reinfdetailfootingcol.ppt [compatibility mode] [repaired]
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Summary SheetSession Number :
Date :
Subject Expert :
2
13.03.2007
Dr. M.C. NatarajaProfessor
Department of Civil Engineering,
S.J. College of Engineering,
Mysore 570 006.
Phone:0821-2343521, 9880447742
E-mail: nataraja96@yahoo.com
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Learning Outcomes:
After this students will be able to do the detailing ofdifferent types of isolated footings through drawingand bar bending schedule.
Detailing of Steel in Footings
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Footings
The function of a footing or a foundation is to transmit theload form the structure to the underlying soil.
The choice of suitable type of footing depends on the depth atwhich the bearing strata lies, the soil condition and the type ofsuperstructure.
Detailing of Steel in Footings
http://www.tekniksipil.org/civil-engineering/ -
Types of footing
Following are the different types of footing used for concrete structure
Isolated footing Combined footings Strap footing Mat or raft foundation Pile foundation
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Isolated footings
Isolated footings are provided under each column and may
be square, rectangular, or circular in plan. Footing may be
flat or tapered.
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Combined footings
COMBINEDFOOTING
COMBINED FOOTING
PROPERTY LINE
RECTANGULAR AND TRAPEZOIDAL TYPES
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Combined footings
Combined footings are provided to support two or morecolumn loads. These may be continuous with rectangularor trapezoidal in plan as shown. Combined footingsbecome necessary under the following circumstances:
when the isolated footings overlap.
when the exterior column is close to the property line withthe result symmetrical isolated footing can not beprovided.
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Strap footing Strap footing is one of the types of combined types of
combined. It consists of an isolated footing of twocolumns connected by a beam called strap beam. Thestrap beam does not remain in contact with the soil andthus does not transfer any load to the soil. This isprovided when one of the columns is on the propertyline.
STRAP FOOTING
STRAP BEAM
PROPERTY LINE
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Mat foundation
The is provided when the soil is havingvery low bearing capacity and or whencolumns loads are heavy, the requiredfooting area becomes very large anduneconomical.
MAT FOUNDATION
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Detailing Size of footing
Depth at footing
Depth of footing edge
Nominal and effective cover
Development length
Minimum and maximum steel
Spacing of bars and stirrupsPLAN
BM1OWS
TWS
d/2
d
BM2
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Detailing of steel in rectangularfooting as per IS:456-2000ReinforcementLong and short directionIn short direction larger steel area is needed in the central portion and is given by
Reminder of the steel in end bands
Development length= Ldt=
Ldt = 47s for M20 concrete and Fe 415 steel
=
d i r e c t is h o r tt o t a ls t
b a n dc e n t r a ls t
AA
,,
,
1)/(2+BL
bd4.f
ss
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PROBLEMAn isolated footing is to be provided for a column of section400 mm x 400 mm. The following details re given:
Height of the column =3mMain reinforcement in column = 4 Nos. 16 mm diameter.Transverse reinforcement = 6 mm at 220 mm c/cPlan size of footing = 2.7 m x 2.7 mDepth of footing at column face = 500 mmDepth of footing at edge = 150 mmDepth of foundation = 1000 mm
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Isolated footing Contd..Footing reinforcement = a mesh of 20 mm diameter steel at
250 mm c/c.
Grade of concrete= M20
Grade of steel = Fe415
Draw to a suitable scale the following:
Plan
Sectional Elevation
Prepare bar bending schedule 20 Marks
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Solution:Development length in tension = 47 = 47 x 16= 752 mm
Depth at junction = 500 mm
Leg length available for column bars = Ldt 500 = 252 mm < 300 mm.
Provide 300 mm minimum.
Development length of 20 mm bars in footing = 47 x 20 = 940 mm
This is provided by the horizontal projection of bars. Bars need not be bent at ends in to the depth of footing.
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Number of bars in footing = 11 Numbers at 200 mm c/c with a
side cover of 100 mm.
Width of footing= 10 x 250 + 100 x 2 =2700 mm
Follow all specification of SP 34 and prepare the drawing
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Detailing with dowel bars
Pu/bD < 0.45fck A1/A2
2:1
A1=bxD
A2= [b+4Df] x [D+4Df}
Df
2Df
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Bar bending scheduleFor exercise problem
For footing only
Member Mark No. of barsDiameter
in mm
Lengthin
m/piece
Total length in
mBar details Remarks
#20
FootingA 11 20 2.55 28.05 #20@250B 11 20 2.55 28.05 #20@250
Total length in m/diameter 56.10Weight in kg/m 2.45
Total weight in kg/diameter 137.45
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Estimation of quantity of concrete
Volume of concrete = L x B x D
L= length in mB=Breadth in mD=Thickness in m Apply for rectangular and trapezoidal part
Weight of concrete, kg = Volume x density
Slide Number 1Slide Number 2Slide Number 3Slide Number 4Isolated footingsCombined footingsCombined footingsStrap footingMat foundationDetailingDetailing of steel in rectangular footing as per IS:456-2000PROBLEMIsolated footing Contd..Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Detailing with dowel barsSlide Number 23Slide Number 24Estimation of quantity of concrete
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