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Raft foundation design
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es_jayakumar
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PostPosted: Sun Jan 31, 2016 3:07 pm    Post subject: Reply with quote

A small Excel sheet prepared to verify the adequacy of the thickness of the raft provided for a slab type raft foundation, based on punching shear criterion, is enclosed.


E S Jayakumar



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Design of Raft Thickness.xls
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SADATCHARAMOURTHY
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Joined: 20 Jun 2009
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PostPosted: Thu Feb 25, 2016 5:19 am    Post subject: Reply with quote

Dear mohd_arastu

It's my humble request to send me your Excel sheet of Raft design on my below mail ID.

My Email ID is sadatcharamourthy@yahoo.com
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ynagaraju
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Joined: 25 Apr 2016
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PostPosted: Mon Apr 25, 2016 2:57 pm    Post subject: Re: Excel sheet of Raft design Reply with quote

Dear mohd_arastu

It's my humble request to send me your Excel sheet of Raft design on my below mail ID.

My Email ID is archiedesigners1@gmail.com
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monikabothra
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PostPosted: Sat Apr 30, 2016 12:17 pm    Post subject: Raft / Strap Design Reply with quote

Dear mohd_arastu

It's my humble request to send me your Excel sheet of Raft design on my below mail ID.

My Email ID is monikabothra@ymail.com
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prash1730
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PostPosted: Sat Nov 07, 2020 2:45 pm    Post subject: Reply with quote

Dear mohd_arastu,
Thanks a lot for preparing a spreadsheet spreadsheet for raft design. Request you to send a copy of the same to prash1730@gmail.com


Best regards,
PNP
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VPandya
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Joined: 09 Nov 2009
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PostPosted: Tue Nov 10, 2020 5:04 am    Post subject: STAAD/PRO RAFT FOUNDATION WITH PLATE ELEMENT EXAMPLE Reply with quote

Dear Sefi Friends ,

I have used  STAAD/PRO  PLATE ELEMENTS WITH WINKLER SPRINGS, (MODULUS OF SUBGRADE REACTION , SOIL SPRINGS) FOR  HIGH RISE BUILDING WITH MANY COLUMNS,  RAFT FOUNDATION . DESIGNED WITH ACI 318-08 Code . I am giving here a Link from STAAD/PRO on RAFT FOUNDATION EXAMPLE :

Link:  



https://youtube.com/watch?v=_KvR3tYRvjA  

Note :  Link will tell  you how to create STAAD/PRO model .  If does not work contact STAAD/PRO HELP .



Regards.

Vasudeo Pandya  P.E.
Structural Engineer
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Moosewala
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PostPosted: Mon Jan 03, 2022 12:47 pm    Post subject: Reply with quote

Sir,


Can we use the emperical formulas as given by E. Bowles using bearing capacity https://snaptube.cam/ of soil to calculate modulas of subgrade reaction? if yes, To what extent the values should be assumed to be appropriate ?


Regards.
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vikram.jeet
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PostPosted: Tue Jan 04, 2022 5:42 am    Post subject: Reply with quote

STRUCTURE AND GEOTECHNICAL COMBINE

MODULUS OF SUBGRADE REACTION
The modulus of subgrade reaction is very important soil/rock parameter.

MODULUS K = (LOAD/AREA) /( CORRESPONDING SETTLEMENT)

Generally for field tests on 75cm  circular plate , pressure for 1.25mm Settlement is taken .
Then  K = p/0.125  MPA/cm =  10p / 0.125   kg/cm2/cm
P is the pressure for a settlement of 1.25mm on plate

REFER IS 9214 FOR DETERMINATION OF K VALUE


USEFUL SOIL DATA (AS PER SP-7, NBC OF INDIA)

COHESION LESS SOIL

LOOSE SOIL
RELATIVE DENSITY  < 20%
SPT N VALUE (BLOWS/30CM)   < 10
MODULUS OF SUBGRADE REACTION K   15000KN/m3(DRY,MOIST)
MOD OF SUBGRADE REACTION K   9000 kN/m3 (Submerged state)

MEDIUM SOILS
RD 20% TO 70%
SPT N VALUE    10 TO 30
K (DRY/MOIST) -  15000  - 47000 KN/m3
K (Submerged state) -  9000 - 29000 kN/m3

DENSE SOILS
RD> 70%
SPT N VALUE >30
K (DRY/MOIST) -  47000 - 180000 kN/m3
K (Submerged)  29000 - 108000  kN/m3

ALL ABOVE DATA IS FOR COHESION LESS SOILS



USEFUL SOIL DATA (AS PER SP-7 )

COHESIVE SOILS

SOFT TO VERY SOFT SOILS
SPT N VALUE  < 4

UNCONFINED COMPRESSIVE STRENGTH - NOT GIVEN , MUST BE SMALL
MODULUS OF SUBGRADE REACTION K - NOT GIVEN



MEDIUM SOILS
SPT N VALUE   4  TO  8

UNCONFINED COMPRESSIVE STRENGTH  Not given , but seems < 100 kN/m2 , since stiff values are given in range 100 - 200 kN/m2.

K  value - not given , but seem  < 27000 kN/m3 looking at range of stiff values


STIFF SOILS
SPT N VALUE  8  TO  15
UCS  100  -  200 KN/m2
Modulus of subgrade reaction K value    27000 kN/m3


VERY STIFF SOILS
SPT N VALUE  >  15
UCS   200 - 400 KN/m2
Mod of subgrade reaction K value  27000 to 54000 kN/m3


HARD SOILS
SPT N VALUE  > 15
UCS  > 400 KN/m2
Mod of subgrade reaction K   54000 to 108000 kN/m3

UCS VALUES AND K VALUES ARE ON SQ PLATE 300X300MM
AV LOAD INTENSITY TO BE LESS THAN (ULTIMATE BC/2)


FOR MORE INFO REFER SP7 CHAPTER 6 ANNEXURE B
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vikram.jeet
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PostPosted: Tue Jan 04, 2022 5:45 am    Post subject: Reply with quote

MODULUS OF SUBGRADE REACTION

EMPIRICAL FORMULA FOR CALCULATING MODULUS K

K= 0.65 {(Es*B^4)/(E I)}^(1/12) *  Es/(1 - u^2)  * 1/B

Approximately K can be taken as
K = 0.65 * Es/(1 - u^2)  * 1/B
(1/12 the power term taken as nearly unity)

Es - Modulus of Elasticity of soil
E - Young's modulus of foundation material
u - Poisson ratio of soil
B - Foundations width
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vikram.jeet
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PostPosted: Tue Jan 04, 2022 5:47 am    Post subject: Reply with quote

MODULUS OF SUBGRADE REACTION

FOR RIGID FOUNDATIONS :
MODULUS K = ( Average contact pressure)/(average settlement )

The ultimate BC  = SBC* FOS


MODULUS K =( SBC * FOS) /(PERMISSIBLE SETTLEMENT)

The formula given by Foundation Design book by BOWELS is based on this.
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