rein f detail footing col
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Summary SheetSession Number
:Date :
Subject Expert :
2 13.03.2007 Dr. M.C. NatarajaDr. M.C. Nataraja
Professor
Department of Civil Engineering,
S.J. College of Engineering,
Mysore – 570 006.
Phone:0821-2343521, 9880447742
E-mail: nataraja96@yahoo.com
Learning Outcomes:
• After this students will be able to do the detailing of After this students will be able to do the detailing of different types of isolated footings through drawing different types of isolated footings through drawing and bar bending schedule. and bar bending schedule.
Detailing of Steel in FootingsDetailing of Steel in Footings
FootingsFootings
The function of a footing or a foundation is to transmit the
load form the structure to the underlying soil.
The choice of suitable type of footing depends on the depth at
which the bearing strata lies, the soil condition and the type of
superstructure.
Detailing of Steel in FootingsDetailing of Steel in Footings
Types of footingTypes 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
Isolated footingsIsolated footings
Isolated footings are provided under each column and may
be square, rectangular, or circular in plan. Footing may be
flat or tapered.
Combined footingsCombined footings
COMBINED FOOTING
COMBINED FOOTING
PROPERTY LINE
RECTANGULAR AND TRAPEZOIDAL TYPES
Combined footingsCombined footings
• Combined footings are provided to support two or more
column loads. These may be continuous with rectangular
or trapezoidal in plan as shown. Combined footings
become necessary under the following circumstances:
• when the isolated footings overlap.
• when the exterior column is close to the property line with
the result symmetrical isolated footing can not be
provided.
Strap footingStrap footing• Strap footing is one of the types of combined types of
combined. It consists of an isolated footing of two columns connected by a beam called strap beam. The strap beam does not remain in contact with the soil and thus does not transfer any load to the soil. This is provided when one of the columns is on the property line.
STRAP FOOTING
STRAP BEAM
PROPERTY LINE
Mat foundationMat foundation
• The is provided when the soil is having very low bearing capacity and or when columns loads are heavy, the required footing area becomes very large and uneconomical.
MAT FOUNDATION
DetailingDetailing
• 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
Detailing of steel in rectangular Detailing of steel in rectangular footing as per IS:456-2000footing 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 = 47φs for M20 concrete and Fe 415 steel
directionshorttotalst
bandcentralst
A
A
,,
,
1)/(
2
BL
bd4
.φf
τss
PROBLEMPROBLEM
An isolated footing is to be provided for a column of section 400 mm x 400 mm. The following details re given:
Height of the column =3m
Main reinforcement in column = 4 Nos. 16 mm diameter.
Transverse reinforcement = 6 mm at 220 mm c/c
Plan size of footing = 2.7 m x 2.7 m
Depth of footing at column face = 500 mm
Depth of footing at edge = 150 mm
Depth of foundation = 1000 mm
Isolated footing Isolated footing Contd..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
Solution:Solution:
Development length in tension = 47φ = 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.
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
Square footingSquare footing
GROUND LEVEL
CROSS SECTION
SECTIONAL ELEVATION
LEVELLING COURSE
DEPTH OFFOUNDATION
≥ 500 mm
Ldt L dc
400
Ldt
300 min.
150 min.
75
75
4- #16
#6@220
#20@250
4- #16
3000 mm
PLAN
2700
2700
400
GROUND LEVEL
CROSS SECTION
SECTIONAL ELEVATION
LEVELLING COURSE
DEPTH OFFOUNDATION
≥ 500 mm
Ldt L dc
Ldt
300 min.75
75
6- #20
#8@200
#16@200
300
75
PLAN
PLAN
400
Rectangular footingRectangular footing
Rectangular footingRectangular footing
GROUND LEVEL
CROSS SECTION
SECTIONAL ELEVATION
LEVELLING COURSE
DEPTH OFFOUNDATION
≥ 500 mm
Ldt L dc
Ldt
300 min.75
75
6- #20 #8@200
#16@200
300
75
PLAN
3200
2200
CB= 2200
EB EB
≤ 75 > 75
≤ 48φtr
Column steel detailingColumn steel detailing
Column steel detailingColumn steel detailing
> 75
> 75
> 75> 75
≤ 48φtr > 48φtr > 48φtr
Column steel detailingColumn steel detailing
≤ 48φtr
φtr
≤ 75
> 48φtr
Detailing with dowel bars
Pu/bD < 0.45fck √A1/A2
2:1
A1=bxD
A2= [b+4Df] x [D+4Df}
Df
2Df
SECTIONAL ELEVATION
LEVELLING COURSE
DEPTH OFFOUNDATION
≥ 500 mm
Ldt L dc
Ldt
300 min.75
75
#16@200
75
Detailing with dowel bars
LAP
Dowel bars or starter bars
Bar bending scheduleFor exercise problem
For footing only
Member MarkNo. of bars
Diameterin 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
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
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