87. 74
Hydraulic Calculation for spillways
Width of spillways: B =
ππππ₯
πππ₯π»0π₯β2π
π
Cd = coefficient of discharge (C=0.6, 0.67)
K = pier Construction coefficient (k=1) ,
g= gravity acceleration g=9.81m/sec2
H0 = Total head on crest (H0 = βπ» +
ππ£02
2π
)
βπ»= design head m
a = Karialos coefficient (a = 1.05) V0 = water velocity over
spillway crest (1-2 m/s)
v0= 1.5m/sec βπ»= 2m
H0 = 2+
1.05π₯1.52
2π₯9.81
= 2.12π, Qmax= 360m3/sec
B =
360
0.65π₯1π₯2.123/2 π₯β2π₯9.81
= 40.5 π ππ¦ 41π
Now we can find width of every span by equation:
B = n*I + (n-1) *bp (m)
n= number of span (n=5)
I= width of span
bp= width of pier (2-3m) accept bp=2.5m
41= 5xI+(5-1) x2.5, I = 6.2 say 6.5m
B = 5x6.5+ (5-1) x2.5 = 42.5
89. 76
Hydraulic calculation for top and bottom of
spillway
Discharge per meter width of spillway crest:
q = cv x h1 x β2π₯π( π»0 + π) β β1 m3/sec x m
cv= coefficient of velocity (0.85-0.95) accept cv=0.9
P = height of spillway (p=29m)
q = 9.81
h1 = first hydraulic jump, also q= Qmax/B => 360/42.5 =
8.47 m3/sec2
Now we can find h1 from equation:
q = cv x h1 β2π₯π (π»0+ π) β β1 if
h1=0.5m=>q=0.9x0.45β2π₯9.81π₯(2.12 + 29) β 0.5
=11.11m2/sec
if h1=0.5m =>q = 0.9x0.45 β2π₯9.81(2.12 + 29) β 0.45
=10 m2/sec
if h1 = 0.4 => q = 0.9x0.4β2π₯9.81(2.12 + 29) β 0.4 =
8.89 m2/sec
if h1 = 0.39 => q = 0.9x0.39 β2π₯9.81(2.12 + 29) β 0.39
= 8.67 m2/sec
if h1 = 0.3818 => q = 8.488 m2/sec accept h1 = 0.381 m
Height of second hydraulic jumps:
h2 =
β1
2
β
1+8ππ2
πβ1
3 π =
0.381
2
β1 + 8 = 6.35π
90. 77
Length of stilling basin is finding from equation:
L = 5(h2-h1) => 5(6.35-0.381) = 29.8 m
91. 78
Shape of ogee β crest
1. Based on latest research of US corps up streams
curve is drawing by following formula:
ο§ Y =
0.724(π₯+0.27π»0)1.8
π»0
0.5 + 0.126 π»0 β
0.4315π»0
0.375
(π₯ + 0.27π»0)0.652
ο§ BY empirical formulas r1=0.5H0, r2=0.2H0, a=
0.175H0, b= 0.282H0
2. For drawing down stream curve we use the
following formulas:
ο§ X1.85 = 2H0
0.85y
For upstream curve: r1 =0.5x2.12= 1.06m, r2 =
0.2x2.12= 0.424, a = 0.175x2.12 = 0.371
b= 0.282x2.12 = 0.6
For downstream curve X1.85 = 2H0
0.85y => y =
π1.85
2π»00.85
X = 1m, y =
11.85
2π₯120.85 = 0.264m
X = 3m, y =
31.85
2π₯120.85 = 2.621m
X = 5m, y =
51.85
2π₯120.85 = 5.184m
X = 7m, y =
71.85
2π₯120.85 = 9.661m
X = 9m, y =
91.85
2π₯120.85 = 15.38m
X = 12m, y =
121.85
2π₯120.85 = 26.186m
X = 12.7m, y =
12.71.85
2π₯120.85 = 29.08m
97. 84
Stability Calculation for Spillway Cross Section
Gravity center of Spillway Section is calculation in Auto CAD easily.
Tools, inquiry, Region/mass, Properties
Area: 439.22m2
Perimeter: 108.21m
Centroid: X: 9.23m Y: 10.85m
Center of Gravity
98. 85
Forces acting on a Spillway:
1. Water pressure:
a) = External water pressure per length of spillway
p1 =
π€π₯(βπ»2)
2
T/m
w = Unit weight of water (w= 1000 kg/m3) =
1ton/m3
ΞH = Water head on spillway crest (ΞH = 2m)
P2=
π€π₯(βπ»2)
2
T/m =
1π₯(22)
2
= 2 ton/m
b) Water pressure β sensitive on spillway vertical
wall.
P3= wxΞHxH = 1x2x24 = 48 T/m
P4=
π€π₯π»π₯π»
2
=
1π₯24π₯24
2
= 288 T/m
2. Total pressure on vertical wall:
99. 86
P = p2 +p3 = 48 + 288 = 336 T/m
Position of resultant pressure:
Depth of the point of the resultant pressure from
base is calculating by taking moment of both the
pressure about point A and equation the source>
Pxh = (p2 x H/2) + (p3 x H/3) => 336xh = (48 x 24/2)
+ (288 x 24/3)
336h = 2880, h = 8.57m
3. Water pressure bellow the base of spillways or
uplift pressure:
P =
π€π₯π»π₯π
2
T/m => Puplift =
1π₯24π₯27.48
2
= 329.76 ton/m
100. 87
4. Psoil =
1
2
8h2 1βπ πππ
1+π πππ
t/m
h = the height of the silt is depositor (h = 2)
πΎ = the submerged unit of silt (1.2 t/m)
Q = the angle of internal fraction (π = 15 π
)
Psoil =
1
2
8h2 1βπ ππ15
1+π ππ15
= 28.62 t/m
5. Self-weight of spillway:
The weight of the dam is major resisting force for
analysis purpose, generally unit length of the dam
is considered.
