Calculating the Moments on the Walls of a Tank filled with Water

[tomtomtom1]

Homework Statement

Calculating Moments of a Tank Wall of Water

Relevant Equations

F = p * g * a * y

p = density of water (1000)

g = gravity (9.81)

a = area (36)

y = distance from the top of the tank to the walls centroid (1.5)

Hello all,

I was hoping someone could help me calculate the moment a tank wall experiences.

I have the following question:-

Tank contains water with dimensions:
4m Wide
12m Long
3m Tall

Determine the moment at the bottom of the long side at its centre.

I have drawn a sketch of the tank and highlighted in dark what I believe is the "bottom of the long side"

To calculate the force acting on the wall (12 x 3) I have done the following:-

F = p * g * a * y
p = density of water (1000)
g = gravity (9.81)
a = area (36)
y = distance from the top of the tank to the walls centroid (1.5)

1000 * 9.81 * 36 * 1.5 = 529740 N of force acting on the wall.

I think that since i have a total force of 529740N acting on the long side of the wall then to calculate the moment at the centre of the long side i would do (12/2) * 529740 = 3178440Nm.

The reason i have done this is because moment is distance (in this case 6m) multiplied by perpendicular force (in this case 529740) i have been told that this is wrong.

I am not really sure where to go from here?

Can anyone help?

Thank you.

 

[BvU]

i would do (12/2) * 529740

Assign symbols to variables and work with symbols instead of numbers. You know why, I hope ?

12/2 is no good at all. Why ?

Make a cross section at the center of the long wall and draw the force on the wall at the proper distanc from the bottom.

1000 * 9.81 * 36 * 1.5 = 529740 N of force acting on the wall

Didn't we just do an exercise on how to calculate such a force ?

 

[tomtomtom1]

Assign symbols to variables and work with symbols instead of numbers. You know why, I hope ?

12/2 is no good at all. Why ?

Make a cross section at the center of the long wall and draw the force on the wall at the proper distanc from the bottom.

Didn't we just do an exercise on how to calculate such a force ?

BvU

I got it thanks.

I was looking at the tank from the wrong perspective.

Calculated by force as 529.2kN
Moment worked out to be 529.2kNm because when i projected centriod of the force distribution i got 1/3 of 3m which is 1m and moment is distance * force which got me 529.2kNm.

Thank you for your patience.