Design of RCC slab culvert in Narsapur area

Construction of 6.00mts span culvert at 6/0 KM of Vemuladeevi channel Name of the work:-Road from R&B Road to SC colony of Pedalanka.

n of 6.00mts span culvert at 6/0 KM of Vemuladeevi channel

he work:-Road from R&B Road to SC colony of Pedalanka.

Design Philosophy:-

The design of 1V-- 6.37m right span culvert is carried as per the procedure out lined below:Step1:The design discharge was fixed after arriving discharge based on the following methods:a.As per the hydraulic particulars furnished by the Irrigation department b.By Area-Velocity method using Manning's equation for arriving at the flow velocity and area by considering actual cross-section of the channel. Step2:a.Hydraulic particulars like HFL,OFL are obtained from Irrigation department. b.Bottom of deck level was fixed based on HFL and road formation levels on both sides. The vertical clearence and afflux are verified. c.Ventway calculations are done for fixation of ventway. d.Normal scour depth with reference to HFL was calculated using Lacey's equations e.After arriving at the Maximum scour depth,bottom level of the foundation was fixed below the maximum scour depth Step3:After arriving at bottom of deck level,bottom of foundation level and required ventway,the dimensions of the bridge are finalised. The structural components are desined in the following manner:a.As per the recommendations of IRC 6:2000,IRC class A live load required for bridges and culverts of medium importance is selected. b.Load combination is selected as per IRC 6:2000 c.Based on the trial pit particulars and soil test reports,type of foundation was selected. d.The structural components like Abutment,raft foundation are designed as per the guide lines given in relevent IRC codes. e.The deck slab is proposed as per the MOST drawing Nos.BD 1-74&BD 2-74 f.The dirt wall is proposed as per the drawings given in Plate No.7.25 of IRC:SP20-2002(Rural roads manual)

Design of Abutments I)Design Parameters:Clear Right Span

=

6.00m

Deck slab length

=

6.740m

Width of the carriage way

=

5.50m

Thickness of deck slab as per MOST Dg.BD 1-74

=

0.515m

Thickness of wearing coat

=

0.075m

Height of railing

=

1.200m

Thickness of dirt wall

=

0.30m

Sectional area of dirt wall

=

0.360sqm

Thickness of RAFT footing

=

0.50m

Height of abutments

=

1.804m

Top width of abutments

=

0.690m

Bottom width of abutments

=

2.00m

Sectional area of abutment section

=

2.426sqm

Bank side batter of abutment

=

1.310m

Stream side batter of abutment

=

0.000m

Width of 1st footing

=

2.30m

Thickness of 1st footing

=

0.30m

Canal side offset of 1st footing wrt abutment

=

0.15m

Bank side offset of 1st footing wrt abutment

=

0.15m

Width of 2nd footing

=

2.45m

Thickness of 2nd footing

=

0.30m

Canal side offset of 2nd footing wrt abutment

=

0.30m

Bank side offset of 2nd footing wrt abutment

=

0.15m

Width of 3rd footing

=

0.00m

Thickness of 3rd footing

=

0.00m

Canal side offset of 3rd footing wrt abutment

=

0.00m

Bank side offset of 3rd footing wrt abutment

=

0.00m

Width of VRCC RAFT footing

=

6.55m

Thickness of VRCC RAFT footing

=

0.60m

Type of bearings

=

Unit weight of RCC (yrc)

=

25KN/cum

Unit weight of PCC (ypc)

=

24KN/cum

Density of back fill soil behind abutments (y)

=

18KN/Cum

Unit weight of water (yw)

=

10KN/Cum

Angle of shearing resistance of back fill material(Q)

=

30

(As per hydralic calculations)

No bearings proposed

Angle of face of wall supporting earth with horizontal(In degrees)(in clock wise direction)(a)

=

54.04

Slope of back fill (b)

=

0

Angle of wall friction (q)

=

15

Height of surcharge considered (h3)

=

1.20m

Road crest level (RTL)

=

2.577m

Low bed level (LBL)

=

0.477m

High flood Level (HFL) Bottom of foundation level (BFL) Safe Bearing Capacity of the soil (SBC)