G = A x r x 1m t/m, G = weight of spillways
A = spillways cross section Area
r = unit weight of spillway marital
A = 439.22 m2
G = 439.22 x 2.7 x 1 = 1185.89 t/m
G = G β Puplift = 1185.89 β 329.76 = 856.13 t/m
Ptotal = P(p2+p3) + Psoil = 336+28.62 = 364.62 t/m
Safety calculation for spillways:
R = β(πΊ12) + (ππ‘ππ‘ππ)2 = β856.132 + 364.622 = 930.54
t/m
TanΞ± =
π π‘ππ‘ππ
πΊ1
=
364.62
856.13
= 1.42589, Ξ± = 23.17o
B β€
π΅
6
b =
ππ₯πβ²
πΊ1
=
364.62 π₯ 10.85
856.13
= 4.62 say b = 4.6209
101. 88
π΅
6
=
27.76
6
= 4.6267
b β€
π΅
6
, b = 4.6209 < 4.6267 0k
Resultant line calculation for Rotation taking moment at
point C :
Mc = p(p2+p3) x
π»
2
+ psoil x
π» π πππ
3
+ psoil x
π΅
3
Mc = 336 x
33
2
+ 28.62 x
9
3
+ 329.76 x
27.76
3
Mc = 8681.24 T*m
Mcβ = G1 x Xβ = 856.13 x 9.23 = 7912.1
T*m
ππ
ππβ²
=
8681
7902
= 1.1 β₯ 1.1 safe against
overturning.
Calculation for slipper or sliding:
πΊ1
π π‘ππ‘ππ
x n =
856.13
364.62
x 0.7 = 1.644 > 1.1 ok
Safe against sliding
n = righty coefficient of material
102. 89
Design of Barge
Slab Design
LL = 60 T/m2
L = 1.4
h = 25 cm
self-weight of slab = 0.25 x 24 = 0.6 T/m2
self-weight of pcc = 0.2 x 2.9 = 0.44 T/m2
Total = 1.04 T/m2
Qu = 1.2 (1.04) + 1.6 (60) = 97.24 T/m2
Wu = 97.248 T/m per 1m strip
Wu = 97.248 x 1.4 = 136.2 T/m, b = 1.4
-veMo =
π€πΏ2
β24
=
136.2 π₯ 1.42
24
= 11.123 T x m = 109.1 KN.m
-veMo =
π€πΏ2
10
=
136.2 π₯ 1.42
10
= 261.7 Txm = 261.84 KN.m
+veMo =
π€πΏ2
14
=
136.2 π₯ 1.42
14
= 19.1 T x m = 187.31 KN xm
Note: negative moment at face of all support for a slabs with
spans not exceeding 10 ft moment is
π€π2
12
From Table 14.1 ACI coefficients
Design for 11.123 T x m = 109.1 KN x m
Rn =
ππ’
β ππ2
=
109.1 π₯ 106
0.9 π₯ 1000 π₯ 2202
= 2.505 mpa
π =
0.85 π₯ πΉβ²π
ππ¦
( 1 - β1 β
2π π
0.85 π₯ πΉβ²π
)
π =
0.85 π₯ 28
420
( 1 - β1 β
2 π₯ 2.2505
0.85 π₯ 28
) = 0.00632
As = πbd = 0.00632 x 1000 x 220 = 1390.4 m2
/sec
Trial and error Method:
β Mn = β Asfy (d-a/2)
103. 90
Mn = Asfy (d β a/2)
Req As =
ππ’
β ππ¦ (πβ
π
2
)
Assume z = 0.9d
First trial
Z = 0.9 x (22) = 19.8 cm
As =
109.1 π₯ 106
0.9 π₯ 420 π₯
= 1457.7 mm2
a =
1457.7 π₯ 420
0.85 π₯ 28 1000
= 25.724mm
z = d -
π
2
= 220 -
25.724
2
= 207.138 mm
2nd
trial:
Z = 207.138 mm
As =
109.1 π₯ 106
0.9 π₯ 420 π₯ 207.138
= 1393.39 mm2
a =
1393.39 π₯ 420
0.85 π₯ 28 1000
= 24.589 mm
z = 220 -
24.589
2
= 207.71
3rd
trail:
Z = 207.71
As =
109.1 π₯ 106
0.9 π₯ 420 π₯ 207.71
= 1389.55 mm2
closed
Req As = 1390 mm2
Try 14β mm
Ab =
ππ2
4
=
π π₯ 142
4
= 153.86 mm2
N =
1390
153.86
= 9.03 say 10
S =
π΄π
π ππ π΄π
π₯ 1000
104. 91
As = 9 x 153.86 = 1538.6
S =
153.86
1538.6
π₯ 1000 = 1000mm
β Mn = β Asfy ( d β a/2 )
a =
π΄π ππ¦
0.85 πΉβ² π π
=
1538.6 π₯ 420
0.85 π₯ 28 1000
= 27.15 mm
βt =
πβπ
π
x (0.003) > 0.005 Tension control
C =
π
π½1
=
27.15
0.85
= 31.94
βt =
220β31.
