irrigation

1. Gravity DamGravity Dam
A gravity dam is an engineering structureA gravity dam is an engineering structure
that by its own weight, resists the forcesthat by its own weight, resists the forces
imposed with a desired factor of safetyimposed with a desired factor of safety

2. Images of gravity damImages of gravity dam

3. Forces Acting on DamsForces Acting on Dams
To design a dam, various forces must beTo design a dam, various forces must be
considered to insure the safety of theconsidered to insure the safety of the
dam. The most important forces aredam. The most important forces are::
1.1. Weight of damWeight of dam
2.2. Water PressureWater Pressure
3.3. UpliftUplift
4.4. Wave pressureWave pressure
5.5. Earthquake forcesEarthquake forces

4. •A gravity dam is an engineering structure
that by its own weight, resists the forces
imposed with a desired factor of safety

5. • Weight of DamWeight of Dam
The weight of the dam is calculated asThe weight of the dam is calculated as
follows:follows:
WhereWhere γγmm is the specific weight of the dam’sis the specific weight of the dam’s
material.material.
xVolumeW mγ=

6. • Water PressureWater Pressure
Water pressure acts perpendicular to the surfaceWater pressure acts perpendicular to the surface
of the dam and is calculated per unit width asof the dam and is calculated per unit width as
follows:follows:
WhereWhere γγw is the specific weight of water and h isw is the specific weight of water and h is
the height of water.the height of water.
2
2
1
hP wγ= Pw
h/3
h

7. • UpliftUplift
Dams are subjected to uplift force under itsDams are subjected to uplift force under its
base. Uplift acts upward.base. Uplift acts upward.
Where B is the width of the base of the dam.Where B is the width of the base of the dam.
hBU wγ
2
1
=
h
U
B
B/3

8. • Wave PressureWave Pressure
The upper part of the dam (above the waterThe upper part of the dam (above the water
level) is subjected to the impact of waves.level) is subjected to the impact of waves.
The maximum wave pressure per unitThe maximum wave pressure per unit
width is:width is:
Where hWhere hww is the wave height.is the wave height.
vwv hP γ4.2=
Pw
0.375hw hw

9. Earthquake ForcesEarthquake Forces
Dams are subjected to vibration duringDams are subjected to vibration during
earthquakes. Vibration affects both theearthquakes. Vibration affects both the
body of the dam and the water in thebody of the dam and the water in the
reservoir behind the dam. Vibration forcesreservoir behind the dam. Vibration forces
are function of both the intensity (Rechterare function of both the intensity (Rechter
Scale) and its duration. The most dangerScale) and its duration. The most danger
effect occurs when the vibration iseffect occurs when the vibration is
perpendicular to the face of the dam.perpendicular to the face of the dam.

10. • Body Forces:Body Forces:
Body force acts horizontally at the center ofBody force acts horizontally at the center of
gravity and is calculated as:gravity and is calculated as:
WhereWhere αα is the earthquake coefficient and Wis the earthquake coefficient and W
is the weight of the dam. Is taken 0.2is the weight of the dam. Is taken 0.2
for practical reasons.for practical reasons.
WPem α=
α
W1
0.1 W1
W2
0.1 W2

11. • Water Force:Water Force:
Water vibration produces a force on the damWater vibration produces a force on the dam
acting horizontally;acting horizontally;
Where CWhere Cee is another coefficient (0.82) and his another coefficient (0.82) and h
is the height of the wateris the height of the water
2
3
2
hCP eew α=
2/5 h
h Pew

12. • Example:Example:
Calculate the forces on given dam if;Calculate the forces on given dam if;
γγmm = 2.5 t/m= 2.5 t/m33
,, γγww =1 t/m=1 t/m33
, hw = 1.5 m, hw = 1.5 m
6m
24m
30m
10m
33m

13. • 1. Weight of water1. Weight of water
WW11=2.5 * 6 * 40 = 600 t=2.5 * 6 * 40 = 600 t
WW22=2.5 *0.5*18*30=2.5 *0.5*18*30
= 675 t= 675 t
• 2. Water Pressure2. Water Pressure
P = 0.5 * 1.0 * (33)P = 0.5 * 1.0 * (33)22
= 544.5 t= 544.5 t
w1 w2
P

14. • 3. Uplift3. Uplift
U = 0.5 * 1.0 * 33 * 24U = 0.5 * 1.0 * 33 * 24
= 396 t= 396 t
• 4. Wave Pressure4. Wave Pressure
PPww = 2.4 * 1.0 * 1.5= 2.4 * 1.0 * 1.5
= 3.6 t= 3.6 t
U
Pw

15. • 5. Earthquake Forces5. Earthquake Forces
a. Body Forcesa. Body Forces
PPem1em1= 0.1 * 600= 0.1 * 600
= 60 t= 60 t
PPem2em2= 0.1 * 675= 0.1 * 675
= 67.5 t= 67.5 t
b. water Forceb. water Force
PPewew=(2/3)*0.82*0.1*(33)2=(2/3)*0.82*0.1*(33)2
= 59.55 t= 59.55 t
Pem1
Pem2
Pew