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[bablu]

Sir,
         I need help for footing design where my edge columns are positioned 2' from property line. I am willing to design it as isolated footing with pedestal to counter eccentricity.

[vikram.jeet]

Eccentric Footing :-

Please tie it with inner column at footing level itself ,, AS STRAP BEAM .

ECCENTRICITY ON FOOTING IS NOT COUNTERED BY PROVIDING PEDESTAL.

ALSO REFER EARLIER DETAILED DISCUSSION ON THIS TOPIC

[bablu]

[vikram.jeet]

Dear Er,,
In my opinion eccentricity of system is never lost by providing pedestals,, pedestals have their own other advantages.

However in yr case footing have clear overhang from property line and pl calculate eccentricity of column/s wrt centerline footing and work out moment on footing,
Calculate maximum and minimum base  pressures using :-
P/A plus / minus M/Z
If minimum base pressure is + ve,, then design footing.
But if bade pr show negative value,  then carry out redistribution of base pressure as follows :-
e= M/P
P is the total column load plus soil wt over footing.
Contact length of base pressure = X= 3(L/2 - e)
L is the ftg dimension along eccentric moment

This contact Length must be about 80 percent for morning mal case and 67% under seismic.

ALSO CHECK MAXIMUM BASE PR= 2*P/(B*X) ,  this must be less tha GROSS SBC  ( SINCE DOIL WT IS ALSO TAKEN IN VERTICAL LOAD P) .

If it contact length X is less tha 80percent/67 percent (EQ) , then TIE EDGE COLUMNS WITH INNER COLUMNS USING TIE BEAM CALLED STRAP BEAM.
STRAP B EAM CSN BE DESIGNED FOR FULL Eccentric MOMENT ON FOOTING , , For more exact calculations, refer standard st design Text book.

It is advisable to have more length of footing parallel to property line and lesses width slong eccentric dir to reduce eccentricity on footing center line.

Reinforcement of strap beam, in this case will be predominantly on top for eccentric moment countering.

Pl note :- That values of contact length 80 percent Normal case / 67 percent under EQ ,, we're given in IRC 78 on Rocky strata for bridges,, NBC is silent ,  hence these figures are suggested,  but check back from yr proof consultantvwheather they allow.