= = =

1.477m -0.923m 6.00t/sqm

Compressive strength of concrete for RCC Strip footing (fck)

=

25.00N/sqmm

Yield strength of steel (fy) Cover to reinforcement

=

415.00N/sqmm

=

50.00mm

II)General loading pattern:As per IRC:6---2000,the following loadings are to be considered on the bridge or slab culvert:1.Dead load 2.Live load 3.Impact load 4.Wind load 5.Water current 6.Tractive,braking effort of vehicles&frictional resistance of bearings 7.Buoyancy 8.Earth pressure 9.Seismic force 10.Water pressure force

As per clause 202.3,the increase in permissible stresses is not permissible for the above loading combination.

III)Loading on the slab culvert for design of abutments:1.Dead Load:i)Self wieght of the deck slab =

238.64KN

ii)Self wieght of dirtwall over abutment =

49.50KN

iii)Self weight of wearing coat =

34.76KN

322.90KN There is no need to consider snow load as per the climatic conditions Self wieght of the abutments upto bottom most footing based on the preliminary section assumed:-

iv)Self wieght of the abutment section =

320.23KN

v)Self wieght of top footing =

91.08KN

vi)Self wieght of 2nd footing =

97.02KN

vii)Self wieght of 3rd footing =

0.00KN

viii)Self wieght of 4th footing =

0.00KN

508.33KN

W1

W1

ix)Calculation of eccentricity of self weight of abutment w.r.t base of abutment S.No

Description Load in KN

Distance of centroid of load from toe of abutment

Moment

1

Back batter(W1)

155.97384

1.127

175.78

2

Centre portion(W2)

164.30832

0.345

56.69

3

Front batter(W3)

0

0

0

320.28216

232.47

Location of resultant from toe of abutment =

0.73m

Eccentricity wrt centre of base of abutment =

0.270m

x)Calculation of eccentricity of self weight of abutment&1st footing w.r.t bottom of 1st footing S.No

Description Load in KN

Distance of centroid of load from toe of 1st footing

Moment

1

Back batter

155.97384

1.277

199.18

2

Centre portion 164.30832

0.495

81.33

3

Front batter

0

0

0

4

1st footing

91.08KN

1.15

104.74

411.36216

385.25

Location of resultant from toe of abutment =

0.94m

Eccentricity wrt centre of 1st footing=

0.210m

xi)Calculation of eccentricity of self weight of abutment,1st&2nd footings w.r.t bottom of 2nd footing

S.No

Description Load in KN

Distance of centroid of load from toe of 2nd footing

Moment

1

Back batter

155.97384

1.427

222.57

2

Centre portion 164.30832

0.645

105.98

3

Front batter

0

0.3

0

4

1st footing

91.08KN

1.300

118.4

5

2nd footing

97.02KN

1.225

118.85

508.38216

565.8

Location of resultant from toe of abutment =

1.11m

Eccentricity =

0.115m

xii)Calculation of eccentricity of self weight of abutment,1st&2nd footings w.r.t bottom of 2nd footing S.No

1 2 3 4 5 6

Description Load in KN

Back batter Centre portion Front batter 1st footing 2nd footing 3rd footing

Distance of centroid of load from toe of 3rd footing

0 0 0 0 0 0 0

Moment

1.427 0.645 0.3 1.00 0.93 0.00

0 0 0 0 0 0 0

Location of resultant from toe of abutment =

0.00m

Eccentricity =

0.000m

2.Live Load:As per clause 201.1 of IRC:6--2000,the bridges and culverts of medium importance are to be designed for IRC Class A loading. GENERAL IRC Class-A loading Pattern

6.8t

6.8t

3.00

3.00

6.8t

11.4t

3.00

6.8t

4.30

1.20

11.4t

3.20

2.7t

1.80

2.7t

1.10

1.80 3.00

6.8t

3.00

6.8t

4.30

6.8t

1.20

6.8t

3.20

11.4t

11.4t

2.7t

2.7t

1.10 3.00

The IRC Class A loading as per the drawing is severe and the same is to be considered as per clauses 207.1.3&207.4