31.94
x (0.003) =0.0176 tension control
β Mn = 0.9 x 1588.6 x 420 (220 -
27.15
2
)
β Mn = 120054880.9 = 120.1 KN .m > 109.1 KN*M ok
Design for 26.7 T x m = 261.84 KN x m
Rn =
ππ’
β ππ2
=
261.84 π₯ 106
0.9 π₯ 1000 π₯ 2202
= 6.01
π =
0.85 π₯ πΉβ²π
ππ¦
( 1 - β1 β
2π π
0.85 π₯ πΉβ²π
) =
0.85 π₯ 28
ππ¦420
( 1 - β1 β
2 π₯ 6.011
0.85 π₯ 28
) =
0.0168
As = πbd = 0.0168 x 1000 x 220 = 3696 mm2
Trial and Error method:
β Mn = β Asfy (d-a/2)
Mn = β Asfy (d-a/2)
Req As =
ππ’
β ππ¦ (πβ
π
2
)
Assume
Z = 0.9 d
a = 0.9 x 220 = 198 mm
first trial:
105. 92
As =
201.84 π₯ 106
0.9 π₯ 420 π₯ 198
= 3498.48 mm2
a =
3498.48π₯ 420
0.85 π₯ 28 1000
= 61.74mm
z = d -
π
2
= 220 -
61.74
2
= 189.13 mm
2nd
trail:
As =
261.84 π₯ 106
0.9 π₯ 420 π₯189.13
= 3662.55 mm2
a =
3662.55π₯ 420
0.85 π₯ 28 1000
= 64.62 mm
z = d -
π
2
= 220 -
64.62
2
= 187.69 mm
3rd
trail:
As =
261.84 π₯ 106
0.9 π₯ 420 π₯ 187.69
= 3690.65 mm2
a =
3690.65 π₯ 420
0.85 π₯ 28 1000
= 65.13 mm
z = d -
π
2
= 220 -
65.13
2
= 187.435 mm
4TH
trail:
As =
261.84 π₯ 106
0.9 π₯ 420 π₯ 187.435
= 3695.67 mm2
a =
3695.67 π₯ 420
0.85 π₯ 28 1000
= 65.22mm
z = d -
π
2
= 220 -
65.22
2
= 187.39 mm
5th
trial:
As =
261.54 π₯ 106
0.9 π₯ 420 π₯ 187.39
= 3696.56 mm2
Req As = 3700mm2
Try β 32 mm
Ab =
ππ2
4
=
π322
4
= 804.25 mm2
106. 93
S =
π΄π
π ππ π΄π π₯ 1000
=
804.25
3700
= 217.36 mm say 200 mm
β Mn = β Asfy ( d β a/2 )
200 1
1000 X
X=5
As = 5 x 804.25 = 4021.25 mm2
a =
4021π₯ 420
0.85 π₯ 28 1000
= 70.96 mm
βt =
πβπ
π
x (0.003) > 0.005 Tension control
C =
π
π½1
=
70.96
0.85
= 83.48
βt =
220β83.48.
83.48
x (0.003) = 0.005 tension control
β Mn = 0.9 x 4021 x 420 (220 -
70.96
2
) = 280458959.8 N.mm =
280.46 KN.m > 261.84 0k
Design for positive moment:
Mo = 19.7 Txm = 187.3 kn.m
Rn =
ππ’
β ππ2
=
187.3 π₯ 106
0.9 π₯ 1000 π₯ 2202
= 4.3
π =
0.85 π₯ πΉβ²π
ππ¦
( 1 - β1 β
2π π
0.85 π₯ πΉβ²π
) =
0.85π₯ 28
420
( 1 - β1 β
2 π₯ 4.3
0.85 π₯ 28
) =
0.0114
Trial and error method:
β Mn = β Asfy (d-a/2)
Mn = β Asfy (d-a/2)
Req As =
ππ’
β ππ¦ (πβ
π
2
)
Assume
107. 94
Z = 0.9 d
a = 0.9 x 220 = 198 mm
first trial:
As =
187.3 π₯ 106
0.9 π₯ 420 π₯ 198
= 2502.54 mm2
a =
2502.54π₯ 420
0.85 π₯ 28 1000
= 44.162mm
z = d -
π
2
= 220 -
44.162
2
= 197.919 mm
2nd
trail:
As =
187.3 π₯ 106
0.9 π₯ 420 π₯197.919
= 2503.56 mm2
Req As = 2504 mm2
Try 250 mm
Ab =
ππ2
4
=
π252
4
= 490.87 mm2
S =
π΄π
π ππ π΄π π₯ 1000
=
490.87
2504 π₯ 1000
= 196.03 say 200mm
N = 5 from table B4
As = 2550 mm2
a =
2550 π₯ 420
0.85 π₯ 28 1000
= 45 mm
C = 45/0.85 = 52.94
βt =
220β52.94.
52.94
x (0.003) = 0.0095 > 0.005 Tension control
β Mn = 0.9 x 2550 x 420 (220 -
45
2
) = 190.37 KN . m > 187.84 OK
Shrinkage Reinforcement:
Try 100mm, Ab = 78.54
Req As = πbd = 0.00181 x 1000 x 220 = 398.2 m
S =
π΄π
π ππ π΄π π₯ 1000
=
78.54
398.2 π₯ 1000
= 197.2 say 190
108. 95
S = 165mm, As = 430 mm2
ok
Design of Beam
Mu =
π€πΏ2
8
=
136.2 π₯ 8.52
8
= 1230 T*m = 12062.2 KN*m
110. 97
Mn2 = Mn - Mn1 = 13402.44 β 11042.1 = 2360.34 Kn.m
Mn =
12062.2
0.9
= 13402.49
Checking to see compression steel yields:
a =
20020 π₯ 420
0.85 π₯ 35 π₯ 700
= 403.76
C =
π
π½1
=
403.76
0.814
= 496.025 from table B7 B= 0.81 , fβc = 35
Es =
496.025β70
496.025
x (0.003) = 0.00256 >
420
2000 πππ
= 0.002
Compression steel yields
Asβ Req =
ππ2
ππ¦ (πβπβ²)
=
2360.34 π₯ 106
420 (1430β70)
= 4132.25 mm2
Use 7 # 29 mm bars (4515) spicin 100mm
As = As1 + As2 = 20020 + 4132.25 = 24152.25
Use 10# 57 bar (25810) spicing 70 mm
111. 98
Checked
As1 = As β As2
As = 25810 mm2
As2 = 4515 mm2
As1 = 25810 β 4515 = 21295 mm2
Fs = fy
a =
21295 π₯ 420
0.85 π₯ 35 π₯ 700
= 429.479 mm
c =
429.479
0.814
= 527.615 mm
Es = =
527.615β70
527.615
x (0.003) = 0.0026 > 0.0021
Fy =fs, As2 = As
Mn1 = As1fy (d β a/2) = 21295 x 420 (1430 -
429.48
2
) = 10869.16
Kn.m
Mn2 = As2fy (d-dβ) = 4515 x 421nx (1431 β 70) = 2578.92 Kn.m
Mn = Mn1 + Mn2 = 10869.16 + 2578.97 = 13448.128 KN.m
βt =
πβπ
π
x 0.003 =
1430β527.615
527.615
x 0.003 = 0.00513 > 0.005 tension
control
β Mn = 0.9 x 13448.128 = 12103.31 > Mu = 12062.2 OK
112. 99
Design of Beam for shear
VA = VB =
ππ
2
=
136.2 π₯ 8.5
2
= 518.85 T = 5676.58 KN
Fβc = 35
Fy = 420
d = 1430 mm = 1.43 m
5676.58
4.25
=
ππ’
(4.25β1.43)
Vu = 3766.6 Kn
β vc =
β βπΉβ² π π ππ€ π₯ π
6
=
0.75 β35 π₯ 700 π₯ 1430
6
= 740.249 KN
Vs =
ππ’β β ππ
β
=
3766.6β740.25
0.75
= 4035.133 KN
Use 19β mm
Av = 283.53 mm2
S =
π΄π£ π₯ πΉπ¦π
ππ
=
283.53 π₯ 420 π₯ 1430
4035.133
= 42.2 mm
113. 100
Smax =
3π΄π£ π₯ πΉπ¦
ππ€
=
3 π₯ 283.53 π₯ 420
700
= 510 mm
1. If VS < 1/3 βπΉβ²πππ€π
Smax = d/2
2. VS > 1/3 βπΉβ²πππ€π
Smax = d/4
3. VS > 2/3 βπΉβ²πππ€π
Not good
1/3 β35 π₯ 700 π₯ 1430 =1974 KN < Vs
2/3β35 x 700 x 1430 = 3948 KN < Vs
If we change d to up 1460 then its ok but
now we accepted this ok
The d/4 = 1430/4 = 357.5
S = 42mm
Av 283.53
Fy 420
Fc 35
