Modeling Mat (Raft) Foundations (Flexible Method) in Autodesk Robot

[@niisarpei3676]

Great and informative tutorial as usual from the Civil Engineering Essentials Channel. Your computation of the tributary areas and axial loads on the columns due to vertical loads was really spot on, as if you used a calculator off screen. Generally, what works in my practice of sizing my foundation thickness is N/(10 - 12) where N is the number of floors suspended. In as much as the loads are governing, I usually start with a smaller thickness of , N/12 and work towards N/10 thick foundation, depending on the demand on the foundation. I don’t know why Braja M Das, computes the modulus of subgrade reaction (soil spring value) by including the foundation size. I usually would prefer to pick the soil spring value from the geotechnical report if it’s available or I simply, divide the allowable SBC/ allowable settlement. Where allowable settlement is 50mm for rafts and 25mm for isolated and combined footings per BS/EN codes. I would have to read Braja M Das’s material for more information on how the soil spring values is computed. When foundation overlap is 70% or more then a raft is required. ✅ however most client would still prefer combined footing in overlapping areas to a whole raft due to concrete and rebar cost. Great tutorial by CEE I have some technical questions for you, which I would type out shortly.

[@niisarpei3676]

Some technical questions for you Sir. I hope you address them when you start with a proper project or future tutorials. 1. For an economical foundation/raft design, is it possible to reduce the reactions on the raft/ foundations due to gravity loads by applying an imposed load reductions factors to the columns since the structure would usually not experience all floors, fully loaded with maximum live loads at the same time? I would love for you demonstrate how Robot does that. The BS 8110 recommendations is that the vertical live loads are reduced by these factors (1, 0.9, 0.8, 0.6 and 0.5), all live loads beyond the 5th floor is halfed and below the 5th floor are respectively reduced by corresponding factors. Am sure the ACI 318 and other international codes have that provision. 2. How do I query robot to know which load combination is used to size the foundation in the provided reinforcement module.? Which combination is used to design for bending and shear demand on the foundation? I have a feeling, it uses the ULS combination for all foundation designs and checks, instead of using the SLS combo for pressure checks at the base of the foundation and the sizing of the foundation. I remember we only defined ULS combinations so far and imported load cases into the reinforcement module instead of combinations. 3. I wish you had a comparative model, where the actual column sections are modeled as part of the raft and axial loads applied to the top node of the columns as point loads so as to capture the actual distribution of moment and stresses across the cross section of the columns. Just as you do, I usually don’t pick high hogging Moment, shear, deformation at the column center point but half way between the column center point and the column face of the column for concrete structures. Am not sure, but I think I saw some settings in the member design labe under tools. How can I achieve this scenario using robot? I wish you throw more light on how hogging moments is handled by robot across the column supports. 4. Could you take a deep dive into provided reinforcement for slabs in the future? Thank you Sir. Sorry if my comment is too long .

[@niisarpei3676]

I would have to try out some of the questions I have raised using Robot and see how it goes.

[@CivilEngineeringEssentials]

​@@niisarpei3676 Absolutely no problem. such comments are actually welcomed. There are provisions for LL reduction in the ACI 318 code. I have to dig them up. I would talk about those in future videos when modeling full structures. I will add this to my ToDo list. It is now updated to reflect the request there. as for 2, yes robot in the foundation module (spread footings) does show you the controlling combination. I will show it as soon as I can ^_^ as for 3, it does not really help. I have to check it myself but columns are modeled as "bars" where they transfer their loads to the raft at the node. Which would be similar to a point load. I remember there was something that allows for an area loading in robot, I have to check it out and get back to you. The comment (point 3) really intrigued me and I want to check that out in a future video. as for 4, definitely. Yes. Especially that there are some practical notes to talk about especially in terms of cut-off bars and extra reinforcement. This is a really nice topic and definitely deserves a video of its own I really like those comments, and that is why I pinned it. Such comments not only help the other viewers, but actually helps me plan my own content. So a huge thanks to your thoughts on this. 👍

[@CivilEngineeringEssentials]

Once again, a big thank you for your comment. I kind of like seeing the BS standard perspective on those topics. N/10-12 is actually not far off of my 100mm per story. As a matter of fact, the 100mm per story is exactly N/10 (10 stories / 10 = 1m, 100 x 10 = 1000mm) It draws a big smile on my face realizing this. About Braja, yeah it is kind of the "go to" reference for people studying using the american framework and codes. It is kind of a big deal there. Still, I agree. If the K factor is available from the soil report, one should absolutely use it. The 70% idea was taught to be me like 10 years ago when I was still a junior engineer. Of course you are right. Clients want to save money and are not really willing to switch to raft or mat foundations. This will put extra burden on us the designers, as we have to make sure that the force overlap below adjacent foundations does not exceed the bearing capacity of the soil. I am really happy to read your comment. I have added most of your points to my ToDo list. You can see my updated todo list when expanding the description of my latest video. Regards, CEE

[@niisarpei3676]

@@CivilEngineeringEssentials it makes me happy to be on the same page with you sir especially when it has to do with sizing members. Thank you.

