Hello CEE; This is a really nice and engaging video; it systematically brings out different ways of evaluating this kind of structural foundation. I like the “brick-by-brick” build-up approach that have been used to work through the topic. The tutorial makes me pause and think of the following: • It is quite clear that the ground beams (by themselves, without the help of a raft) are also capable of supporting light structural loads with reasonable (tolerable) values of elastic ground reactions underneath them beams. On the other hand, the introduction and integration of the raft to these ground beams does reduce and redistribute some of the ground beams original elastic ground reactions from the beams to the raft (and this is good news). • I suppose the designer has options here, the designer can decide (depending on the structure being designed and on the associated design loads, soil conditions, etc.) how much role the raft is required to play (or to contribute). 11:01 You are correct, there is a symbol (a display option) to show “Elastic foundation”, you can find it under “Model” subcategory in the display options. 12:46 Yes, I agree with both Mr. Editor and with Mr. Recorder on this, these are the kinds of real-life behaviours and construction issues that should be explored and discussed. Thank you for bringing this up and for discussing it. I also don’t think the structure should move in the X or in the Y direction. I suppose this is where one would have to define the other elastic foundation coefficients i.e. Ky and Hx? Unfortunately, the way in which the values of these other two coefficients are estimated is still fuzzy for me. Kz is relatively straightforward (after the extensive past and present work that have been done by the CEE of course). I hope in later videos, it will also become clearer how to estimate or how to work out the values of these other two elastic foundation coefficients. In the meantime, and just so to explore the point; I went ahead and input a value of (say) 1 unit for both Ky and Hx anyway (much like it was done before in the flexible method mat (raft) foundation video). This resulted in a “stable” structure. I know that by me randomly inputting unit values for these coefficients may possibly result in unintended consequences or unintended response by the structure especially in the X and Y directions (even the Z direction maybe?). As a small act of consolation, I have compared the values of the BM and SF obtained on the ground beams when there are unit values of Ky and Hx and when I have removed these unit values and used a “stabilising support” option that was suggested in this video by the CEE instead [kudos for that idea by the way]. I have found that both BM and SF values in both scenarios compare well and thus the structure response in the Z direction seem to be less sensitive to the unity coefficient values that I had used for now. As a side note, I have also noticed that RSAP will still give a warning calculation message that says “No support” after one runs the analysis on a structure that is supported only on a foundation that is defined by use of elastic foundation coefficients. This warning message remains so even when all elastic foundation coefficients have been defined and the structure is stable. This message only goes away when one defines and assign any one of the supports under the supports dialog box. I find this strange because I had “presumed” that assigning “elastic foundation coefficients” would be taken as assigning a kind of a structural support? 19:22 This version looks like it is working as far as I am concerned. The modelling ideas are rational and solid; and the results seems to make sense. 21:05 lol Another side note from me: Following on from this tutorial and from the past mat (raft) foundation tutorial; both the modelling, loading, and analysis of beams or even slabs on elastic supports in RSAP is no longer a problem, it is now clear how to do this and it is readily doable. With my newly acquired confidence 😊, I have since attempted to run “verification examples” by modelling and analysing (in RSAP) some already solved beams or slabs on elastic supports example problems and comparing the results that I get from RSAP with the results from these existing verification example problems. I have been getting mixed answers, sometimes the examples verify as expected and sometimes not. I admit that my search for verification examples has not been that profound and I intend to continue with this exercise so that I can make informed decisions on this. I’d suggest that if the CEE does decide to dive deeper into this, then perhaps consideration of some verification examples could be something to look at? Thank you for another engaging video. I have enjoyed this video and I am looking forward to the next CEE videos. Have a great day, Regards, DK
Hi there Engr. DK, yep, indeed, ground beams are capable of supporting structures as long as the bearing capacity is not exceeded. For the raft, it does help especially at positions near the columns. Thanks a lot for the hint with regard to the display options, it helped ^_^ With regard to other values, I think those questions warrant some "lecture/rsap video hybrid", as is the case in most "introductory videos" in the previous structure. And you are right, even putting a value of 1 in those stiffnesses causes stabilization of the structure. Here is some food for thought, the lateral stiffnesses are used to model pile foundations subjected to lateral loadings on its top. There is a dozen theories about this, and the book "Foundation" from Braja M Das should have something about this. Indeed, we use the horizontal stiffnesses - especially in research - when we want to model integrated bridges, and consider the soil structure interactions. I think I need to prepare something not as cryptic as research, but rather more practical. the no support thing might be a bug on behalf of robot. Funnily enough, when I was giving physical training courses in robot (back in 2010s), I was still a "baby instructor" holding only a BSc degree, at that stage I was usually stating that there is "actual" instability and "hypothetical" instability. A hypothetical instability is, for example, what you saw in Ux and Uy in that structure, as it - in reality - won't budge in those directions under the given loading conditions and size of structure. Please note that under more extreme loadings for bigger structures, this would not be the case. But in the end, such structures (towers) would be piled. You are right, this model (raft and beam) seems to make sense, but I still added the "disclaimer" in the video, as I want to dive deeper into verifications, exactly as suggested by you. This - of course - needs some time to check, double check, get the differences, if any, and explain those differences or find a solution to those. Once again, happy to have viewers like you. Regards, CEE
@@CivilEngineeringEssentials I got one question. Is it possible to build multistorey building with room size of 80ft x 80ft with no pillars in between. With wall or pillar support 80ft apart what should be thickness of walls and pillars to support and hold that huge slabs and multiple floors above it.