Bw 700
d 1430
Vu 5676.58
L 4.25
oVc 740.249
Distance 1.43 1.5 1.6 1.7 1.8 1.9 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6
Vu 3767 3673 3540 3406 3272 3139 3005 2738 2471 2204 1937 1670 1402 1135 868
Vs 4035 3910 3732 3554 3376 3198 3020 2664 2308 1951 1595 1239 883 527 171
S 42 44 46 48 50 53 56 64 74 87 107 137 193 323 998
Smax 510 510 510 510 510 510 510 510 510 510 510 510 510 510 510
1 con 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974
2 con 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974
3 con 3948 3948 3948 3948 3948 3948 3948 3948 3948 3948 3948 3948 3948 3948 3948
Spacing 42 44 46 48 50 53 56 64 74 87 107 137 193 323 715
Design for shear with deferent distance
114. 101
B = (1.25 Γ· 1.75) H
B = (1.75 Γ· 2) H
B = (2 Γ· 2.25) H
B = (2 Γ· 2.5) H
π΅
π»1
= m
π΅
π»1
=
1
β
πΎπ
πΎπ€
βπ
H = 32m
πΎπ= (2.3 β 2.4) T/m3
πΎπ€ = 1.0 T/m3
π΅
π»1
= m => B = m x H1 = 0.7 x 32 = 22.4
π΅
π»1
=
1
β
πΎπ
πΎπ€
βπ
=
32
β
2.4
1
β0.7
, B = 24.5 say 25m
b = 7m, ΞH = 3m
X =
π» π₯ π
π΅
=
32 π₯ 7
25
= 9m
H5 = H4 + ΞH = 9 + 3 = 12m
115. 102
Force acting on a Dam:
1. Water pressure:
2. Uplift pressure
3. Pressure date earthquake force
4. Silt pressure
5. Wave pressure
6. Ice pressure
7. The stabilising force is the weight of the dam itself>
Water pressure:
P1 = Β½ πΎπ€ H2
P1 = Β½ x 1 x 322
= 512 T/m
P4 = Β½ x 1 x 2.52
= 3.125 T/m
117. 104
Wave pressure:
Waves are generated on the surface of the reservoir by
the blowing winds, which causes a pressure towards the
downstream side. Wave pressure depends upon the wave
height. Wave height may be given by the equation,
Pw =
1
2
(2.9 πΎπ€ hw)
5
3
hw
Pw = 2 πΎπ€ hw2
hw = 0.032 β π. πΉ + 0.763 β 0.271 (F)3/4
, F<32km
hw = 0.032 β π. πΉ for F > 32 km
hw = height of water from top of crest to bottom of trough
in meters
V = wind velocity in Km/hr
F = fetch or straight length of water expanse in km
V = 124 km/hr
F = 7km
hw = ?
hw = 0.032 β124 + 0.763 β 0.271(73/4)
hw = 1.75 β 1.167 = 0.543m
pw = 2 x πΎ x hw2
= 2x 1 x 0.5432
= 0.6 T/m
3/8 x 0.543 = 0.204m
Aram = 32 + 0.204 = 32.204
Moment = 19.32 T*m
118. 105
Ice pressure:
The ice which may be formed on the water surface of the reservoir
in cold countries, may sometimes melt and expand. The dam face
has then to resist the thrust exerted by the expanding ice. This force
acts linearly along the length of the dam and at the reservoir level.
The magnitude of this force varies from 250 to 1500 kN/m 2
depending upon temperature variations. On an average, a value of
500 kN/m 2
may be allowed under ordinary conditions.
Earth quake pressure:
If the dam to be designed, is to be located in a region which
is susceptible to earthquakes, allowance must be made for
the stresses generated by the earthquakes.
An earthquake produces waves which are capable of shaking
the Earth upo~ which the dam is resting, in every possible
direction.
The effect of an earthquake is, therefore, equivalent to
imparting an acceleration to. the foundations of the dam iri the
direction in which the wave is travelling at the moment. Earthquake
wave may move in any direction, and for design purposes, it has to
be resolved in vertical and horizontal components. Hence, two
accelerations, i.e. one horizontal acceleration (ah) and one vertical
acceleration (av) are induced by an
earthquake. The values of these accelerations are generally
expressed as percentage of the acceleration due Β·tO gravity (g} πΌ =
0.1π ππ 0.2π ππ‘π
ln India, the entire country has been divided into five seismic
zones depending upon the severity of the earthquakes. Zone Vis
the most serious zone and includes Himalayan regions of NortJ::i
India. A map and description of theseΒ·zones is available in
"Physical and Engineering Geology" (1999 edition) by the same
author, and can be referred to, in order to obtain an idea of the value
of the a which should be chosen for designs. On an average, a value
of a equal to 0.1 to 0. 15 g is generally sufficient for high daqs in
seismic zones. A vaiue equal to 0.15 g has been used in ~hakra
dam design, and 0.2 g in Ramganga -dam design. However, for
areas not subjected to extreme earthquakes,
119. 106
πΌβ = 0.1 g and πΌ π£ = 0.05 g may by used. In areas
of no earthquakes
or very
less
earthquakes, these forces may be neglected. In extremely
seismic regions and in con-servative designs, even a value upto
0.3 _g may sometimes be adopted. -
Effect of vertical acceleration (CXy). A vertical acceleration
may either act downward or upward. When it is acting in the
upward direction, then the foundation of the dam will be lifted
upward and becomes closer to the body of the dam, and thus the
effective weight of the dam will increase and hence, the ~tress
developed will increase.
