# Shear Force and Moment Diagrams

• TyErd
In summary, the conversation discusses a confusing cantilever problem with negative point loads and distributed loads. The problem also includes a moment/torque, causing confusion in drawing the shear force and bending moment diagrams. The person asking the question attempts to redraw the diagram and change the direction of the loads to make them positive, but is unsure if this is allowed with the distributed load. Another person points out errors in the original problem and suggests providing a scan of the original. The conversation ends with a discussion about the correct shear and moment diagrams for the revised beam.
TyErd

## Homework Statement

This cantilever confuses me so much. The negative point loads and negative distributed load. And is the other one that's -40kN/m moment/torque or something. My question is how do I do the shear force and bending moment diagrams of this. Am i suppose to redraw the diagram and make everything positive by changing the direction? can i even do that especially with the distributed load?

I don't really mind much for the numbers or anything its just the shape of the diagrams.
I've attached the diagram of the cantilever beam.

## Homework Equations

M=Fd where m=moment, f=force and d=perpendicular distance.

## The Attempt at a Solution

i have attempted and attached it and so can anyone tell me if this looks right?

#### Attachments

• scan0003.jpg
10.5 KB · Views: 449
Last edited:
You are confused because your problem diagram makes little sense. The applied torque should have units of kN-m, not kN/m; there is a difference. You also show an applied point load and an applied distributed load, both with negative magnitudes, yet each is drawn acting in opposite directions.

If you can provide a scan of the original problem, that would go a long way in resolving these contradictions.

Yeah i realize the difference between kn-m and kn/m,, silly mistake by me but about the distributed load and point load, that's how the question is given. that is the original problem. negative values. i know its confusing but this is what was given to us. i can just simply switch the directions and make the values a positive right? even the distributed load? can i switch the direction of the torque and make it a positive?

is the shape of the bmd and sfd look right?

Without getting into the problems with the applied loads, no, your shear and moment diagrams are not correct. At the free end of the cantilever (the left end), there are no applied loads. Therefore, the shear and bending moment at this end must be zero. A couple which is applied to the beam produces a jump discontinuity in the bending moment curve just like an applied point load force produces a jump discontinuity in the shear curve.

i've redrawn the diagram and attached it, is this diagram equivalent to the original one?

thats the diagram i used to draw the shear and moment diagrams. are both diagrams incorrect or just the moment?

#### Attachments

• scan0005.jpg
7.6 KB · Views: 427
im pretty sure the shear diagram is right, isn't it??

I don't see any calculations to determine the reactions at the wall. I also don't see any shear or moment diagrams for the revised beam.

## 1. What are Shear Force and Moment Diagrams?

Shear Force and Moment Diagrams are graphical representations of the internal forces and moments experienced by a structural element as a result of external loads.

## 2. Why are Shear Force and Moment Diagrams important?

Shear Force and Moment Diagrams are important because they help engineers and designers understand the structural behavior of a component and ensure that it can withstand the expected loads.

## 3. How are Shear Force and Moment Diagrams constructed?

To construct a Shear Force Diagram, the external loads acting on the component are plotted along the length of the element. The diagram shows the change in shear force at any point along the length of the component. A Moment Diagram is then constructed by integrating the shear force diagram, which shows the change in moment at any point along the length of the component.

## 4. What information can be obtained from a Shear Force and Moment Diagram?

A Shear Force and Moment Diagram can provide information on the magnitude, location, and direction of the internal forces and moments acting on a structural element. This information is crucial for designing and analyzing structural components.

## 5. Are there any limitations to using Shear Force and Moment Diagrams?

While Shear Force and Moment Diagrams are useful tools for understanding the behavior of structural components, they have some limitations. They only consider the effects of external loads and do not take into account other factors such as material properties, temperature, and dynamic loads. Therefore, they should be used in conjunction with other analysis methods for a comprehensive understanding of the structural behavior.

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