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Eccentric Combined Footing

The document summarizes the design of an eccentric combined footing (CF1) to support two columns (A and B) with unfactored loads of 554.6 KN and 699.9 KN respectively. Key aspects of the design include: 1) Determining the load center location as 1.59 m from the left of column A. 2) Sizing the footing as 3.18 m long, 1.98 m wide, and 0.44 m deep to eliminate moment due to eccentricity and satisfy punching shear and bending moment criteria. 3) Calculating reinforcement as 2821.76 mm^2 of 20 mm diameter bars spaced at 150 mm to resist the maximum bending moment

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1K views3 pages

Eccentric Combined Footing

The document summarizes the design of an eccentric combined footing (CF1) to support two columns (A and B) with unfactored loads of 554.6 KN and 699.9 KN respectively. Key aspects of the design include: 1) Determining the load center location as 1.59 m from the left of column A. 2) Sizing the footing as 3.18 m long, 1.98 m wide, and 0.44 m deep to eliminate moment due to eccentricity and satisfy punching shear and bending moment criteria. 3) Calculating reinforcement as 2821.76 mm^2 of 20 mm diameter bars spaced at 150 mm to resist the maximum bending moment

Uploaded by

bishwaram gosain
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as XLSX, PDF, TXT or read online on Scribd
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P1= 369.7561 KN P2= 466.

6045 KN
A B
ECCENTRIC COMBINED FOOTING DESIGN (CF1)

GRADE OF CONCRETE M 20
YIELD STRESS= FE 500
BEARING CAPICITY OF SOIL= 150 KN/m2

LOADS: centre to centre distance between column= 2.8488 m


size of column A= 0.3048 m
AT COLUMN A= 554.6341 KN size of column B= 0.3048 m
AT COLUMN B= 699.9067 KN

TOTAL UNFACTORED COLUMN LOAD= 836.36053333 KN


10% OF COLUMN LOAD= 83.63605 KN

TOTAL LOAD = 919.9966 KN

CALCULATION OF LOAD CENTRE:


= 1.589342 m (FROM LEFT EDGE OF COLUMN A)

LENTH OF FOOTING TO ELIMINATE MOMENT DUE TO ECCENTRICITY= 3.178684 m

THIS MEANS CANTILEVER LENGTH OF 0.0250837175 m


CANTILEVER LENGTH FROM CENTRE OF COLUMN B= 0.177484

NOW, AREA REQUIRED= 6.133311 m2


LENGTH ADOPTED= 3.178684
HENCE WIDTH REQUIRED= 1.9295126923 m

SO ASSUME WIDTH OF= 1.9812 m

ACTUAL SOIL PRESSURE= 132.80606054 KN/m2 <150KN/m2


SOIL PRESSURE INTENSITY= 263.11536713 KN/m

SHEAR FORCE AND BM CALCULATION FROM LEFT SIDE:

AT CENTRE OF COLUMN A= 40.098781951 KN BM AT A= 3.055527 KNm


-329.65728472 KN

AT CENTRE OF COLUMN B= 419.90577317 KN BM AT B= 131.6055 KNm


-46.698693494 KN

POINT OF ZERO SHEAR FORCE= 1.2529 m BM AT POINT OF ZERO SF= -203.4583 KNm

SHEAR FORCE AND BM CALCULATION FROM RIGHT SIDE:

AT CENTRE OF COLUMN B= -46.698693494 KN BM AT B= 4.144129 KNm


419.90577317 KN

AT CENTRE OF COLUMN A= -329.65728472 KN BM AT A= -124.4058 KNm


40.098781951 KN

POINT OF ZERO SHEAR FORCE= 1.5959 m BM AT POINT OF ZERO SF= -330.9196 KNm

HENCE, MAXIMUM BM ARE: 197.40821121 KNm


AND
-496.37947491 KNm

DEPTH CALCULATION

1 FROM BENDING MOMENT CRITERIA:

DEPTH= 306.20675646 mm
ADOPT D= 500 mm
d= 440 mm
2 CHECK FROM PUNCHING SHEAR CRITERIA:

SHEAR STRENGTH OF CONCRETE= 0.25(fck)^0.5


1.118034 N/mm2

COLUMN FORCE= 554.6341 KN


SHEAR STRESS= 554.6341 /AREA

PERIMETER= 1795 mm
DEPTH= 440

PUNCHING AREA= 789800 mm2

SHEAR STRESS= 0.702246 N/mm2 < 1.118034 OKAY

REINFORCEMENT CALCULATION:

f y x A st
BM  0.87 x f y x A st x (d  )
f ck x b

ON SOLVING,

Ast= 2821.761 mm2 over the span of 1.9812 m

TAKE 20 mm dia. Bar


total no of rebar needed= 8.986499 spacing needed= 220.1333 mm
9 take spacing of= 150 mm
% of steel= 0.504286 %

SHEAR STRENGTH OF STEEL FOR 0.504286 % STEEL= 0.48 N/mm2


3 ONE WAY SHEAR CHECK:

SHEAR FORCENAT DISTANCE d FROM FACE OF COLUMN= 263.57 KN


SHEAR AREA= 871728 mm2

SHEAR STRESS= 0.302353 N/mm2 < 0.48 okay

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