When the vertical acceleration is acting downward, the
foundation shall try to move downward away from the dam
body ; thus reducing the effective weight and the stability of the
dam, and hence is the worst case for designs .
Such acceleration will, therefore, exert an inertia force
given by
π
π
πΌ π£ (i.e. force= Mass x Acceleration)
where W is the total weight of the
darn.
:. The net effective weight of the dam=
π β
π
π
πΌ π£
If
where kv is the fraction of gravity
adopted for ver-tical acceler-at:ion,
such as 0.1 or 0.2, etc.].
Then, the net effective weight of the darn
120. 107
In other words, vertical acceleration reduces the unit
weight of the darn material and that of water to (I - ky) times
their original unit weights.
Effect at vertical acceleration:
av = Kv*g
Kv = is the fraction of gravity adopted for vertical
acceleration such as 0.1 or 0.2 ok
w/g*av
The net effect weight of dam = w
π€
π
av => w
π€
π
kv = w [1-kv]
Av = 0.2 x 1 = 0.2 t/sec
Effect of horizontal acceleration:
ah = horizontal acceleration may cause the following two
force:
I. Hydrodynamic pressure
II. Horizontal inert force
A. Hydrodynamic pressure:
Pe = 0.555 KN rw H2
If act at the height of 4H/3π above the base where kh is
the fraction at gravity adopted for horizontal , such 0.1 ,
1.2 etcβ¦
πΎπ€ = unit weight of water
ππππππ‘ ππ π‘βππ ππππππ :
121. 108
Mc = pe
4π»
3π
= 0.424 pe *H
Zanger formula:
Zanger.has given certain-big.formulas for evaluating
theamoi.mLoLthis force and_ itsΒ· position, etc. on the
vertical as well as on an inclined faces. The results of these
big formulas are quite comparable to those given by Von-
Karman equation and hence, for average ordinary purposes,
the Von-Karman equation (19.1) is sufficient.
Zanger's formula for hydrodynamic force. According to
Zanger
Pe= 0.726pe Β· H
where Pe =-Cm KN Β· Yw Β· H
Pe= 0.726 Cm. kh. Yw. H2
Pe = 0.555 x 0.1 x 1 x 322
= 56.83 T/m
Me= 0.299 PeΒ·
H2
or
Me=0.412Pe
Β·H
Me = 56.83 (
4π₯32
3π
) = 771.1 txm
Silt pressure:
It has been explained under 'Reservoir Sedimentation' in
chapter 18 that silt gets deposited against the upstream face of
the dam. If his the height of silt Β· deposited, then the force
exerted by this silt in addition to external water pressure, can
be represented by Rankine's formula
as : Β· -
122. 109
Psilt =
1
2
πΎπ π’π π₯ β2
ππ
And its acts at h/3 from base:
Ka = is the coefficient at active earth pressure of silt =
1βπ πππ
1+π πππ
where π is the angles at internal fraction of soil, and
cohesion is neglected.
πΎπ ππ = submerged unit weight of salt material
h = height of silt deposited
unit wt equal to 3.6 KN/m3
for horizontal direction and
vertical 9.2 KN/m3
the total horizontal force will be 1.8h2
KN/m
1.8 KN/m = 0.184 T/m, 4.6 KN/m = 0.469 T/m
123. 110
No Name of the force Symbol
Deminsion
(m)
Area
(m2
)
Ξ΄w
(T)
F (T)
Downword=+ve,
Upword =-ve
Arm
(m)
Moment
(T*m)
1 W1 7*35 245 2.7 661.5 21.5 14222.25
2 W2 (18*26)/2 234 2.7 631.8 12 7581.6
βV1,βM1 1293.3 21803.85
3 weight of Water W3 (1.73*2.5)/2 2.1625 1 2.1625 0.5767 1.247041667
βV2,βM2 2.1625 1.247041667
4 U1 (-)25*2.5 -62.5 1 -62.5 12.5 -781.25
5 U2 (-)(25*29.5)/2 -245.8 1 -245.8333333 16.667 -4097.222222
βV3,βM3 -308.3333333 -4878.472222
6 P1 (32*32)/2 -341.3 1 -341.3333333 10.667 -3640.888889
7 P2 (1.73*2.5)/3 1.0813 1 1.08125 1.6667 1.802083333
βH1,βM4 -340.2520833 -3639.086806
8 Wave pressure P(wave) 1 -0.6 32.204 -19.3224
βH2,βM5 -0.6 -19.3224
9
Upword vertical
earthquak force (-)1.15*βV1 -64.665 -109.01925
βV4,βM6 -64.665 -109.01925
10
Horizontal
hydrodynamic
pressure pe -56.83 -771.1
βH3,βM7 -56.83 -771.1
11 (-)0.1*W1 -66.15 17.5 -1157.625
12 (-)0.1*W2 -63.18 8.6667 -547.56
13 βH4,βM8 -129.33 -1705.185
Uplift force
Horizontal
hydrostatic pressure
weight of dam
Horizantal inertia
force due to
earthquak
total moments 10682.91136
total of vertical force 922.4641667
Total of positive moment 21805.09704
total of nagitive moment -11122.18568
Total of horzoantal forces -527.0120833
124. 111
Checking
Combination of forces for Designs. The design of a gravity
dam should be checked for two cases, i.e. (i) when Reservoir is
full; and (ii) when Reservoir is empty.
