How to Calculate Upward Force on Each Anchorage?

[ZeroFive]

Homework Statement

A steel pipeline carrying gas has an internal diameter of 120 cm and an external diameter of 125 cm. It is laid across the bed of a river, completely immersed in water and is anchored at intervals of 3 m along its length.

1. Calculate the buoyancy force per meter run.
2. Upward force on each anchorage.

Density of steel = 7900 kg/m³.

2. Equations used

Buoyancy Force = Weight of the displaced fluid volume

The Attempt at a Solution

I calculated that the buoyancy per unit length is (approximately), 1.204 x 10⁴ N/m
But I don't see a way to find the answer to the second question. Can someone lead me in the right direction or show me how it's done?

 

[TSny]

Welcome to PF!

I calculated that the buoyancy per unit length is (approximately), 1.204 x 10⁴ N/m

OK

But I don't see a way to find the answer to the second question. Can someone lead me in the right direction or show me how it's done?

My hint for this part is to think about whether the weight of the pipe is important in answering the second question.

 

[ZeroFive]

My hint for this part is to think about whether the weight of the pipe is important in answering the second question.

By finding the weight of a unit length and subtracting that from the answer of part 1 gives the additional downward force per unit length the anchor need to provide for the pipe to be in equilibrium. But don't we need the length of the pipe to determine the number of anchors and the total downward force required?

 

[TSny]

By finding the weight of a unit length and subtracting that from the answer of part 1 gives the additional downward force per unit length the anchor need to provide for the pipe to be in equilibrium.

OK

But don't we need the length of the pipe to determine the number of anchors and the total downward force required?

The pipe is anchored every 3 m. Draw a picture and think about the effective length of the pipe that each anchor must hold down.