[@craciunalexandru1288]

By far the best Robot Tutorials I have ever seen 👏👏

[@CivilEngineeringEssentials]

Hi there dear Engr. Thnx a lot for your kind words. It honors me to have you here. 👍

[@donaldkhanye2323]

Hello CEE. First and foremost, outstanding tutorial, thank you! You are so relaxed and yet there are tonnes of excellent tips (one after another from start to finish) on this video. You really are the G.O.A.T period. Congratulations on model #3 mimics and the ideas that this may have given you to implement on your STRADO software. I’ll say it again, these mimics and the comparative analysis that you do are a welcome bonus and are very helpful for deeper appreciation of the concepts behind the scenes. Re: 28:40. In my opinion, the 70% (or any other %) coverage “rules of thumb - ROT” should be viewed as a very rough and general ROT, never as an absolute or a requirement. For me, the available soil bearing capacity v/s structural loads and the issue of “differential settlement” which you have also touched upon in this tutorial should be amongst the focal determining factors whether to use footings or mat. Re: 04:15. Your ROT minimum of 300mm and 100mm per story is a very good starting point that is relatively easy to interpret (of course the starting thickness value is a placeholder with the actual design thickness value to be sized during the design process). Too often, most speak of raft thickness as ranging from 0.5m to 2m or even more but this is sadly quoted or stated without a clear relatable reference like yours that one can easily attach to their structure. I find your ROT as the most “straight to the point” so far. Thank you again for the wonderful tutorial. Ps: The mesh on the slab in your tutorial was made of near perfect squares (1m x 1m). The similar slab model that I made also had similar near perfect squares mesh but it also had a mix of a few irregular quadrilaterals and triangles and even X-cross in one of the internal columns load point. Is there a way to manually “clean-up” simple mesh like the above? If so, could you perhaps include how this can be done in future videos?

[@CivilEngineeringEssentials]

Well, thnx for your comment. So I am kinda the Magnus Carlsen in RSA ^_^ thnx a lot, it encourages me to improve even further. I agree on both comments about the rules of thumb mentioned in the video. Another subscriber, Nii Serpai mentioned that he is using in his BS implementation N/10-12 which is similar to my ROT. As for the request, of course. I will add it to my ToDo. Regards, CEE

[@donaldkhanye2323]

@@CivilEngineeringEssentials 😂🤣😂♟♟♟You are kinda of but with one extremely technical and significant difference, I have not (yet) seen you simply resign tournament when defeated or when you are faced with challenges of the likes of Hans Moke Niemann.

[@CivilEngineeringEssentials]

@@donaldkhanye2323 I am following that issue actually. ^_^ it is kinda the top story at the moment. Resigning from the 2nd move is kinda odd. Let's see what Gotham Chess, Hikaru Namakura and Agadmator say about this. I haven't had the time to check those out as the semester has started and I barely have time to follow all of those things ^_^ Anyways, all the best, CEE

[@DeepakPatil]

That was an amazing video...I found this video exactly at the right time.. Thankyou so much. Please make an elaborative video on wind loading using Eurocode. Just a simple video to explain interpretation of wind code. Thanks in advance.

[@CivilEngineeringEssentials]

Hello there. I am happy you liked it. Sure, I will add it to the "planned videos" that you can find in the description. Please help increase the reach of this channel by spreading it amongst your colleagues Regards, CEE

[@aakarshagrawal7200]

my man , you are doing god's work. Thank you so much.

[@CivilEngineeringEssentials]

Happy it helped. Most welcome. I wish you all the best.

[@costiqueR]

Excellent presentation, thanks a lot!

[@CivilEngineeringEssentials]

You are most welcome. Stay tuned for more content Also, if possible, suggest this channel to ur friends. Regards, CEE

[@gerasimossantos3189]

Great Video as always. One small question: If for some reason (seismic combination, etc) we have positive reactions (uplift) on raft, what that practically means? We should make a rotation check for the whole structure?

