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Design Corner Eccentric Footing on Both Side
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kiranklk
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PostPosted: Tue Mar 01, 2011 6:27 am    Post subject: Design Corner Eccentric Footing on Both Side Reply with quote

Hi Please Anybody Tell Me How to Design Corner EccentricFooting on Both Side Without Starp Beam. And Please Suggest me Any Books ForReference and Excel Spread Sheets.


Regards Kiran.
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B.V.Harsoda
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PostPosted: Tue Mar 01, 2011 8:05 am    Post subject: Reply with quote

Refer Links:-

http://www.sefindia.org/forum/search.htm?cx=011309042287105965323%3A-rusg9dz88q&ie=UTF-8&q=shoe+footing&cof=FORID%3A11&siteurl=www.sefindia.org%2F#857


http://www.sefindia.org/forum/search.htm?cx=011309042287105965323%3A-rusg9dz88q&ie=UTF-8&q=l+footing&cof=FORID%3A11&siteurl=www.sefindia.org%2F#870
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B.V.Harsoda
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PostPosted: Tue Mar 01, 2011 8:15 am    Post subject: Reply with quote

Useful Spreadsheets Link:-


http://www.engineering-international.com/
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Dr. N. Subramanian
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PostPosted: Tue Mar 01, 2011 2:42 pm    Post subject: Re: Design Corner Eccentric Footing on Both Side Reply with quote

Dear Er Kiran,

It is very difficult to provide ecc. footings with out connecting it to adjacent footing with strap beams, unless it is having very low AF. When it has ecc. on both axes, it is not advisable to attempt such a footing, because footing is very important to any structure, and the loss of footing due to loss of contact may be catastrophic to any building. That is the reason why it is not included in any book. For both side ecc. footing, I suggest you to combine other footings and provide a raft, as we do in lift wells.

Best wishes
NS

kiranklk wrote:
Hi Please Anybody Tell Me How to Design Corner EccentricFooting on Both Side Without Starp Beam. And Please Suggest me Any Books ForReference and Excel Spread Sheets.


Regards Kiran.
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B.V.Harsoda
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PostPosted: Tue Mar 01, 2011 4:27 pm    Post subject: Reply with quote

In previous posting Er. Vikramjeet has been Explained nicety as Below:-


"L- Footings  is generally required to be provided at the edge of
property line. This footing, if not connected to internal column, is
subjected to very high  moment due to eccentricity  of load  w r t
footing centreline.
It is always preferable to connect this footing with some
internal column through a strap beam so that moment
due to eccentricity is taken care by this beam.For economy
in strap beam, it is necessary to take footing dimension
in direction of eccentricity,as less as possible,say, half the other.

"For edge footing without strap beam,it is difficult to satisfy
the no upliftment condition as redistribution is not permitted
for footings resting on soils.Even if some redistribution is
taken it may give very high value of upliftment of footing
and max pressure after redistribution is quite high(it has to be
less than SBC)
Some designers take advantage
of passive soil resistance(with some  FOS) offered by the edge wall
to relieve eccentric  moment but in that case edge wall shall
be strong enough to withstand this passive relief moment.

Long back I had seen a paper  written by structural expert and author
Sh UH Varyani on the analysis of edge footing w/o strap
beams. This might be available in some of his books
."



In Second Post said that

"in my opinion ,try to provide strap beam as  per situation
given below in view of L-footing already cast without
strap beam.

i)assuming that  columns are not cast above top of footing

In this situation you can provide the strap beam
connecting this column to internal column at
top of footing level .

ii)assuming that  columns are  cast above top of footing
upto GL/PL
In this situation you can provide the strap beam(tie beam)
connecting this column to internal column at
GL/PL but edge column reinf provided shall be adequate
enough to transfer the eccentric moment  upto
strap / tie beam level. You can take advantage of
passive relief from soil(with some FOS) on edge wall on
either side of column .Also the orthogonal cross wall (if it exists)
will help. ( by way of its triangular load component beyond
footing line  through dispersion which will provide counter
eccentricity)"






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vikram.jeet
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PostPosted: Wed Mar 02, 2011 5:24 am    Post subject: Design Corner Eccentric Footing on Both Side Reply with quote

Corner Footing

As suggested by eminent members, the corner footing must have  
balancing strap beams in both directions to counter the eccentric
moments .These beams must be provided at footing level itself.

