How to model a concealed beam in ETABS & How to design the Hidden Beam
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- Опубліковано 1 гру 2021
- Concealed beam is a myth. Before even discussing how to model a concealed beam or thinking about a concealed beam design, know this fact that there is nothing called concealed beam.
Why I say this about the so-called concealed beam?
A hidden concealed beam shall be only used as a tie for columns so that the slenderness of the column can be reduced and also its sway can be controlled.
You can also adopt a concealed beam when there is a concentrated load or a line load from a wall on a slab. This hidden concealed beam will help to reduce the intensity of the line load on the slab. The beam needs to be hidden if architecturally we cannot provide a beam there.
Basically, a concealed beam is a part of the slab as it is only as thick as the slab and is not stiff enough to behave as a beam and take the load from the slab.
You will have to design the slab as a single panel with out considering it separate at the concealed beam location.
If you design the slab as separate panels, there can be cracks or even failure of the slab depending up on the redistribution ability of the slab and also on the margin on load considerations and factor of safety adopted
Now how do you do the concealed beam design?
You don’t have to even design it as a beam. It is not taking any gravity load from the slab. If you design the slab that’s adequate.
In case you have provided the hidden beam in slab as a tie to columns, it will attract a tie force - Basically a tension and compression when the column sways. The slab itself is stiff, only that there are no continuous bars in it. So, this concealed beam strip will help if there are continuous rebars in it to take the column tie forces.
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Such useful information provided by you. Thank you
Thank you 🙂
Thanks sir, very useful.
Nice to know you liked it
Great video. I have one question. Why didn't you model the slab into two parts. Like one slab on left of concealed beam and 2nd slab on right of concealed beam? Maybe then bending moments would have showed up?
Thanks for the comment. And happy that you learnt from it. However why do you think I will overlook such a simple point ? :-)
I will leave that exercise to you to split it and check the moments :-)
Or let me tell you :-)) - In ETABS it does not matter if you merge or split the slab as long as it is a shell. Shells would behave as it should inspite of split or merge.
If it is a membrane it is a different thing though. Check it yourself :-)
Splitting the slab means again we have to consider that Concealed beam as Normal roof beam.
@@saimanish7879 No it dont mean that. I request you to do these and find out for your good :-)
Me saying is easy but if you do you experience it. If your split or merge, shell will behave the same way.
Thank for the video.
How to design this beam,i mean how much reinforcement is needed.
For the gravity loads, you dont have to. It is like a dummy beam used to distribute the line load on top of it coming from a wall. It is a part of the slab and you are desigining the slab as a shell for the forces coming at the location. Additional rebars if any as a through rebar is provided for either tie action or to redistribute the line load from any wall there as an additional preacaution. You can interpret the shell results and design the slab
Thank you Sir...,🙏
Most welcome
1. I am not sure if we need to add a tie beam at a column to retrain it. I never saw a flat slab column needing a beam to tie it.
2. Even if we add that beam, for that beam to qualify as a support it must satisfy stiffness requirement per ACI 8.10.2.7. Otherwise how we will define at point that beam will start acting as support?
Shashank thanks for the comment.
1) The core topic of the video is about concealed beam that people misuse. The intention was to educate beginners not to do the mistake beginners do which is mentioned in the video. Please dont selectively choose and twist what I have mentioned. Where have I mentioned about Flat slabs and the column needing a tie in flat slab. Any flat slab structure will need a separate seismic resistance mechanism like a single system or by using the edge beams to form a structural resistance sytem. Thats a separate topic. I suggest you make a video on that and post in your channel and I will comment my opinion seeing yours.
I was refering to a normal building system where columns are untied, it is better to tie it for better tie action.
2) I am aware of the tie action needed and I have quickly mentioned about the compressive and tensile capacity needed for the concealed beam to act as a tie for the column. As mentioned above, the topic of the video was not tie action. I never ever in the video mentioned about the concealed beam acting as a support. I mentioned it acting as a tie for the column for the lateral load cases. The slab as such is immensely stiff and can perform this role provided the salab is well connected to the column. Even if we do that, the slab offer compressive action. what about tensile? thats the reason continuous rebars are prefered at that location as a tie. Now that people call it concealed beam and my point was to treat that as just a tie and not a beam.
@@CIVILERABangalore Dear Sir, any apologies if my tone seemed too critical. That's not my intention. I appreciate you taking time to explain fundamental concepts to the young engineers, which is very much needed, especially people with vast experience like yourselves.
1. I haven't designed any normal slabs other than flat slabs. So this is the first time I am seeing "tie beam" concept and I am not able fully understand/appreciate the need for it. Hence my question.
2. I understand the you are trying to conclude not to mis-understand tie to be a beam and design slab by cutting its span at the tie beam. What it means is some young engineer trying to use beam as support and splitting the slab by discontinuing the rebar at the tie beam. Which can be done provided the beam is deep enough to have sufficient stiffness per above mentioned ACI clause.
Let me know if I am getting anything wrong here.
If you think my comment is misleading/too critical, I can remove it.
@@shashankm1403 Your misunderstanding led to criticism may be. I dont mind criticism by the way🙂 . However please see the video again and ensure you understand what I mean.
@@shashankm1403 Yes when the beam has stiffness , it is a proper beam. The video is talking about the so called ''concealed beam''
I am ok with people criticising 🙂. However your above statements were not on the core topic of the video and out of your confusion on the tie. I suggest you model a structure with out beams tieng the columns with a 100mm slab thickness (slab modelled as shells) and check the stresses in slabs and also the lateral deflections and the column design. Compare this after providing beams.
Can we provide this concealed beam below brickwork on slab? Or avoid it?
As mentioned in the video, yes. but it wont be taking the entire load of the wall like a beam. It only will help in distributing it a bit.
@@CIVILERABangalore Thanks sir
@@shashankkumar8086 my pleasure :-)
Hello sir, can we avoid to model concealed beam?
You dont have to model it. With respect to effective length of column, you should modify its unsupported length while designing
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