Forces Acting on Dams

1
Forces Acting on Dams

• To design a dam, various forces must be
  considered to insure the safety of the dam. The
  most important forces are
• Weight of dam
• Water Pressure
• Uplift
• Wave pressure
• Earthquake forces

2

• Weight of Dam
• The weight of the dam is calculated as follows
• Where ?m is the specific weight of the dams
  material.

3

• Water Pressure
• Water pressure acts perpendicular to the surface
  of the dam and is calculated per unit width as
  follows
• Where ?w is the specific weight of water and h is
  the height of water.

4

• Uplift
• Dams are subjected to uplift force under its
  base. Uplift acts upward.
• Where B is the width of the base of the dam.

5

• Wave Pressure
• The upper part of the dam (above the water level)
  is subjected to the impact of waves. The maximum
  wave pressure per unit width is
• Where hw is the wave height.

6
Earthquake Forces

• Dams are subjected to vibration during
  earthquakes. Vibration affects both the body of
  the dam and the water in the reservoir behind the
  dam. Vibration forces are function of both the
  intensity (Rechter Scale) and its duration. The
  most danger effect occurs when the vibration is
  perpendicular to the face of the dam.

7

• Body Forces
• Body force acts horizontally at the center of
  gravity and is calculated as
• Where a is the earthquake coefficient and W is
  the weight of the dam. Is taken 0.2 for
  practical reasons.

8

• Water Force
• Water vibration produces a force on the dam
  acting horizontally
• Where Ce is another coefficient (0.82) and h is
  the height of the water

9

• Example
• Calculate the forces on given dam if
• ?m 2.5 t/m3, ?w 1 t/m3, hw 1.5 m

6 m
10 m
33 m
30 m
24 m
10

• 1. Weight of water
• W12.5 6 40 600 t
• W22.5 0.51830
• 675 t
• 2. Water Pressure
• P 0.5 1.0 (33)2
• 544.5 t

w1
w2
P
11

• 3. Uplift
• U 0.5 1.0 33 24
• 396 t
• 4. Wave Pressure
• Pw 2.4 1.0 1.5
• 3.6 t

U
Pw
12

• 5. Earthquake Forces
• a. Body Forces
• Pem1 0.1 600
• 60 t
• Pem2 0.1 675
• 67.5 t
• b. water Force
• Pew(2/3)0.820.1(33)2
• 59.55 t

Pem1
Pew
Pem2