ฝัง
- เผยแพร่เมื่อ 16 ต.ค. 2024
- Isolated footings are sized considering the SBC of soil. What we do is ensure that the pressure due to load is less than safe bearing capacity of the soil. If this is ensured, then the isolated footing will float on the soil and will not sink or settle down. If the area of footing is not adequate then the footing will settle. And if the area is adequate then the footing will remain in place and distribute the load from columns to soil. The footing will bend in this process and forces are developed as explained in this structural tutorial on foundation.
The footing is like a cantilever
The soil pressure is from the bottom and therefore it is like an inverted cantilever
This means that the reinforcement needed is at the bottom.
However, there is a reason that we also need a min reinforcement at top if the total thickness of the footing is more than 1m.
1m thickness or more is like a mass concrete and there are chances of cracking.
We cannot afford cracks in the foundation as the footing can come in contact with water and chemicals since it is embedded in soil.
Due to the above reason, it is recommended to have a minimum top rebar too in either direction if the thickness of isolated footing is more than 1000mm.
This is a discussion going on in civilera forum and you can see the structural design video here and head to civilera forum to see the latest structural discussions.
Please like my structural video here and also like the channel.
Please spread a word about civilera Bangalore channel
You can join our groups too by going to civilera website and filling up the contact form
There is also a free course on stability and a lot more blog that you can learn from.
Fantastic
thanks
great to know you liked it
THANK YOU
Nice Video. I just wanted to ask, when you mean reinforcement at Top is usually required for depth 1000mm, I'm assuming you mean embedment depth or just the member thickness of 1000mm? Or both scenarios?
Total thickness of section
Most useful videos sir ..please I am requesting to make a more videos on 1.Structural concepts.
2 .E tab with a different floor plans.
3.how to release the moment in e tab and how to apply in practical.
4. Please make a videos on Membrane and shell thin and shell thick ..
It helps to lot off students...please sir...
Thanks for your comments.
What you asked for is quite a lot. Will consider some based on my time and content plans
However all of these are available in civilera courses and you can find it in www.civilera.com
Great and clear presentation. However, if you have 5 bars per meter, the bar s[acing will be (1000/5= 200 mm). Within 1 m, we need to have the area of 360 mm2 ( or 5x78 = 390 mm2). This is only possible if you provide H10 @ 200mm c/c.
1) 200 or 250 does not matter with respect to the topic of discussion. Discussion is about the need of top bars. is it not ?
2) 5 bars means 4 spacings. you can sketch and see yourself. 4 spacings in 1000mm is 250mm
Cheers 🙂
@@CIVILERABangalore Thanks for reply. I shall send you email.
Nice information. But you didn't explain why minimum reinforcement is provided at the top. Yes, it is in the code but what is the function of the top rebars? And why top rebars are not required for sections of thickness
It is understood. When the section is thicker, chances of cracking are more. IS has decided it for over 1m. Same is different for BS. You can check the crack width calculations in these codes
While working in a construction company, I came across a isolated column footings with depth 2.25 feet and the size of the footing was (7.5' × 7.5') and the structural drawing had mentioned top reinforcement in both directions and provided with 4 steps to hold those top bars in position . Is there any reason for it?
The info you provided is not adequate to conclude with an answer :-)
Good
Hi there is top reinforcement needed for a 600x600x500 deep footing with a 1700hx 470x470 core filled brick column?
For an isolated/pad foundation, force point of view, if the loads are uniform like what you mentioned, there is no need of rebars at the top face. However based on the code of practice in your country, there will be a min steel specification. Please see that.
As per IS codes, you will not need it as mentioned in the video.
Can anyone please provide me with an example of safe where it is possible to create isolated footing without a top reinforcement......!??!! Small large size doesn't matter just create one isolated footing in safe where top reinforcement is not required.......!!!
Generally Top rebars are not needed in Isolated footing if it is designed as a singly reinforced section. It is advisable to design as a singly reinforced section. So if you do that, the only need of top rebar in isolated footing is when the depth is more than 1000mm as per IS 456.
@@CIVILERABangalore i am using less than 1000 mm depth, even when forces is low..... there is no way where i can get zero reinforcement in top (with design strip or in FEM method) while checking for reinforcement after design in SAFE......here i am not talking about manual design....
@@vasubhadania Am sorry. I cannot understand you. 1000mm bars your won't get any where. I meant the depth.
Manual or software, you don't need top rebars unless it is doubly reinforced due to lack of adequate depth
@@CIVILERABangalore sorry i actually ment 1000 mm depth.....i am trying safe because safe can also be used for combined footing.....
While using safe there will always be top reinfo.... I want to resolve that....
In short i am trying to get no top reinforcement in safe but why is there always top reinforcement.....i want to know that reason..!!!
@@vasubhadania You are perhaps over using SAFE. You just analyse and zone the forces and dont use the design oprion