Avoidance of strap beam:(costly option)

A] If plinth beams are provided tie-ing the columns in
both directions

(i) The column section of corner column below plinth level shall be
increased appreciably to take care of additional bi-axial moment s
due to eccentricities in both directions. Column Reinf shall be  
worked out accordingly.

(ii) Plinth beam in each direction shall be designed for addtional
tensile force =M/Df
M = P*e
e = eccenricity= distance between CL footing and CL column
Df = fondation depth upto plinth level

This tensile force in plinth beam must have a counter force form other side
corner column, otherwise inner columns must share it.

(iii) Column above plinth beam level can have normal reinforcement

B] If plinth beams are NOT provided and roof beams are
available at roof level (i.e next floor level)

(i) The column section of corner column below roof level shall be
increased suitably to take care of additional bi-axial moment s
due to eccentricities in both directions.Column Reinf shall be  
worked out accordingly.

(ii) Roof beam in each direction shall be designed for addtional
tensile force =M/(Df +H)
M = P*e
e = eccenricity= distance between CL footing and CL column
Df = fondation depth upto plinth level
H= roof height above Plinth level
This tensile force in roof beam must have a counter force form other side
corner column, otherwise inner columns must share it.

(iii) Column reinf above plinth beam level can can be slightly reduced
since addtional moment (due to eccentric) varies upto roof level.

Other reductions in eccentric moments

(i) Passive less active relief from soil on side faces


Best wishes and regds

vikramjeet




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B.V.Harsoda
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PostPosted: Wed Mar 02, 2011 8:01 am    Post subject: Reply with quote

Thank you Very much Er. Vikramjeet ji, Your Knowledge ia appreciable. As rightly said by  Dr. NS Sir,due to certain reasons such footings not included in any book ,but considering cost of land & requirement of client, it is not avoidable at all times. In such situations we have to do some thing. It wiil be great work if we can be helpfull in this subject to needful structural Engineers. In past we have discussed several times.Now I request to Er. Vikramjeet ji to submit, Article Regarding L-footing & Corner Eccentric footings in Forum.

Thanks
&
Best Wishes,

B. V. Harsoda    
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vikram.jeet
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PostPosted: Wed Mar 02, 2011 9:40 am    Post subject: Design Corner Eccentric Footing on Both Side Reply with quote

Thank you, respected Harsoda sahab.

As informed by you , lot of discussion in this regard has been taken place on sefi.
These footings are not very un -common . IS codes do not provide any guidelines
in this regard .
Books on design/analysis do talk about provision of strap beams and their analysis.
However provision of these footings without strap beams is dealt seldom.The
analysis of L- footings is ,I think,dealt by our respected UH Varyani sahab in his book  
on MS buildings which is part of his Paper in ICJ.

I have posted my recent views on L -footings without strap beams purely based  
on basics.The basic idea is that eccentricity moment on footing need to be  
resisted through either a strap beam (if present) /or through column itself being
tied at certain level above.

As suggested , I would be glad to write on sefi at some future date after noting
the comments of members.

with kind regards

vikramjeet


Thank you Very much Er. Vikramjeet ji, Your Knowledge ia appreciable. As rightly said by Dr. NS Sir,due to certain reasons such footings not included in any book ,but considering cost of land & requirement of client, it is not avoidable at all times. In such situations we have to do some thing. It wiil be great work if we can be helpfull in this subject to needful structural Engineers. In past we have discussed several times.Now I request to Er. Vikramjeet ji to submit, Article Regarding L-footing & Corner Eccentric footings in Forum.

Thanks
&
Best Wishes,

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binaya shahi
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PostPosted: Wed Mar 30, 2016 1:22 pm    Post subject: width of strap beam. Reply with quote

One of my friends told me that the width of strap footing must be greater than the column without referring to any code or book or reasoning. I want to ask if its true coz I don't think it must be true. I have designed a strap beam of 9 inch width and 22 inch depth to connect two columns of dimensions 12"x12". Isn't my 9 inch wide strap beam allowed for 12 inch wide column?
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es_jayakumar
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PostPosted: Fri Dec 13, 2019 3:32 am    Post subject: Reply with quote

Dear SEFIans,

Please comment on the rationality of the design of a corner column isolated-footing attached here, that had appeared in this forum at sometime. I was not convinced with the principle / logic of this design.

E S Jayakumar



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