Case I. Reservoir full case:
When reservoir is full, the m~jor forces acting are: weight of
the dam, external water pressure, uplift pressure, and
earthquake forces in serious seismic zones. The minor forces are:
silt pressure, ice pressure and wave pressure. For the most
conserva-tive designs, and from purely theoretical point of view,
one can say that a situation may arise when all the forces may act
together. But such a situation will never arise and hence, all the
forces are not generally taken together. U.S.B.R. has classified the
'normal load combinations' and 'extreme load combination, as
given below:
(a) Normal Load Combinations
(i) Water pressure upto normal pool level, normal uplift, silt
pressure and ice pressure. This class of loading is taken when ice
force is serious.
(ii)Water pressure upto normal pool level, normal uplift,
earthquake force. s, and silt pressure.
(iii)Water pressure upto maximum reservoir level (maximum
pool level), normal uplift, and silt pressure.
(b)Extreme Load Combinations
(i)Water pressure due to maximum pool levcl, extreme uplift
pressure witho_ut any
reduction due to drainage and silt pressure. -
125. 112
Case II. Reservoir empty case :
(i)- Empty rese-rvo1r - w-ithout eartlicfuake- fotce-s-ro-be-
computed-for-determining-bending diagrams, etc. for
reinforcement design, for grouting studies or other puiyoses.
(ii) Empty reservoir with a horizontal earthquake force
produced towards the
upstream has to be checked for non- development of tension at
toe.
Modes of Failure and Criteria for Structural Stability of
Gravity Dams A gravity dam may fail in the following
ways:
(1) By overturning (or rotation) about the toe
(2} By crushing.
(3) By development of tension, causing ultimate failure
by crushing.
( 4) By shear failure called sliding.
The failure may occur at the foundation plane (i.e. at the base
of the dam) or at any other plane at higher level.
(lj Over-turning. If the resultant of all the- forces acting on a
dam at any of its sections, passes outside the toe, the dam shall
rotate and overturn about the toe. Practi-cally, such a condition
shall not arise, as the dam will fail much earlier by compression.
The ratio of the righting moments about toe (anti clockwise) to
the over turning moments about toe (clock-wise) is called the
factor of safety against overturning. Its value, generally varies
between 2 to 3.
126. 113
(2)Compression or crushing. A dam may fail by the failure of its materials, i.e.
the compressive stresses produced may exceed the allowable stresses, and the
dam-material may get crushed. The vertical direct stress distribution at the
baseis given by the equation:
Pmax/min =
β π£
π΅
(1 Β±
6π
π΅
)
Note. Resultant is nearer theΒ· toe and hence,
maximum compressive stress is produced at the toe
127. 114
(Reservoir full case)
Not.,, The resultant is nearer the heel and
hence,
maximum compressive stress (+ve stress)
is
produced at the heel (Reservoir empty
with
horizontal earthquake wave moving away
from
reservoir-case).
If Pmin comes out to be negative, it means that tension shall be produced
at the appropriate end.
If Pmin exceeds the allowable compressive stress of dam material
[generally taken as 3000kN/m2
(30 kg/cm2
) for concrete]; the dam may crush
and fail by crushing.
Case 1. Reservoir Empty:
β π = Moment due to weight or dam M1+ due to horizontal earthquake
force moment due to vertical earth quack force.
β π = M1 + M2 +M3
β π = 21803.85 + 1705.185 +109 = 23618 Txm
β π£ = β π£ 1 + β π£ 4
β π£ = 1293.3 + 64.665 = 1357.965 T/m
Case 1. Reservoir empty and vertical earthquake force acting down word.
128. 115
When the reservoir is empty, the only single force acting on it is the self-
weight CW) of the dam and it acts at a distance B/3 from the heel. This is the
maximum possible innermost position of the resultant for no tension to
develop. Hence, such a line of action of Wis the most ideal, as it gives the
maximum possible stabilising moment about the toe without causing tension at
toe, when the reservoir is empty. The vertical stress distribution at the base,
when the reservoir is empty, is given as:
Xβ =
β π
β π£
=
23618
1357.965
= 17.39m
e =
π΅
2
β Xβ =
25
2
β 17.39 = -4.89m >
π΅
2
< 4.1667 m
Resultant acts near the heel and slight tension will be develop at toe
Pmax/min =
β π£
π΅
(1 Β±
6π
π΅
) =
1357.965
25
(1 Β±
6 π₯ 489
25
) = 54.32 ( 1Β± 1.174 )
Pmax = 118.1
Pmin =-9.45
Pv at heel = 118.1 T/m2
= 1158.165 KN/m β€ 3000 (safe)
The allowable compressive stress of dam material:
(generally taken as 3000 KN/m2
= 306 T/m2
for concrete)
R at toe = -9.45 T/m2
= -92.67 KN/m2
< 420 (safe)
420 KN = 42.82 T
Average vertical stress:
β π£
π΅
=
1357.965
25
= 54.32 T/m2
< 306 t/m2
(safe)
Principle stress at toe
π = pv(heel) sec2
π
π = 48.1 = 118 T/m2
< 306 (safe)
Shear stress at toe
To (toe) = p toe tanΞ±
To(toe) = -9.45 x 0.7 = -6.615 < 42.82 (safe)
Shear stress at heel
β 0 (heel) = Pv (heel) tanπ
To (heel) = 1357.965 x 0 = 0 < 306 (safe)
Case 1. (b) Reservoir empty and vertical earthquake force are acting up
word.
