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[ramu_se]

Dear All,

Can we design the eccentric footing for the attached plan as per the attached calculation?

Kindly guide me on this.

Thanks & Regards,
Ramu.

[vikram.jeet]

Eccentric footing on boundary edge :

Dear Er -

First and foremost task in sbove footing is working out base pressure correctly.

You have taken uniform base pr,, You can do so in case you tie this column to some opposite interior column by a beam called Strap beam .

You may see for yourself that bade pressre Max will exceed many times, if Strap beam is not provided

But in this case : Pl see Max base pr as under -
P  = Column vertical load
B = Footing size in ecc direction
L = footing size in ortho dir
d  = col dim in ecc dir

Since yr col load is at edge of footing,  there is eccentricity of load wrt to footing centrline.
e = (B/2  - d/2)
Moment on footing = P * e

Footing will lift and max base pr will be very very high

Please refer sny text book for design calcs

Some relief in moment on footing due to above ecc is provided by passive soil resistance thru edge wall,, but is not much compared to ecc moment.

[vikram.jeet]

You can refer earlier detailed discussions on Edge footings in topic " Some general view '

[ramu_se]

Thank you Sir.

Kindly share if you have any references to designing the eccentric footing with a strap beam.

For example,

Edge Footing

Load on column - 300 kN

SBC - 200 kN/Sqm

Column size - 200 x 450 mm

Attached is the image for your reference.

Thanks & Regards,
Ramu.

[vikram.jeet]

Et Ramu,,

By connecting edge column to inner column at footing level itself thru strap beam,, the base pressure could be approx P/A  ,,  but strap beam has to resist eccentric moment P*e as discussed in previous post.

Reiforcement is provided at top.,, bottom bars could be nominal ones.
Approx Moment in strap beam can be taken as M=P*e  with 10% reduction for soil passive relief,, but better workout passive relief from side wall in footing zone.

Shesr force - entire shear is balanced within the footing  being resisted by footing concrete ,, hence stps can be nominal but pl see some text book also for better understand ing of subject.

[vikram.jeet]

Very old posting from respected  BV Harsoda saheb  wherein discussion on edge footing was there :-

[vikram.jeet]

Earlier posting from my end :

Plinth beam at plinth level can also help , but in that case there is need to  
for additional forces to be taken into consideration .

There are two alternatives - - - - -

1 ] Alternative A - - Additional forces in Column , Plinth beam as well as check
of other columns on plinth beam grid

Provide additional reinf in column for eccentric moment M. This reinf needs to  
be provided from footing to plinth beam (with Ld embedment in both ), and
plinth beam need s to be designed for additional tensile force T= M/Df .  
The columns on inner side with which this plinth beam is tied also to be  
checked for a force T/N

Df is the foundation depth
( More precisely vertical distance from from CL of footing to CL of Plinth B)

N - - is the nos of other columns in that grid tied by plinth beam.

2 ] Alternative B - - Plinth beam designed as strap beam with filler 345thk
brick wall for light loadings/and pcc wall 1:3:6 for high loading between
footing -top and plinth -beam -underside.

This wall will be sandwiched between footing and plinth beam. This will be
subject to upward force =column load which in turn act on plinth beam
to be designed as strap beam.


best regds

vikramjeet



Dear Er vikram.jeet Sir If we provide Plinth beam instead of strap beam in case of eccentric footing so that it connects to inner column to take care of eccentric moment Please comment on this Regards
-- ­­

Posted via Email

[vikram.jeet]

Earlier posting of 31.05.2010

[vikram.jeet]

Situation now a days reg L footings :

In big projects with proper supervision , whatever detais a str engineer  give in drg ,, are followed without if / but.

But in projects where client is ignorant ,, no / poor supervision  ,, that too by non Civil er  ,, there are possibilities that Strap beams are not provided ,  and unless supervised ,, no body knows ,  Missing is due to fact that additional excavaton for strap beam right upto found lvl. Even many site ers have tendency to ignore here.
However in present times with what's app facility photos must be demanded by Str Consultant when reinf is placed and strap beam ,provided/ not can be easily seen distantly .

[ramu_se]

Thank you, Sir.

I will resolve one problem and update you.