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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3835
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Posted: Tue Oct 09, 2012 12:13 pm Post subject: Teng's curve |
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Dear Er Sukanta Adhikari ji
Yes , you are very right in pointing out that Type of structure is very important
while allowing loss of some % contact of footing .
I think , in normal structures it can be easily allowed but for structures where
functionality is impaired , this may not be permitted. Supporting structures
of sophisticated defense gadgets, sensors, Radar antena and communications
structures are sensitive to deflections . Though in such cases strict deflection limit is
also imposed on structure , but alongside foundations must not lose contact .
Even if structure is adequate against stringent deflection limit, upliftment
of foundation part(loss of contact) will deviate the requirement .
best regds
vikramjeet
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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5538 Location: Gaithersburg, MD, U.S.A.
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Posted: Tue Oct 09, 2012 6:45 pm Post subject: Re: Teng's curve |
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Dear Er Adhikari,
For any structure, the value of e should not exceed L/6 or B/6- see Fig. 6.14 of Teng's book. (pp.130-135). In EQ zones no tension should be allowed in soil.
Regards,
NS
vikram.jeet wrote: | Dear Er Sukanta Adhikari ji
Yes , you are very right in pointing out that Type of structure is very important
while allowing loss of some % contact of footing .
I think , in normal structures it can be easily allowed but for structures where
functionality is impaired , this may not be permitted. Supporting structures
of sophisticated defense gadgets, sensors, Radar antena and communications
structures are sensitive to deflections . Though in such cases strict deflection limit is
also imposed on structure , but alongside foundations must not lose contact .
Even if structure is adequate against stringent deflection limit, upliftment
of foundation part(loss of contact) will deviate the requirement .
best regds
vikramjeet
.
--
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sukanta.adhikari General Sponsor
Joined: 26 Jan 2003 Posts: 726
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Posted: Wed Oct 10, 2012 4:46 am Post subject: Re: Teng's curve |
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Respected NS,
If e value does not exceeds L/6 or B/6 ..its means no tension is developed below footing....then what is the use of Tengs chart...Tengs chart as from the discussion says...that it may be used when the footing is subjected to biaxial bending and the footing has loss of contact with the soil.
And regarding EQ zones as mentioned you that no tension is to be allowed is different from IRC provision mentioned by Vikramjeet sir.
Regards,
S Adhikari
Dr. N. Subramanian wrote: | Dear Er Adhikari,
For any structure, the value of e should not exceed L/6 or B/6- see Fig. 6.14 of Teng's book. (pp.130-135). In EQ zones no tension should be allowed in soil.
Regards,
NS
vikram.jeet wrote: | Dear Er Sukanta Adhikari ji
Yes , you are very right in pointing out that Type of structure is very important
while allowing loss of some % contact of footing .
I think , in normal structures it can be easily allowed but for structures where
functionality is impaired , this may not be permitted. Supporting structures
of sophisticated defense gadgets, sensors, Radar antena and communications
structures are sensitive to deflections . Though in such cases strict deflection limit is
also imposed on structure , but alongside foundations must not lose contact .
Even if structure is adequate against stringent deflection limit, upliftment
of foundation part(loss of contact) will deviate the requirement .
best regds
vikramjeet
.
--
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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5538 Location: Gaithersburg, MD, U.S.A.
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Posted: Thu Oct 11, 2012 10:27 pm Post subject: Re: Teng's curve |
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sukanta.adhikari wrote: | Respected NS,
If e value does not exceeds L/6 or B/6 ..its means no tension is developed below footing....then what is the use of Tengs chart...Tengs chart as from the discussion says...that it may be used when the footing is subjected to biaxial bending and the footing has loss of contact with the soil.
And regarding EQ zones as mentioned you that no tension is to be allowed is different from IRC provision mentioned by Vikramjeet sir.
Regards,
S Adhikari
Dear Er Adhikari,
Yes. You are right. They are the limits for not having negative pressure in soil. Is it not better not to have negative pressure in soil when the structure is subjected to EQ?
When I have time I will go through the IRC provisions metioned by Er
Vikaramjeet.
Warm regards,
Subramanian
Dr. N. Subramanian wrote: | Dear Er Adhikari,
For any structure, the value of e should not exceed L/6 or B/6- see Fig. 6.14 of Teng's book. (pp.130-135). In EQ zones no tension should be allowed in soil.
Regards,
NS
vikram.jeet wrote: | Dear Er Sukanta Adhikari ji
Yes , you are very right in pointing out that Type of structure is very important
while allowing loss of some % contact of footing .
I think , in normal structures it can be easily allowed but for structures where
functionality is impaired , this may not be permitted. Supporting structures
of sophisticated defense gadgets, sensors, Radar antena and communications
structures are sensitive to deflections . Though in such cases strict deflection limit is
also imposed on structure , but alongside foundations must not lose contact .
Even if structure is adequate against stringent deflection limit, upliftment
of foundation part(loss of contact) will deviate the requirement .
best regds
vikramjeet
.
--
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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5538 Location: Gaithersburg, MD, U.S.A.
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Posted: Tue Jun 03, 2014 4:14 pm Post subject: Re: Teng's curve |
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Dear All,
An excellent paper has been published by Er Bijay Sarkar in the June 2014 issue of ICJ. I am enclosing it for your reference.
Best wishes,
NS
[quote="Dr. N. Subramanian"] sukanta.adhikari wrote: | Respected NS,
If e value does not exceeds L/6 or B/6 ..its means no tension is developed below footing....then what is the use of Tengs chart...Tengs chart as from the discussion says...that it may be used when the footing is subjected to biaxial bending and the footing has loss of contact with the soil.