Y 475

11.4t

11.4t

Portion to be loaded with 5KN/m² live load

8000

6.8t

6.8t

X

5500 3525

The ground contact area of wheels for the above placement,each axle wise is given below:Axle load (Tonnes) 11.4 6.8 2.7

Ground Contact Area B(mm)

250 200 150

W(mm)

500 380 200

Assuming 0.475m allowance for guide posts/kerbs and the clear distance of vehicle from the edge of guide post being 0.15m as per clause 207.1,the value of 'f' shown in the figure will be 0.625m

Hence,the width of area to be loaded with 5KN/m2 on left side is (f) =

0.625m

Similarly,the area to be loaded on right side (k) =

3.525m 4.15m

The total live load on the deck slab composes the following components:1.Wheel loads----Point loads

364.00KN

2.Live load in remaing portion(Left side)----UDL

21.06KN

2.Live load in remaing portion(Right side)----UDL

118.79KN 503.86KN

Resultant live load:Eccentricity of live load w.r.t y-direction(Along the direction of travel of vehicles) Taking moments of all the forces w.r.t y-axis S.No

Wheel Load/UDL in KN

Distance from Y-axis

1

57

0.875m

49.88KNm

2

57

0.875m

49.88KNm

3

57

2.675m

152.48KNm

4

57

2.675m

152.48KNm

5

34

0.875m

29.75KNm

6

34

0.875m

29.75KNm

7

34

2.675m

90.95KNm

8

34

2.675m

90.95KNm

9

21.0625

0.313m

6.58KNm

10

118.7925

4.688m

556.84KNm

503.855 Distance of centroid of forces from y-axis

Moment

1209.52KNm

= 2.401m Eccentricity =

0.824m

Eccentricity of live load w.r.t x-direction(At right angle to the travel of vehicles) Taking moments of all the forces w.r.t x-axis S.No

Load in KN

Distance from X-axis

Moment

1

57

9.005m

513.29KNm

2

57

9.005m

513.29KNm

3

57

7.805m

444.89KNm

4

57

7.805m

444.89KNm

5

34

3.505m

119.17KNm

6

34

3.505m

119.17KNm

7

34

0.505m

17.17KNm

8

34

0.505m

17.17KNm

9

21.06KN

4.690m

98.78KNm

10

118.79KN

4.690m

557.14KNm

503.855

2844.94KN

Distance of centroid of forces from x-axis

= 5.646m 0.956m

Eccentricity =

Y

Location of Resultant

2524 8000

5574

X

Location of Resultant

2524 8000

5574

X

5500

Calculation of reactions on abutments:-

Reaction due to loads Ra =

299.41KN

Reaction due to point loads = Rb =

204.44KN

Hence,the critical reaction is Ra =

299.4KN

The corrected reaction at obtuse corner =

299.41KN

Assuming that the live load reaction acts at the centre of the contact area on the abutment,

300 185

300

815 815 740

815 815 740

The eccentricty of the line of action of live load at bottom of abutment = 0.815m ----do----on top of 1st footing

=

0.815m

----do----on top of 2nd footing

=

0.740m

The eccentricity in the other direction need not be considered due to high section modulus in transverse direction.

3.Impact of vehicles:As per Clause 211 of IRC:6--2000,impact allowance shall be made by an increment of live load by a factor 4.5/(6+L) Hence,the factor is

0.353

Further as per clause 211.7 of IRC:6--2000,the above impact factor shall be only 50% for calculation of pressure on piers and abutments just below the level of bed block.There is no need to increase the live load below 3m depth. As such,the impact allowance for the top 3m of abutments will be

0.1765

For the remaining portion,impact need not be considered.