Then β π£ = β π£ 1 - β π£ 4
129. 116
β π£ =1293.3 β 64.665 = 1228.635 T/m
β π = β π 1 + β π 8 - β π 6
β π = 21803.85 + 1705.185 β 109 = 23400.035 Txm
Xβ =
β π
β π£
=
23400.035
1228.635
= 19.05 m
e =
π΅
2
β xβ =>
25
2
β 19.05 = -6.55m
e = -6.55 <
π΅
6
= 4.167
Negative sign shows that resultant lies near heel and therefore, tension
will develop at toe
Average vertical stress:
β π£
π΅
=
1228.635
25
= 49.14 < 306 (safe)
Pmax/min =
β π£
π΅
(1Β±
6π
π΅
)
Pmax/min =
1228.635
25
(1Β±1.572)
Pmax = Pv at heel = 49.14 x 2.572 = 126.39 < 306 (safe)
Pmin = Pv at toe = 49.14 x (0.572) = -28.11 < 42.82 (safe)
Principal stress act on toe
π = Pv (toe) tanΞ± = -28.11 x 0.7 = -19.68 < 42.82 (safe)
Shear stress act on toe:
= pv (toe) tanΞ± = -28.11 x 0.7 = -19.68 < 42.82 (safe)
Stresses at heel remain critical in this 1st case.
Case 2 when Reservoir is full:
Horizontal earthquake moving towards the reservoir causing
upstream acceleration,
and thus producing horizontal forces towards downstream is
considered, as it is the worst
case for this condition. Similarly, a vertical earthquake moving
downward and thus,
130. 117
producing forces upward, i.e. subtractive to the weight of the dam
is considered.
The uplift coefficient C is taken as equal to 0.6, as given in the
equation, and thus
uplift pressure diagram as shown in Fig. 19.20 (c), is developed.
Case 2 (a) Reservoir full with all forces including uplift.
β π= β π 1 + β π 2 - β π 3 - β π 4 - β π 5 - β π 6 - β π7 - β π 8
β π = 21803.85 + 1.25 β 4878.5 β 19.32 β 109 β 771.1 β 1705.185 =
10683 Txm
β π£ = β π£ 1 + β π£ 2 - β π£ 3 - β π£ 4
β π£ = 1293.3 + 2.16 β 308.33 β 64.665 = 922.465 T/m
Xβ =
β π
β π£
10683
922.5
= 11.58 m
e =
π΅
2
β xβ =
25
2
β 11.58 = 0.92 <
π΅
6
= 4.1667
Average vertical stress:
β π£
π΅
=
922.5
25
= 36.9 T/m2
Pmax/min =
β π£
π΅
(1Β±
6π
π΅
) =
922.5
25
(1Β±
6 π₯ 0.92
25
) =36.9 x (1 Β± 0.2208)
Pmax = Pv (toe) = 36.9 x 1.2208 = 45.05 T/m < 306 (safe)
Pmin = Pv (heel) = 36.9 x 0.7792 = 28.75 T/m < 42.82 (safe)
P = πΎπ€ x H = 1 x32 = 32 T/m, Pβ= πΎπ€ x Hβ = 1x2.5 = 2.5 T/m
Principle stress at toe:
π = Pv(toe) x Sec2
Ξ± β Pβ tan2
Ξ±
π = 45.05 x (1+0.49) β 2.5 x 0.49 = 65.9 T/m2
< 306 T/m2
(safe)
Principle stress of heel is:
π1 = Pv (heel) sec2
π β (P + Pe) tan2
π, tan π = 0, Pe = 56.83 T/m
π1 = 28.75 x ( 1+ tan2
0) β (32 + 56.83) x tan (0)2
131. 118
π = 28.75 T/m2
< 42.82 T/m2
(safe)
Shear stress at toe
β 0 (toe) = (Pv(toe) β Pβ) tanΞ± = (45.05 β 2.5) x 0.7 = 29.785 T/m < 42.82
(safe)
Shear stress at heel:
β 0 (heel) = - (Pv(heel) β (P+Pe)tan π
β 0 (heel) = - (28.75) β (32 + 56.83) x tan0 = -28.75 < 306 T/m (safe)
Factor of safety against overturning:
=
β π (+)
β π (β)
=
21805.1
11122.18
= 1.96 > 1.5 (safe)
Factor of safety against sliding:
=
π β π£
β π»
=
0.7 π₯ 922.47
527.013
= 1.22 > 1 (safe)
Shear fraction factor:
S.F.F =
π β π£+π΅π
β π»
q = Average shear strength of the joint which varies from about 1400 KN
/m2
for poor rocks to
about 4000 KN/m2
for good rocks.
Β΅ = 0.15 β 0.75
S.F.F =
0.75 π₯ 922.46+25 π₯ 1400
527.013
= 3.93 >3 (safe)
Case 2 (b) Reservoir full, without up lift
Sometimes, values of stresses at toe and heel are worked out when
there is no uplift, as the vertical downward forces. is maximum in this case?
For this case, we shall calculate 2:M and I: V by ignoring' the corresponding
values of 2: V3 and 2:M3 caused by uplift.
β π = β π 1 + β π 2 - β π 4 - β π 5 - β π 6 - β π 7 - β π 8
β π = 21803.85 + 1.25 β 3639.086 β 19.32 β 109 β 771.1 β 1705.185
β π = 15561.41 T*m
152. 139
Design of Kaplan turbine
Q = 15 m3
/sec, H = 29.5 m, nh = 0.9, π = 998 kg/m3
, g = 9.81 m/sec2
Power and specific speed:
P= Q x H x nh x π x g
P = 15 x 29.5 x 0.9 x 998 x 9.81 = 3899018.835w => 3899kw => 3.9Mw
Specific speed:
NQE =
2.294
π»π0.486
H = Gross head
Hn = Net head
Hn = H x nh => 0.9 x 29.5 = 26.55m
NQE =
2.294
26.550.486
= 0.467
Rotational speed:
153. 140
NQE =
π π₯ βπ
πΈ3/4
=> n =
π ππΈ π₯ πΈ3/4
βπ
E = specific hydraulic anergy :
E = Hn x g = 26.55 x 9.81 = 260.45 J/kg
There for:
n =
0.467 π₯ 260.453/4
β15
= 7.82 5-1
= 469 Rpm
Run away speed:
The runaway speed is the max speed which the turbine can theoretically itβs
achieve during load reaction
The following guideline can be use to determine the runaway speed.
