# Finding point loads in shear force diagram

• Sl1ver
In summary: Can you do this for the points A, B, C, and D?Here is the diagramA. The shear force at point A is greater than the shear force at point BB. The shear force at point C is greater than the shear force at point DC. The shear force at point D is the same as the shear force at point A

## Homework Statement

I have a shear force diagram and I am asked to find the magnitudes of the point loads and where are they situated

My question is, what am I looking for to find the point loads in a shear force diagram?

Sl1ver said:

## Homework Statement

I have a shear force diagram and I am asked to find the magnitudes of the point loads and where are they situated

My question is, what am I looking for to find the point loads in a shear force diagram?

## The Attempt at a Solution

I assume you are looking at point loading along the length of a beam. How does the shear force change from one side of the point load to the other? Do you have any examples of shear force diagrams in your textbook involving point loads?

my textbook doesn't really look at it. I've googled but haven't found much.

here is an example

10 m light horizontal beam
it has points ABCD

A at 0m, B at 2m, c at 8m and D at 10m

it goes positive 38N at A then to 34N at B then straight down to negative 16N the line then goes to C to negative 28N and then straight up to positive 30N and then to D and straight down to 0.

Im just not too sure what exactly to look for to determine where a point is.

Do an equilibrium force balance on a tiny section of the beam cut out on either side of one of the point loads. On one side of the cut the shear force is pointing upward, and on the other side of the cut, the shear force is pointing downward. How is the shear force on one side of the cut related to the shear force on the other side of the cut and to the point load?

here is the diagram

Let me guess. The point loads are at points A, B, C, and D. From what you see on the graph, what is the key characteristic of the shear force variation at these locations?

A. It varies continuously
or
B. It undergoes a jump change discontinuity

I would go with B on your question.

Sl1ver said:
I would go with B on your question.

Right. Now how are these jump changes in shear force related to the point loads? Hint: see my first reply.

To be honest I am not too sure.

Imagine that you cut out a small section of the beam on either side of one of the point loads, and replace the internal loading that was present on the two faces of the section with a tensile force, a moment, and a shear force. This tensile force, moment, and shear force are equal to the corresponding quantities within the loaded beam before the cut was made. Now treat the cut-out section as a free body, and perform an equilibrium force balance on the section in the vertical direction. From this equilibrium force balance, you should be able to determine the jump change in the shear force from one side of the section to the other.

## What is a point load in a shear force diagram?

A point load in a shear force diagram is a concentrated force acting at a specific location on a beam. It can be represented by an arrow pointing upwards or downwards depending on the direction of the force.

## How do I identify point loads in a shear force diagram?

To identify point loads in a shear force diagram, look for abrupt changes in the magnitude or direction of the shear force. These changes will indicate the presence of a point load at that location on the beam.

## What is the significance of point loads in a shear force diagram?

Point loads in a shear force diagram can affect the overall structural integrity of a beam. They can cause bending and shearing stresses, which can lead to failure if the beam is not designed to withstand these forces.

## How do I calculate the magnitude of a point load in a shear force diagram?

The magnitude of a point load in a shear force diagram can be calculated using the equation F = V/A, where F is the force, V is the shear force at the location of the point load, and A is the distance from the point load to the nearest support.

## Can a point load be negative in a shear force diagram?

Yes, a point load can be negative in a shear force diagram. A negative point load indicates a downward force acting on the beam, while a positive point load indicates an upward force.