4.Wind load:The deck system is located at height of (RTL-LBL)

2.10m

The Wind pressure acting on deck system located at that height is considered for design. As per clause 212.3 and from Table .4 of IRC:6---2000,the wind pressure at that hieght is= 59.48 Kg/m2. Height of the deck system = Breadth of the deck system =

1.790 7.38

The effective area exposed to wind force =HeightxBreadth = Hence,the wind force acting at centroid of the deck system = (Taking 50% perforations)

3.91KN

Further as per clause 212.4 of IRC:6---2000 ,300 Kg/m wind force is considered to be acting at a hieght of 1.5m from road surface on live load vehicle. Hence,the wind force acting at 1.5m above the road surface =

16.50KN

The location of the wind force from the top of RCC strip footing =

4.79m

5.Water current force:Water pressure considered on square ended abutments as per clause 213.2 of IRC:6---2000 is P = 52KV2 =

24.18 Kg/m2.

(where the value of 'K' is 1.5 for square ended abutments) For the purpose of calculation of exposed area to water current force,only 1.0m width of abutment is considered for full hieght upto HFL Hence,the water current force =

0.51KN

Point of action of water current force from the top of RCC raft footing =

2.90m

6.Tractive,braking effort of vehicles&frictional resistance of bearings:The breaking effect of vehicles shall be 20% of live load acting in longitudinal direction at 1.2m above road surface as per the clause 214.2 of IRC:6--2000.

As no bearings are assumed in the present case,50% of the above longitudinal force can be assumed to be transmitted to the supports of simply supported spans resting on stiff foundation with no bearings as per clause 214.5.1.3 of IRC:6---2000

Hence,the longitudinal force due to braking,tractive or frictional resistance of bearings transferred to abutments is 50.39KN

The location of the tractive force from the top of RCC raft footing =

4.49m

7.Buoyancy :As per clause 216.4 of IRC:6---2000,for abutments or piers of shallow depth,the dead weight of the abutment shall be reduced by wieght of equal volume of water upto HFL. The above reduction in self wieght will be considered assuming that the back fill behind the abutment is scoured. For the preliminary section assumed,the volume of abutment section is i)Volume of abutment section =

13.34Cum

ii)Volume of top footing =

3.80Cum

iii)Volume of 2nd footing =

4.04Cum

iv)Volume of 3rd footing =

0.00Cum

v)Volume of 4th footing =

0.00Cum 21.18Cum

Reduction in self wieght =

211.80KN

8.Earth pressure :As per clause 217.1 of IRC:6---2000,the abutments are to be designed for a surcharge equivalent to a back fill of hieght 1.20m behind the abutment. The coefficient of active earth pressure exerted by the cohesion less back fill on the abutment as per the Coulomb's theory is given by '2 Ka =

Sin(a+Q) sina

sin(a-q)

sin(Q+q)sin(Q-b) sin(a+b)

Sin(a+Q) = Sin(a-q) = Sina = Sin(Q+q) = Sin(Q-b) = Sin(a+b) =

SIN[3.14*(54.04+30)/180] = SIN[3.14*(54.04-15)/180] = SIN[3.14*(54.04)/180] = SIN[3.14*(30+15)/180] = SIN[3.14*(30-0)/180] = SIN[3.14*(54.04+0)/180] =

0.961 0.875 0.97 0.707 0.5 0.97

From the above expression, Ka =

0.71

The hieght of abutment above GL,as per the preliminary section assumed = Hence,maximum pressure at the base of the wall

Pa =

The pressure distribution along the height of the wall is as given below:Surcharge load =

1.804m

15.34 KN/sqm

15.34

1.804

23.06KN/sqm

23.06

15.34

Area of the rectangular portion = Area of the triangular portion =

27.67 20.8 48.47

Taking moments of the areas about the toe of the wall S.No 1 2

Description

Area

Lever arm Moment

Rectangular Triangular

27.67 20.80

0.902 24.95834 0.60133333 12.50773333

48.47

37.46607333

Height from the bottom of the wall =

0.77m

The active Earth pressure acts on the abutment as shown below:-

0.70

50.96 1.804m 0.77m 54.04

2.00 0.56 Total earth pressure acting on the abutment P =

266.60KN

Horizontal component of the earth pressure Ph =

168.01KN

Vertical component of the earth pressure Pv =

206.99KN

Eccentricity of vertical component of earth pressure =

0.44m

9.Siesmic force :As per clause 222.1 of IRC:6---2000,the bridges in siesmic zones I and II need not be designed for siesmic forces.The location of the slab culvert is in Zone-I.Hence,there is no need to design the bridge for siesmic forces.