[@HR-dz5vu]

Thank you very much, I learnt a huge amount from your video. I thougjt I knew alot about Robot but was pleasantly surprised. Best wishes.

[@CivilEngineeringEssentials]

Hi Dear Haroon, thank you very much for your feedback. Help spread this channel by recommending it to your friends. Regards, CEE

[@adenipekuntunmibi6344]

Very informative. Thank you. On the 3rd model. I think if the modulus of elasticity is activated for the floor and a planar support condition (spring) is applied without the k values, it would probably give similar result.

[@CivilEngineeringEssentials]

Most welcome. The suggestion is really interesting, I think it might be the case. I have to check it in detail Anyways, welcome to the channel ^_^ Regards, CEE

[@afroass]

This was a very good tutorial thank you so much I really appreciate it!

[@CivilEngineeringEssentials]

You are most welcome. You can help the channel by suggesting it to your friends ^_^ Regards, CEE

[@przemeksmereka825]

Hi, Thank you for this tutorial. Really appreciate this! When running the analysis does ROBOT perform rotation check and sliding check of the raft foundation? Meaning that if we get a convergent result (no errors in ROBOT when calculating) its means its a safe design for rotation and sliding? Or does these calculations need to be done and verified by hand? Thank you so much for the answer in advance and like I mentioned before I really enjoy watching your videos. I dont think there is another YT channel like yours where you can explain things in such an easy way! Shared it with my engineering friends at work!

[@CivilEngineeringEssentials]

Hi there. Sorry for the late reply. Also, thank you very much for sharing the channel with your friends ^_^ RSA does not perform sliding and rotation checks on rafts. Unfortunately, you would have to do it by hand.

[@przemeksmereka825]

@@CivilEngineeringEssentials Thank you so much for the answer! Keep up the good work, i enjoy the content :)

[@calypsotravel]

Excellent video

[@CivilEngineeringEssentials]

Thmx a lot. Stay tuned for more videos. Also, please consider auggesting this channel to your friends to support it.

[@slyyck]

Very informative.

[@CivilEngineeringEssentials]

Glad it was helpful! Stay tuned for more content

[@sothattheng8624]

This is great VDO! hope you'll make the real structure with Math foundation in the future.

[@CivilEngineeringEssentials]

Hello there, I am happy you liked it. Keep up and stay tuned, I have that video idea in mind. Regards, CEE

[@sothattheng8624]

@@CivilEngineeringEssentials Thanks, I'm looking to see it.

[@user-nx3fg9zx7x]

I ve been watching your videos, and learnt a lot from them. You are one of the few that know how to use the program and structure calculations. I am desingning a mat using the k situated in the thickness panel and only a few areas surpass the maximum soil tension( a have a shear wall there). So, I wanted to consider some plastic behavior by modeling the slab with bilinear supports instead of an elastic support . I saw that robot allows you to model bilinear supports for point, linear and planar modules. I tried to model those supports with the planar interface but i am not sure which area is considered automatically by robot. I saw that you placed the soils K considering the tributary area according to your mesh size. Do you know if robot does this automatically if i model them directly as a planar support??

[@CivilEngineeringEssentials]

Yes, if you model any support: Be it elastic, bilinear or anything, what robot ends up doing, is it applies a spring (linear or even bilinear) based on the tributary area of the elements, and models the soil behavior using those springs. By the way, that is a really interesting topic, to model elasto-plastic soil behavior. Kudos to you, that is outside-the-box thinking. Just one little thing to consider: if it is clay or clayey soil, plz remember that your stress might be beyond the consolidation stresses. As you remember, this changes the behavior of clayey soils. Hope it made sense. Regards, CEE

[@TaghiRad-z9u]

It was good detailed of the mat foundation loading. Do you have design of RC mat foundation and how to detail underside concentrated loads such as columns? Thanks.

[@CivilEngineeringEssentials]

Hi there, I am really happy your liked it. So far, I haven't prepared a video about this on the channel. I think I should prepare such videos once I finish my Warehouse and RC structure series. so stay tuned for more videos, and consider supporting the channel by suggesting it to your friends. Regards, CEE

[@amiralzein9603]

Thank you about your content,and i have questions What about replce elasticity of foundation kz and you use support Mid span equal kz Edge equal half And corner Please explain this step more it's very important I and i am sorry to my alot question Thanks cce❤❤❤

[@CivilEngineeringEssentials]

