
Great video. Is it just nesting the slab which the video relates to? Just a thought, As to define load just going to one beam could you not just define the slab as a one-way slab load distribution element? Or click on the beam type in bottom left hand corner and which to ignore this beam in the analysis?
Above was suppose to read meshing not nesting
Yep, it was to explain how you can manipulate meshing to your benefit.
You can generalize this on other scenarios.
Btw, heads up: next video is about the feature: load take down analysis. 👍
Also, your suggestion would work too.
I changed the title of the video to better reflect the topic. Thank you very much for your suggestion, it helped improve the video
Keep being awesome
(New title is now: Structural Model Meshing and Load Transfer in Autodesk Robot)
I might be on the wrong here, and would also like to hear your opinion about it, but wouldnt 'offsets' make a solution for the loading path according to the figure you were trying to model?
Besides the other ideas mentioned in the pinned comment, I'm not sure about offsets. Offsets have a strange tendency to create a zigzaggy moment on the beam if a slab is connected. I have to check it myself before I can give a definite answer. I think I have a video about offsets, but it does not include slabs in the model.
Still thnx a lot for you comment, it really makes me happy to see your thoughts on my videos 👍
I have noted that exact same pattern you described in some of my modeling aswell, trully offsets are to be taken with preliminary cautions.
Thank you for the response back, keep up the good work !@@CivilEngineeringEssentials
True. I guess it is because offsetting is done via a rigid link between the slab and the beam, which has a stiffness, which causes extra moments when subjected to horizontal loads.
I agree with you, offsets should be used carefully.
You are most welcome. I always enjoy discussing those points with all of you.
Regards,
CEE
What about one-way spanning slabs?
Totally ok. I tried to show how you can manipulate meshes to do this too.
I think I have a video about 1 way slabs on this channel.
1 issue though, if you do a simple 1 way cladding, then you wont be able to get the displacement of the shell and its internal loads.
Also, please note that, if you define your slab as 1 way or 2 way (trapezoid and triangles) from the floor definition window, you would lose the calculation of deflection in the slab.