10.Water pressure force:The water pressure distribution on the abutment is as given below:-

HFL 1.48m

2.40

BFL -0.92m

24.00kn/sqm

Total horizontal water pressure force = The above pressure acts at height of H/3 =

158.40KN 0.80m

IV)Check for stresses for abutments&footings:-

a)Load Envelope-I:-(The Canal is dry,back fill scoured with live load on span) i)On top of RCC raft The following co-ordinates are assumed:a)x-Direction-----At right angle to the movement of vehicles b)y-Direction-----In the direction of movement of vehicles Vertical forces acting on the abutment (P) composes of the following components S.No

Intensity in KN

Type of load

Eccentricty about x- Eccentricty about yaxis(m) axis(m)

1

Reaction due to dead load from super structure

322.90KN

-0.740

0.00

2

Self wieght of abutment&footings

508.38KN

0.115

0.000

3

Reaction due to live load with impact factor---(Wheel loads+UDL)

-0.740

0.000

4

Impact load

0.00

0.00

405.10KN 0.00 1236.38

Horizontal forces acting/transferred on the abutment (H) composes of the following components S.No

Type of load

Intensity in KN

Direction x or y

Location(Ht.from the section considered).(m)

1

Wind load

16.50KN

x-Direction

4.79

2

Tractive,Braking&Frictional resistance of bearings

50.39KN

y-Direction

4.49

3

Water current force

0.51KN

x-Direction

2.90

Check for stresses:About x-axis:Breadth of 2nd footing b =

6.25m

Depth of 2nd footing d =

2.45m

Area of the footing = A =

15.3125 m2

Section modulus of bottom footing about x-axis --Zx =

2

(1/6)bd =

6.25 m3

For M15 grade of concrete permissible compressive stress in direct compreession is 4N/mm 2 i.e, 4000KN/sqm For M15 grade of concrete permissible tensile stress in bending tension is -2N/mm

2

i.e, -2000KN/sqm S.No

1 2 3 4 5

Intensity in KN (P)

Type of load

Vertical loads:-(Stress = P/A(1+6e/b) Reaction due to dead load from super structure Self wieght of abutment&footings Reaction due to live load with impact factor Impact load Horizontal loads:- (Stress = M/Z) Tractive,Braking&Frictional resistance of bearings

Eccentricity/Lever arm

Stress at heel P/A(1+6e/b)

322.90KN 508.38KN 405.10KN 0.00KN

-0.740 0.115 -0.740 0.000

6.11 36.87 7.66 0

50.39KN

4.49

-36.18 14.46

S.No

1 2 3 4 5

Intensity in KN (P)

Type of load

Vertical loads:-(Stress = P/A(1+6e/b) Reaction due to dead load from super structure Self wieght of abutment&footings Reaction due to live load with impact factor Impact load Horizontal loads:- (Stress = M/Z) Tractive,Braking&Frictional resistance of bearings

Eccentricity

Stress at toe P/A(1+6e/b)

322.90KN 508.38KN 405.10KN 0.00KN

0.740 -0.115 0.740 0.000

36.07 29.54 45.25 0

50.39KN

4.49

36.18 147.04

Stress at heel =

P/A(1+6e/b)+M/Z =

14.46 KN/Sqm>-2000KN/sqm.

Hence safe. Stress at toe =

P/A(1+6e/b)+M/Z =

147.04 KN/Sqm-2000KN/sqm.

Hence safe. Stress at down stream side edge =

P/A(1+6e/b)+M/Z =

85.8 KN/Sqm-2000KN/sqm.

Hence safe. Stress at toe =

P/A(1+6e/b)+M/Z =

147.78 KN/Sqm-2000KN/sqm.

Hence safe. Stress at down stream side edge of abutment =

P/A(1+6e/b)+M/Z =

84.3 KN/Sqm-2000KN/sqm.

Hence safe. Stress at toe =

P/A(1+6e/b)+M/Z =

169.82 KN/Sqm-2000KN/sqm.

Hence safe. Stress at down stream side edge of abutment =

P/A(1+6e/b)+M/Z =

89.26 KN/Sqm-2000KN/sqm.

Hence safe. Stress at toe =

P/A(1+6e/b)+M/Z =

Hence safe.

