Rein f Detail Footing Col

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Summary Sheet Session Number : Date : Subject Expert : 2 13.03.2007 Dr. M.C. Nataraja Dr. M.C. Nataraja Professor Department of Civil Engineering, S.J. College of Engineering, Mysore – 570 006. Phone:0821-2343521, 9880447742 E-mail: [email protected]

Transcript of Rein f Detail Footing Col

Page 1: Rein f Detail Footing Col

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: [email protected]

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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

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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

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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

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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.

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Combined footingsCombined footings

COMBINED FOOTING

COMBINED FOOTING

PROPERTY LINE

RECTANGULAR AND TRAPEZOIDAL TYPES

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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.

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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

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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

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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

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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

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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

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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

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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.

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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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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

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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

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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

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≤ 75 > 75

≤ 48φtr

Column steel detailingColumn steel detailing

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Column steel detailingColumn steel detailing

> 75

> 75

> 75> 75

≤ 48φtr > 48φtr > 48φtr

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Column steel detailingColumn steel detailing

≤ 48φtr

φtr

≤ 75

> 48φtr

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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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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

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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

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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