Hi there, Happy for your comment. Feel free to ask anything anytime. When I replaced the elastic foundation with my own spring supports, I had to find the spring support stiffness. Now elastic foundation stiffness is as follows: F = N/m2 x = m Kz = N/m2 / m In a spring support, the Ks-factor is simply N/m So to get the equivalent spring factor Ks from Kz, I have to multiply by the tributary area. No on edges, it is obviously smaller than in the middle. Also, note that it was easy for me to predict the area because the mesh was quite organized. I cannot do the same when the mesh is distorted. Finally, the reason I did this calculation is to show "how robot thinks". Regards, CEE

[@amiralzein9603]

@@CivilEngineeringEssentials Thank for you🌹🌹🌹🌹🌹

[@yasarameer9255]

Great and informative tutorial ...... I think that the command (reduction of forces above columns and walls ) in (Results -> Maps -> parameters ) works to reduce the moments and reactions concentrated under and above walls and columns ..... can you give it a try and make a tutorial on it

[@CivilEngineeringEssentials]

Hi there, First, thnx a lot for your comment, it means the world to me when my videos spark discussions and comments. The suggestion is really good! I will definitely try prepare a video about it explaining the "behind the scenes" details of such commands. However, I might need some time because I am currently doing an RC design series that I want to conclude. But once again, GREAT suggestion and a huge thnx to you. Regards, CEE

[@Mr.SKA-w4h]

Hi there , when will you do the design of a raft foundation ? i have searched all your videos for the design of such foundations, but i didn't find . especially the foundation of the concrete (2 blocks connected with a bridge) tower building that you modelled in the 18 video series. there is no design for raft. thanks ,

[@CivilEngineeringEssentials]

Yep, seen your other comment. A video on a Raft + a video on pool walls + dynamics series are definitely on my radar. I just need to find time to filming those ^_^ Stay tuned for more content. Regards, CEE

[@PATHMINDER]

In minute 8:04 100 KPa was in box of (estimated foundation load). So, Did you calculate it based on your loads and mat area ,or it was existed by Default?

[@LodyBasha]

شكرا ياخي جزاك الله خير فديو ممتع ، هل عملت فديو لتصميم الرافت ؟ بحثت في قناتك ومالقيت

[@CivilEngineeringEssentials]

ما ظنيت، أعتقد الفيديو الوحيد الموجود هو التحليل، ممكن أضيفلي واحد للتصميم أول ما يصير عندي متسع من الوقت، يعطيك ألف عافية.

[@kaiganaxabystc4136]

Great!

[@CivilEngineeringEssentials]

Thnx a lot 🌹 Stay tuned for more content.

[@KassemDeeb90]

Hello.. Thank you first for your effort.. Just a question, I saw that you compared the obtained settlement to 2.5cm. the definition of Kz is the ultimate soil pressure (allowable times the safety factor) divided the 0.025m settlement, so it is not enough to compare the settlement of the foundation to 2.5cm, because we should compare the obtained value to the third of 2.5cm to ensure that soil pressure obtained by FE is less than the allowable pressure and not the ultimate one. I'd like to know what you think.. thanks again for your effort

[@CivilEngineeringEssentials]

Yes, you are 100% correct if the Kz used is based on ultimate. If it is based on allowable then all is good. It slipped my mind. I should have mentioned it in the video, so a huge thnx for your comment. Let me rephrase this for the interested readers: Dr. Kassem says: - Let us assume that the max allowable settlement is 0.025m. - Also, let us assume that the Kz used in the software is calculated without factor of safety. - The "simplistic equation" is: delta = F/K. Since the K is without a factor of safety, there are two approaches for this: Approach 1: calculate the "safe" "allowable" K by dividing by 3 (Factor of Safety). Then use it calculate the the settlement. (So we would need another model for this) Approach 2: realize that the soil is "too strong" and limit the deflection to 1/3 of the 0.025. I hope I was able to get your point correctly, Dr. Kassem. Amazing point! Thanks again for your efforts. Please tell me if I was able to address your point. (I will also add this discussion to the video description. Thank you very much) Regards, CEE

[@KassemDeeb90]

Thank you for your effort, indeed this is my daughter Fatima that do her KZbin channel using my email :), any way , I am Kassem Deeb, his father and the civil engineer. Thank you again and again for your useful videos@@CivilEngineeringEssentials

[@aliomar6441]

Very happy to have my professor, Kassem Deeb, meet my favorite KZbinr, DC CEE.

[@CivilEngineeringEssentials]

Most welcome I modified my comment 🌹 It honors me to have you here Prof kassem Feel free to start any discussions you want. I am more than happy to engage 👍

[@issouabdou239]

I want to become your student

[@CivilEngineeringEssentials]

Thnx for your comment. Well, stay tuned to this channel and you will get more lectures