About y-axis:-

77.73 KN/Sqm-2000KN/sqm.

Hence safe. Stress at down stream side edge of abutment =

P/A(1+6e/b)+M/Z =

Hence safe.

ii)On top of 2nd footing The following co-ordinates are assumed:a)x-Direction-----At right angle to the movement of vehicles b)y-Direction-----In the direction of movement of vehicles

59.03 KN/Sqm-2000KN/sqm.

Hence safe. Stress at toe =

P/A(1+6e/b)+M/Z =

83.44 KN/Sqm-2000KN/sqm.

Hence safe. Stress at down stream side edge of abutment =

P/A(1+6e/b)+M/Z =

62.53 KN/Sqm-2000KN/sqm.

Hence safe. Stress at toe =

P/A(1+6e/b)+M/Z =

77.89 KN/Sqm-2000KN/sqm.

Hence safe. Stress at down stream side edge of abutment =

P/A(1+6e/b)+M/Z =

58.25 KN/Sqm 2.0 Hence safe (As per clause 706.3.4 of IRC:78-2000)

Check for stability against sliding:Total vertical load acting on the base of the abutment Vb =

1255.22KN

Total sliding force,ie,horizontal load on the abutment Hb =

234.90KN

Coefficient of friction between concrete surfaces = Factor of safety against sliding F s =

4.27491751 > 1.5 Hence safe (As per clause 706.3.4 of IRC:78-2000)

b)Load Envelope-IV:-(The Canal is running upto HFL with no live load on span) The following co-ordinates are assumed:-

0.80

a)x-Direction-----At right angle to the movement of vehicles b)y-Direction-----In the direction of movement of vehicles Vertical load acting on the abutment (P) composes of the following components S.No

1

Intensity in KN

Type of load

Reaction due to dead load from super structure

322.90KN

Self wieght of abutments

320.23KN

Reduction in self weight due to buoyancy

-133.40KN

2

Net self wieght

3

Vertical component of Active Earth pressure

Eccentricty about x- Eccentricty about yaxis(m) axis(m) 0.82

0.00

186.83KN

0.270

0.000

206.99

0.440

0.00

Horizontal load acting/transferred on the abutment (H) composes of the following components S.No

Intensity in KN

Type of load

Direction x or y

Location(Ht.from the section considered).(m)

1

Wind load

16.50KN

x-Direction

4.19

2

Tractive,Braking&Frictional resistance of bearings

0.00KN

y-Direction

0.00

3

Active Earth pressure force

168.01KN

y-Direction

0.77

4

Force due to water pressure

158.40KN

y-Direction

0.20

Check for stability against over turning:Taking moments of all the overturning forces about toe of the abutment wrt x-axis, Moment due to tractive,braking&frictional resistance of bearings = Moment due to active earth pressure force =

Total overturning moment =

0.00Kn-m 129.87Kn-m

129.87Kn-m

Taking moments of all the restoring forces about toe of the abutment wrt x-axis, Moment due to self weight of abutment =

237.27Kn-m

Moment due to water pressure force on the abutment =

31.68Kn-m

Moment due to super structure load reaction on abutment =

586.05Kn-m

Moment due to vertical component of active earth pressure =

298.07Kn-m

Total Restoring moment =

1153.08Kn-m

Factor of safety =

8.87855106

> 2.0 Hence safe (As per clause 706.3.4 of IRC:78-2000)

Check for stability against sliding:Total vertical load acting on the base of the abutment Vb =

552.22KN

Total sliding force,ie,horizontal load on the abutment Hb =

168.01KN

Coefficient of friction between concrete surfaces = Factor of safety against sliding F s =

2.62940787 > 1.5 Hence safe (As per clause 706.3.4 of IRC:78-2000)

0.80

DESIGN OF RAFT FOR THE SLAB CULVERT Name of the work:-Slab culvert on Vemuladeevi Channel Abutment Abutment

Length of the Raft:-

=

12.60m

Width of the Raft:-

=

6.55m

Total load on the Raft:Dead Load:Wt.of Deck slab =

477.28Kn

Wt.of wearing coat =

69.51Kn

Wt.of bed blocks over abutments =

99.00Kn

Wt.of abutments Footing-I = Footing-II = Wt.of abutments =

182.16Kn 194.04Kn 640.46Kn

Total Dead load stress =

20.14Kn/Sqm

Live Load:Taking IRC Class-A loading Wheel width in the direction of movement =0.2+0.2+0.25/2 = 0.625m