@@KING_DRANZER Yes, it is totally possible. It seems you want to have a cinema or a large auditorium for that regard. Still please note!!! the beam is going to be HUGE and the columns are going to be really extra stiff. If you are using a simply supported beam, then as per ACI code, your beam height should be at least L/16 which is 80/16 so 5 ft. This means that you are required to provide something called skin reinforcement as per the ACI provisions. For the column, here I do not really know. As the stiffness of the column (if you are having a frame) is going to affect the amount of moment it carries. Here a trial and error approach is to be adopted. But one rule of thumb is that the column should not be smaller than the beam. Because you want to have something called a strong column - weak beam connection for seismic provisions. Finally, having large columns could be a challenge in architectural terms. Especially because your auditorium is actually 80ft x 80ft with zero columns in between. If you want some nice food for thought, google: RC auditorium or RC details cinema. You will see some nice ideas for your request. I hope this helped. Regards, CEE
@@CivilEngineeringEssentials Anyway, thank you very much for the reply. Actually it is a very complex design. But I will try to explain it. What my plan has is Ground floor 3 rooms 80ft x 80ft in which the Hall and the Dining Room are double floor height at 28ft and the Kitchen is single height 13ft with Storage room above it. The floor above it will be of single floor height and will have lot many 30ft x 40ft guest rooms single floor height 13ft. With center area left for lounge or common area. Above that gonna be again three 80ft x 80ft partitions in which Master Bedroom Small and Gym and Entertainment area are single floor 13ft rooms while 3rd is for theater which extends to upper floor. Above that is again one 80ft x 80ft Master Bedroom main with two floor height at 28ft. And 40ft x 80ft x 28ft common area for sitting and stuff. The 120ft x 80ft x 28ft will be extension to theater. So yes very complex design can this be feasible at all.
Thanks for this video. Usually in our country isolated footings are introduced for a building coupled with concrete tie beam, is the procedure for the calculation is the same with this one or theres another way for the specific conditions, isolated footings with tie beams?
I will be talking about tie beams in another video. It is actually really easy. Just model a beam, add the loads (the column loads are not added in this case), add elastic foundation, and caculate.
and another question sir, do i need to put a support on a Slab on ground without UZ , even though i have already have a support on the column that is in a lower level with the slab. Or i just assign the soil pressure on the slab without putting any support? the context is the slab is on ground but in a diffrent level with the foundation, thanks
Firstly I would like to say you do awesome job on this channel! Could you please explain how to use buckling analysis properly in practice? Robot have a problem with division of FEM elements which makes incorrect results in comperasion with Euler equation. There is a few videos on RUclips, but only easy examples with doing additional nodes, where in more complicated structures it's really impractical.
Thank you for the amazing tutorial. If we supposed the raft foundation under the beams, then we can apply elastic foundation only on the raft foundation without applying in it on beams, because beams are part of the raft foundation 🤔, is it right sir ??
Hello there, You are most welcome. If you apply the elastic foundation on raft alone without beams, you would still get an "automatic" elastic foundation under the beams that are part of the raft.) Reason? Because when RSA performs the structural analysis, it meshes the raft with the beam (it generates points that are on both the beam and the raft) then applies the elastic foundation below those points (so now the beam is also elastically carried by the ground) The difference here is that, while the elastic foundation under the beam is a spring on a line, for a raft it is an area spring. So I can say that both ways are right. Regards, CEE
Hello CEE;
This is a really nice and engaging video; it systematically brings out different ways of evaluating this kind of structural foundation. I like the “brick-by-brick” build-up approach that have been used to work through the topic. The tutorial makes me pause and think of the following:
• It is quite clear that the ground beams (by themselves, without the help of a raft) are also capable of supporting light structural loads with reasonable (tolerable) values of elastic ground reactions underneath them beams. On the other hand, the introduction and integration of the raft to these ground beams does reduce and redistribute some of the ground beams original elastic ground reactions from the beams to the raft (and this is good news).