Turbine type Runaway speed max/n
Single regulated Kaplan turbine 2.0 β 2.6
Doled regulated Kaplan turbine 2.8 β 3.2
Choosing double regulated turbine
nmax = 3.2 x 7.82 = 25 5-1
Runner Diameter:
De = 84.5 x (0.79 + 1.602 x nQE) x
β π»
60 π₯ π
De = 84.5 x (0.79 + 1.602 x 0.467) x
β26.55
60 π₯ 7.82
= 1.43m
Hub Diameter:
Di = ( 0.25 +
0.0951
π ππΈ
) x De
Di = ( 0.25 +
0.0951
0.467
) x 1.43 = 0.65m
154. 141
Section head:
The section head, itβs the head where the turbine is installed it the section head
is positive the section head turbine is located above the trail water if the
section head is negative , the turbine is located under the trail water, to avoid
cavitation the range of the section head limited.
The maximum allowed section head can be calculated using the following
formula or equation:
Hs =
πππ‘ππβππ£
π π₯ π
+
πΆπ’2
2 π₯ π
β 6 x Hn
Where
Patom = atmospheric pressure (Pa)
Pv = water vaper pressure (Pv)
P = water density (kg/m3
)
g = acceleration of gravity
155. 142
Cu = outlet average velocity (m/sec)
π = Conation coefficient (-)
Hn = net head (m)
Patom = 101300 pu, Cu = 2m/sec
Pv = 2985.7 pa, Hn = 26.55m
π = 1.5241 x nQE
1.46
+
2
2 π₯ π π₯ π»π
π = 1.5241 x 0.4671.46
+
2
2 π₯ 9.81 π₯ 26.55
= 0.51
Hs =
101300β2985.7
998 π₯ 9.81
+
22
2 π₯ 9.81
β 0.51 x 26.55 = -3.29m
156. 143
Generator Design:
Number of poles
Np = 120 x F/N
Where
Np = Number of poles
F = frequency of supply ie 50 Hz in Afghanistan
N = Rotational speed (RPM)
Np = 120 x
50
469.2
= 12.79 β 13 poles
The table of standard rotational speed of Generator with explanation:
The ideal speed
= 1500 RPM1-
N = 25 5
Hence
Np = 120 x f/N => 120 x
50
1500
= 4 poles
Exciter of Generator
Explanation on page : 27
Type of exciter
1. Brush type
2. Brushless type
Explanation on page 27 β 28
Generator out put:
The output of generator is shown in VA and calculation following
Pg (KVA) = 9.81 x H x Q x q x P/Pf
Pg = required power output, KVA = kilo volt ampere.
H = net head
Q = design discharge
157. 144
Mo = over all efficiency is turbine efficiency transmission efficiency, nm x
generator efficiency.
π = density of water
PπΎ = power factor
Pg (KVA) =
9.81 π₯ 26.55 π₯ 15 π₯ 1000 π₯ 0.89/0.8
1000
= 4346.351 KVA
Speed Governor:
Explanation on page 28 β 29
Pd = pg x pt x s.f
Where
Pd = capacity of the dummy load
Pg = rated output of the generator
S.F = safety factor according the cooling method being employed (1.2 β 1.4)
Pd (KW) = 4.4MVA x 0.8 x 1.4 = 4.93 MW
Design at civil structure:
Penstock flow velocity = 4.5 m/sec
This is form exβ¦
Penstock rang (2m/s to 5m/s)
Find internal diameter
A = a/v =
15
4.5
= 3.33
Area of circle
A = πr2
=> A = πD2
/4
D2
= 4A/π => D = 2 x β
π΄
π
= 2 x β
3.33
π
= 2.1 m
Determination of the desntock thickness, tp
tp = p x πΎ/6
p = pn + ps
where
p = total pressure
158. 145
ph = pressure due to water hammer
ps = static water pressure
π = stress
Ph = πw x cp x v
Cp = for water under ordinary condition
Cp = 1120
Ph = 1000 x 1120 x 4.5 = 5.04 Mpa
Static pressure ps
Ps = πw x g x H
Ps = 1000 x 9,81 x 29.5 = 289395 = 0.2894 Mpa
Factor of safety n = 4
πgp = 957 Mpa
But
P = hn + ps = 5.04 + 0.2894 = 5.3294 Mpa
π Allowable = p/n = 957 x 106
/4
π Allowable = 239.25 Mpa
Hence
tp = P x πΎ/ π Allowable = =
5.3294 π₯ 106 π₯ (
21
2
)
239.25 π₯ 106
= 0.023389m
tp = 23.4 mm β 24 mm
Head losing penstock:
hv = K x V2
/2xg
But k = 0.2
hv =
0.2 π₯ 4.52
2 π₯ 9.81
= 0.2064 m
but two values lie at the entry and exct
hut = 2 x 0.2064 = 0.42 m
159. 146
head loss date bend, hb
hb = C x V2
/2g
for the deflection angle of 45 Co
= 0.09
hb =
0.09 π₯ 4.52
2 π₯ 9.81
= 0.093 m
head loss due to fraction hf
hf = f x (lp/Dp) x (V2
/2g)
f = π4/Re for Re β€ 2111 (laminar flow)
Re = VD/πΎ
f =
1.325
βln(
π
3.7π·
+
5.74
π π0.9)β2
for 5111 β€ Re β€ 118
and 10-6
β€ e/D β€ 11-2
(Turbulent flow)
hf = 0.009 x 150/2.1 x 4.52
/2x9.81 = 0.663
total head loss in the ht
ht = 0.42 + 0.093 + 0.663 = 1.987 β 2m
ht = 1.176m
Net head is 29.5 β 1.176 = 28.3m
For the design rule:
hl β€ 1.15 x 29.5 m
1.176 β€ 1.15 x 29.5
1.176 β€ 1.475
From the above rule head loss comply with it hence the design is safe.
161. 148
Estimation of penstock pipes
Internal Diameter Di = 21m
Lengh of penstock lp = 150m
Thickness tp = 24mm
Density of steel 8000 kg /m3
Price of steel = 50 Afg per kg
Volume of steel = π x lp (
π·π+2 π₯ π‘π
2
)2
β (
π·π
2
)2
V = π x 150 x (
2.1+2 π₯ 0.029
2
)2
β (
2.1
2
)2
= 24m3
Mass = density x voulume = 8000 x 24 = 192175 kg
Cost = (price/kg) (m)
Cost = 50 x 192975 = 1921750 Afg
1T = 60000 Af