11.4

11.4 1.2

0.625

6.8 4.3

6.8 3.0

6.8 3.0

0.475

1662.45Kn

12.60m

Centre of gravity of loading from 1st 11.4t load = =

4.33m

Centre of gravity from the end of raft =

4.955m

Eccentricity =

1.345m

Stress due to live load = 1xP(1+6e/b) (Taking single lanes) A Max.stress =

11.45Kn/Sqm

Min.stress =

-0.78Kn/Sqm

Total stress due to dead load and live load Max.Stress =

31.59Kn/Sqm

Min.Stress =

19.36Kn/Sqm

Assuming the depth of raft as 60cm Stress due to self weight of raft =

15.00Kn/Sqm

Stress due to wieght of base concrete =

7.20Kn/Sqm

Hence,the Max.stress on the soil =

53.79Kn/Sqm Which is less than 6t/sqm(Soil testing report)

Hence safe. Net Max.upward pressure acting on Raft =

31.59Kn/Sqm

Net Min.upward pressure acting on Raft =

19.36Kn/Sqm

The design stress =

25.48Kn/Sqm

Hence,the UDL on the raft =

25.48Kn/m

Design of Raft:The raft will be analysed as a continuous beam of 1m width with the loading as shown below:-

1.30

10.00

1.30

UDL of 25.48Kn/m After analysis the bending moment diagram is as given below:

517

37.5

Max.Negative bending moment Mu =

517.00KNm

Max.Positive bending moment Mu =

37.50KNm

Effective depth required d = Over all depth provided =

Mu/0.138fckb =

387.11mm

600.00mm

Effective depth provided(Assuming 40mm cover) d =

542.00mm

Bottom steel:Mu/bd2 =

1.76

From table 3 of SP 16,percentage of steel required = Area of steel required =

0.535 2899.70sqmm

Top steel:Mu/bd2 =

0.128

From table 3 of SP 16,percentage of steel required/Minimum steel = Area of steel required =

0.12 650.40sqmm

Hence provide 12mm dia HYSD bars@ 150mm c/c spacing at bottom and provide 20mm bars at 110mm c/c at top

Hence Ast provided at top =

2854.55sqmm

Hence Ast provided at bottom =

753.60sqmm

Provide distribution reinforcement of 0.12% both at top and bottom Area =

720.00sqmm

Adopting 12mm dia bars,the spacing required is = Hence provide 12mm dia bars @ 150mm c/c spacing at top& bottom

157.00mm

Effective depth = 300-50-6 =

0.244m

Clear span between abutments = 3.00-2x(0.125+2x(0.15)) = Effective span = 2.15+0.244/2 =

2.150m 2.27m

For continuous slab,clear span will be the effective span,effective span = The raft is proposed to be designed for the Max.stress of 5.47t/sqm Assuming 1m width of raft,the UDL on the raft is

53.790t/Sqm

The raft is treated as simply supported beam with over hangs Hence,the Max.positive moment = wl2/8 =

34.71t-m

Max.Negative moment for over hangs = wl12/2 = Max.negative moment =

2.420t-m

Max.positive moment =

34.710t-m

Hence,the design moment =

34.710t-m

Depth required = 3.53x105 7.7x100

67.140094

2.42t-m

Hence provide overall depth of 30cm,the effective depth available is 300-50-6 =

24.4

Area of steel required = 3.53x105 at centre 2000x0.916x24.4

77.65sqcm

Spacing of 12mm dia bars required = 1.13x100/7.9 =

14.30379747

However provide 12mm bars at 125mm c/c at centre

Area of steel required = 0.25x105 for over hangs 2000x0.916x24.4

5.41sqcm

Spacing of 12mm dia bars required = 1.13x100/0.56 =

201.7857143

However provide 12mm bars at 250mm c/c Provide distribution reinforcement of 0.12% both at top and bottom Area =