• I suppose the designer has options here, the designer can decide (depending on the structure being designed and on the associated design loads, soil conditions, etc.) how much role the raft is required to play (or to contribute).
11:01 You are correct, there is a symbol (a display option) to show “Elastic foundation”, you can find it under “Model” subcategory in the display options.
12:46 Yes, I agree with both Mr. Editor and with Mr. Recorder on this, these are the kinds of real-life behaviours and construction issues that should be explored and discussed. Thank you for bringing this up and for discussing it. I also don’t think the structure should move in the X or in the Y direction. I suppose this is where one would have to define the other elastic foundation coefficients i.e. Ky and Hx?
Unfortunately, the way in which the values of these other two coefficients are estimated is still fuzzy for me. Kz is relatively straightforward (after the extensive past and present work that have been done by the CEE of course). I hope in later videos, it will also become clearer how to estimate or how to work out the values of these other two elastic foundation coefficients.
In the meantime, and just so to explore the point; I went ahead and input a value of (say) 1 unit for both Ky and Hx anyway (much like it was done before in the flexible method mat (raft) foundation video). This resulted in a “stable” structure. I know that by me randomly inputting unit values for these coefficients may possibly result in unintended consequences or unintended response by the structure especially in the X and Y directions (even the Z direction maybe?). As a small act of consolation, I have compared the values of the BM and SF obtained on the ground beams when there are unit values of Ky and Hx and when I have removed these unit values and used a “stabilising support” option that was suggested in this video by the CEE instead [kudos for that idea by the way]. I have found that both BM and SF values in both scenarios compare well and thus the structure response in the Z direction seem to be less sensitive to the unity coefficient values that I had used for now.
As a side note, I have also noticed that RSAP will still give a warning calculation message that says “No support” after one runs the analysis on a structure that is supported only on a foundation that is defined by use of elastic foundation coefficients. This warning message remains so even when all elastic foundation coefficients have been defined and the structure is stable. This message only goes away when one defines and assign any one of the supports under the supports dialog box. I find this strange because I had “presumed” that assigning “elastic foundation coefficients” would be taken as assigning a kind of a structural support?
19:22 This version looks like it is working as far as I am concerned. The modelling ideas are rational and solid; and the results seems to make sense.
21:05 lol
Another side note from me: Following on from this tutorial and from the past mat (raft) foundation tutorial; both the modelling, loading, and analysis of beams or even slabs on elastic supports in RSAP is no longer a problem, it is now clear how to do this and it is readily doable.
With my newly acquired confidence 😊, I have since attempted to run “verification examples” by modelling and analysing (in RSAP) some already solved beams or slabs on elastic supports example problems and comparing the results that I get from RSAP with the results from these existing verification example problems. I have been getting mixed answers, sometimes the examples verify as expected and sometimes not. I admit that my search for verification examples has not been that profound and I intend to continue with this exercise so that I can make informed decisions on this.
I’d suggest that if the CEE does decide to dive deeper into this, then perhaps consideration of some verification examples could be something to look at?
Thank you for another engaging video. I have enjoyed this video and I am looking forward to the next CEE videos.
Have a great day,
Regards, DK
Hi there Engr. DK,
yep, indeed, ground beams are capable of supporting structures as long as the bearing capacity is not exceeded. For the raft, it does help especially at positions near the columns.
Thanks a lot for the hint with regard to the display options, it helped ^_^
With regard to other values, I think those questions warrant some "lecture/rsap video hybrid", as is the case in most "introductory videos" in the previous structure.
And you are right, even putting a value of 1 in those stiffnesses causes stabilization of the structure.
Here is some food for thought,
the lateral stiffnesses are used to model pile foundations subjected to lateral loadings on its top. There is a dozen theories about this, and the book "Foundation" from Braja M Das should have something about this.
Indeed, we use the horizontal stiffnesses - especially in research - when we want to model integrated bridges, and consider the soil structure interactions. I think I need to prepare something not as cryptic as research, but rather more practical.
the no support thing might be a bug on behalf of robot. Funnily enough, when I was giving physical training courses in robot (back in 2010s), I was still a "baby instructor" holding only a BSc degree, at that stage I was usually stating that there is "actual" instability and "hypothetical" instability. A hypothetical instability is, for example, what you saw in Ux and Uy in that structure, as it - in reality - won't budge in those directions under the given loading conditions and size of structure. Please note that under more extreme loadings for bigger structures, this would not be the case. But in the end, such structures (towers) would be piled.
You are right, this model (raft and beam) seems to make sense, but I still added the "disclaimer" in the video, as I want to dive deeper into verifications, exactly as suggested by you. This - of course - needs some time to check, double check, get the differences, if any, and explain those differences or find a solution to those.