And regarding EQ zones as mentioned you that no tension is to be allowed is different from IRC provision mentioned by Vikramjeet sir.
Regards,
S Adhikari
Dear Er Adhikari,
Yes. You are right. They are the limits for not having negative pressure in soil. Is it not better not to have negative pressure in soil when the structure is subjected to EQ?
When I have time I will go through the IRC provisions mentioned by Er
Vikaramjeet.
Warm regards,
Subramanian
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bijay sarkar ...
Joined: 14 Dec 2009 Posts: 314
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Posted: Sat Jun 07, 2014 11:11 am Post subject: |
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Dear NS Sir, You are always encouraging to all of us. I myself and I think, many others here, get enormous energy from your continuous presence & guidance here. The enclosed paper, is also a product of the encouragement, I got from all SEFI members.
Thanking you,
With Regards,
Bijay Sarkar
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3PlankWalker SEFI Member
Joined: 31 Jul 2014 Posts: 3
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Posted: Wed Oct 29, 2014 12:38 pm Post subject: |
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Dear Mr Bijay Sarkar,
The paper is really helpful.
I am trying to replicate the Fig 5 from the paper.Here is what I have so far.
Sir, how do we generate Kmax Curve for a specific Kmax Value .
Thanks
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bijay sarkar ...
Joined: 14 Dec 2009 Posts: 314
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Posted: Thu Oct 30, 2014 10:22 am Post subject: |
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Dear Mr 3PlankWalker,
From your question, it appears to me that you have entered deep into the solution and near to the end. I am trying to give you the reply as follows :
1. Assign the pressure values in an array for which you want to generate curves.
Pressure(1) = 2: Pressure(2) = 2.5: Pressure(3) = 3: Pressure(4) = 4: Pressure(5) = 5 ; Pressure(6) = 6: Pressure(7) = 7 ; Pressure( = 8 ; Pressure(9) = 10 ; Pressure(10) = 12
Pressure(11) = 14 ; Pressure(12) = 18 ; Pressure(13) = 20 ; Pressure(14) = 25 ; Pressure(15) = 37 ; Pressure(16) = 49
2. For x = 0.00000001 To 2 Step 0.05
If x <1> 1 Then
Y1 = x - 1: Y2 = 2
End If
Y2Keeper = Y2
For j = 1 To 1000 Step 1
y = (Y1 + Y2) / 2
If y = Y2Keeper Then
Exit For
End If
If Y1 = Y2 Then
Exit For
End If
3. Find out the Neutral Axis case no.
4. Corresponding to the NA case no, Find out Eb/B, El/L and maximum pressure co-efficient corresponding to above x & y
5. Compare the calculated pressure value and curve's pressure value and accordingly change the values of Y1 & Y2, if needed, as follows :
6. if maxpressK < Pressure (i) Y1 = y....else Y2=y
7. if maxpressK = PressureK(i) Then Writedown the values of El/L, Eb/B and corresponding pressure in file.
8. Consider next value of x and repeat the above again.
9. Collect all the El/L, Eb/B and pressure values in a sheet.
10. Then generate the curve from the data file.
Hope now you will be able to generate the code for Kmax curve for a specific Kmax value.
regards,
bijay sarkar
Last edited by bijay sarkar on Thu Oct 30, 2014 10:53 am; edited 3 times in total |
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3PlankWalker SEFI Member
Joined: 31 Jul 2014 Posts: 3
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Posted: Thu Oct 30, 2014 10:32 am Post subject: |
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Dear Sir,
Thanks for the reply. Will go through the solution.
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rex_alfred SEFI Member
Joined: 17 May 2018 Posts: 3
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Posted: Wed Jan 01, 2020 11:02 am Post subject: Teng's curve |
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Dear All,
Thanks for the detailed discussion on base pressure calculation of footings subjected to biaxial moments.
In the search for a good paper for implementation of linear soil pressure method with redistributed base pressure, i came across few interesting papers.
1. Determination of Base Stresses in Rectangular Footings under Biaxial Bending - Günay ÖZMEN
2. Analysis of Eccentrically Loaded Rectangular Footing Resting on Soil A Numerical Approach - Jignesh V Chokshi
3. Analysis of isolated footing subjected to axial load and high biaxial moments and numerical approach for its solution - Bijay Sarkar
These papers have already been extensively discussed in this thread.
I would like to add one more paper discussing the same subject through a different methodology derived from basic concepts.
4. New Iterative method to Calculate Base Stress of Footings under Biaxial Bending - Ibrahim Aydogdu
In my opinion, the method discussed by Aydogdu is by far the simplest to implement on computer.
The stress equation considering that all points of footing are at compression.
Stress equation = F/BL + Mz/Iz*x + Mx/Ix*z
This stress equation becomes the equation of Neutral Axis (NA) plane when stress is zero.
The paper alters this stress equation by adding coefficients a, b, c for stress due to axial load, moment about z axis and moment about x axis respectively.
Stress equation = a*F/BL + b*Mz/Iz*x + c*Mx/Ix*z
The iteration starts with a=1, b=1,c=1, and intersection points of NA with footing edges are calculated if there is tension in the footing.
The force is calculated by double integration of stress equation.
The moments are calculated by multiplying the forces with the corresponding lever arms.
At the end of every iteration the calculated resistance by soil (F*, Mx*, Mz*) are compared to the loads (F, Mx, Mz) applied. If the difference between resistance and force are within allowable limits. The plane formed by the assumed a, b, c is the actual NA plane. Else the iterations are continued by altering a, b, c and thus changing the position and orientation of NA plane.
This method is independent of the shape of the contact area of footing.
I felt like updating the thread with this nice paper published in 2016.
Hope it is useful for the community.
Wish you all a very happy year 2020.
Regards,
Rex Alfred
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