3.60sqcm

Adopting 10mm dia bars,the spacing required is = 0.785x100/3.6 =

21.805556

Hence provide 10mm dia bars @ 175mm c/c spacing

The details of Reinforcement is as shown below:-

12mm bars@ 125 c/c(Curtail 50% of cranks at the centre of abutment

3.00m 12mm bars@250mm c/c

0.625 1.2 4.3 3 3 0.475

11.4 11.4 6.8 6.8 6.8

2.27m

1.1304

1.1304

0.785

12mm bars@250mm c/c

Hydraulic design Hydraulic Particulars:1.Full supply Level

1.477

2.Ordinary Flood level

------

3.Lowest Bed level

0.477

4.Average bed slope (1 in 17000)

0.000059

5.Rugosity Coefficient(n) (As per table 5 of IRC:SP 13)

0.020

6.Vertical clearence proposed (As per clause 15.5 of IRC:SP 13&as per profile)

0.510

6.Bottom of deck proposed (MFL+Vertical clearence)

1.987

7.Road Crest level (Bottom of deck level+thickness of deck slab)

2.577

8.Width of carriage way

5.500

Discharge Calculations:1)From the data furnished by the Irrigation Department:Design discharge =

2.074Cumecs

2)Area Velocity method:Depth of flow w.r.t HFL =

1.000m

Bed width =

4.50m

Assuming side slopes 1:1.5 in clayey soils,top width at HFL = Wetted Area =

6.000m

5.25sqm

Wetted perimetre =

7.33m

Hydraulic Radius

R=

Total area/Wetted perimeter =

Velocity V =

1/nX(R2/3XS1/2)

Discharge Q =

AXV

Design Discharge = Design Velocity =

Ventway Calculations(H.F.L Condition):-

0.72 0.31m/sec 1.63Cumecs 2.074Cumecs 0.31m/sec

Assuming the stream to be truly alluvial,the regime width is equal to linear waterway required for the drain. Hence,as per Lacey's silt theory,the regime width W = 4.8Q 1/2 = 4.8*2.0740.5 =

6.91m

The actual top width is almost equal to the above regime width.Hence,the stream is almost truly alluvial in nature. As per IRC:SP--13,the ventway calculations for alluvial streams are as given below:-

Assuming afflux = x = Width of channel at H.F.L(b+h) = Clear span = Effective linear water way = di = Depth of flow =

0.05m 6.00m 6.00m 6.00m 1.00m

Head due to velocity of approach =

(Vmax2/2g)X[di/(di+x)]2

0.004m

Combined head due to Velocity of approach and afflux

hi =

0.054m

Velocity through vents

0.90X(2ghi)1/2 =

Vv =

Linear water way required

LWW = Qd/(VvXdi) =

No.of vents required =

LWW /LC

0.93m/sec 2.24m

=

0.373333333 Say---1 Vent

In alluvial streams,the actual width of the stream should not be reduced,as it results in enhanced scour depth and expensive training works. Hence No.of vents required as per the width of the stream at H.F.L= (6/6.00) No.of vents to be provided

1 1Nos

No.of piers =

0Nos

Scour Depth Calculations:As per the clause 101.1.2 of IRC:5--1985,the design discharge should be increased by 30% to ensure adequate margin of safety for foundations and protection works Hence,the discharge for design of foundations = 1.30XDesign Discharge =

Lacey's Silt factor ' f ' = 1.76Xm1/2(For normal silt) = Discharge per metre width of foundations = q =

Normal scour depth D = 1.34(q2/f)1/3 =

Maximum scour depth Dm = 1.5XD =

Depth of foundation = Dm + Max.of 1.2m or 1/3 Dm =

Bottom level of foundation =

Depth of foundation below low bed level = The Minimum Safe Bearing capacity of the soil is considered as 65 KN/m2 at a depth of 1.50m below LBL Hence open foundation in the form of raft is proposed at a depth of 1.85m below LBL,ie,at a level of Cut-off walls and aprons are not required from scour depth point of view

s almost truly alluvial in nature.

s in enhanced scour

d by 30% to ensure adequate

2.76Cumecs

1.00 0.46

0.80m

1.20m

2.40m

-0.923m

1.400m

1.50m below LBL -0.923m