Internal Forces Diagram: how to do this one?

In summary, the conversation discusses analyzing problems involving internal forces in structures, specifically focusing on Figures 1 and 2. The speaker is confused by the approach their professor took in drawing internal force diagrams for Figure 2, which only included forces in sections AB and BC but not in the imaginary cut at region BD. The recommended method is to first find reactions, then determine internal forces and moments at all joints, and finally draw shear and moment diagrams to determine internal forces and moments in between the joints. The speaker also raises the question of whether separate diagrams need to be drawn for different directions of joints, to which the response is affirmative.
  • #1
ramzerimar
178
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I'm wondering how should I do analysis on those problems below:
Figure 1:
structure1.jpg

Figure 2:
structure2.jpg

I mean, my professor, while doing an example very similar to Figure 2, he didn't do an imaginary cut in the region BD to find internal forces there, and the internal forces diagram that he drew only contained internal forces in sections AB and BC. I'm confused by it. When drawing internal forces diagrams, how should I handle those kinds of problems?
 
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  • #2
After finding reactions, you should determine the internal forces and moments in all members at the joints. Then you can draw shear and moment diagrams to determine the internal forces and moments in between the joints.
 
  • #3
PhanthomJay said:
After finding reactions, you should determine the internal forces and moments in all members at the joints. Then you can draw shear and moment diagrams to determine the internal forces and moments in between the joints.
Okay, so let's consider figure 2. When I draw shear and moment diagrams, I plot internal forces in function of x - where x is the distance related to the origin, let's say, point A. But the structure has joints in other directions - y direction, for instance. So, in this case, I have to draw six diagrams? Three for normal, shear and moment internal forces in the x structure, and another 3 for the joint in the y direction?
I'm confused.
 
  • #4
Yes , if asked to do so, you'll need them for ABC and BD. Even more in figure 1.
 

FAQ: Internal Forces Diagram: how to do this one?

What is an internal forces diagram?

An internal forces diagram is a graphical representation of the internal forces acting on a structure, such as a beam or truss. It shows the magnitude and direction of the internal forces, including tension, compression, and shear forces.

Why is it important to know how to create an internal forces diagram?

An internal forces diagram is crucial for understanding the behavior and stability of a structure. It can help identify potential weak points or areas of stress, and guide the design and construction of a safe and efficient structure.

How do you create an internal forces diagram?

To create an internal forces diagram, you first need to identify all the external forces acting on the structure, including any applied loads or reactions. Then, you can use equations of equilibrium to determine the internal forces at various points along the structure. Finally, these forces can be plotted on a diagram using appropriate scales and conventions.

What are some common mistakes to avoid when creating an internal forces diagram?

One common mistake is to neglect the effects of distributed loads or to incorrectly apply the equations of equilibrium. It is also important to ensure that the internal forces are correctly labeled and plotted in the correct direction and magnitude.

Are there any software tools available for creating internal forces diagrams?

Yes, there are various structural analysis and design software programs that can generate internal forces diagrams for different types of structures. However, it is still important to have a basic understanding of the principles and equations involved in creating these diagrams.

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