Once again, happy to have viewers like you.
Regards,
CEE
@@CivilEngineeringEssentials I got one question. Is it possible to build multistorey building with room size of 80ft x 80ft with no pillars in between. With wall or pillar support 80ft apart what should be thickness of walls and pillars to support and hold that huge slabs and multiple floors above it.
@@KING_DRANZER Yes, it is totally possible. It seems you want to have a cinema or a large auditorium for that regard.
Still please note!!! the beam is going to be HUGE and the columns are going to be really extra stiff.
If you are using a simply supported beam, then as per ACI code, your beam height should be at least L/16 which is 80/16 so 5 ft. This means that you are required to provide something called skin reinforcement as per the ACI provisions.
For the column, here I do not really know. As the stiffness of the column (if you are having a frame) is going to affect the amount of moment it carries. Here a trial and error approach is to be adopted. But one rule of thumb is that the column should not be smaller than the beam. Because you want to have something called a strong column - weak beam connection for seismic provisions.
Finally, having large columns could be a challenge in architectural terms. Especially because your auditorium is actually 80ft x 80ft with zero columns in between.
If you want some nice food for thought, google: RC auditorium or RC details cinema.
You will see some nice ideas for your request.
I hope this helped.
Regards,
CEE
@@CivilEngineeringEssentials Please can I share the 3D design with you to check its feasibility. If possible. Please can you look into it.
@@CivilEngineeringEssentials Anyway, thank you very much for the reply. Actually it is a very complex design. But I will try to explain it. What my plan has is Ground floor 3 rooms 80ft x 80ft in which the Hall and the Dining Room are double floor height at 28ft and the Kitchen is single height 13ft with Storage room above it.
The floor above it will be of single floor height and will have lot many 30ft x 40ft guest rooms single floor height 13ft. With center area left for lounge or common area.
Above that gonna be again three 80ft x 80ft partitions in which Master Bedroom Small and Gym and Entertainment area are single floor 13ft rooms while 3rd is for theater which extends to upper floor.
Above that is again one 80ft x 80ft Master Bedroom main with two floor height at 28ft. And 40ft x 80ft x 28ft common area for sitting and stuff. The 120ft x 80ft x 28ft will be extension to theater.
So yes very complex design can this be feasible at all.
Great video. Elastic foundation symbol can be found in Display=>Model, just under Releases
Thanks a lot ^_^.
For some reason, it escaped my mind. Thnx a lot.
Nice tutorial, thank you
Most welcome. Stay tuned for more content.
Also, if possible, suggest this channel to your friends ^_^
Regards,
CEE
yOU%RE THE BEST
most welcome. Happy those videos help.
Thanks for this video.
Usually in our country isolated footings are introduced for a building coupled with concrete tie beam, is the procedure for the calculation is the same with this one or theres another way for the specific conditions, isolated footings with tie beams?
I will be talking about tie beams in another video. It is actually really easy. Just model a beam, add the loads (the column loads are not added in this case), add elastic foundation, and caculate.
@@CivilEngineeringEssentials thank you, i will wait for that tutorial about footings with tie beams.
is there any new video of this? that you have checked its the right way, thanks
em,, if possible, could you provide more context of the question? you mean the ground beams?
i mean u mention u are not sure with that modelling and u need to check the calculation, if its right like on the real ones
and another question sir, do i need to put a support on a Slab on ground without UZ , even though i have already have a support on the column that is in a lower level with the slab. Or i just assign the soil pressure on the slab without putting any support? the context is the slab is on ground but in a diffrent level with the foundation, thanks
Firstly I would like to say you do awesome job on this channel! Could you please explain how to use buckling analysis properly in practice? Robot have a problem with division of FEM elements which makes incorrect results in comperasion with Euler equation. There is a few videos on RUclips, but only easy examples with doing additional nodes, where in more complicated structures it's really impractical.
Thank you very much for your comment.
Sure, I will take a look at it and post a video 'bout it if I find a practical way to do it.
Regards,
CEE
Thank you for the amazing tutorial.
If we supposed the raft foundation under the beams, then we can apply elastic foundation only on the raft foundation without applying in it on beams, because beams are part of the raft foundation 🤔, is it right sir ??
Hello there,
You are most welcome. If you apply the elastic foundation on raft alone without beams, you would still get an "automatic" elastic foundation under the beams that are part of the raft.) Reason? Because when RSA performs the structural analysis, it meshes the raft with the beam (it generates points that are on both the beam and the raft) then applies the elastic foundation below those points (so now the beam is also elastically carried by the ground)
The difference here is that, while the elastic foundation under the beam is a spring on a line, for a raft it is an area spring.
So I can say that both ways are right.
Regards,
CEE