Statics question: when do I need to find the support reactions?

[denting]

I didn't use the format because my question is more general. I want to be able to understand the logic so I can apply it where appropriate.

We're finding forces (and whether they're in tension or compression) using the Method of Joints and Method of Sections. I don't understand why sometimes it's necessary to find the supprt reactions, but sometimes it's not. Please help. Thank you!

 

[jeffc0987]

I know in the method of joints there are certain joints that can be ignored called "zero force members" as the name implies. Since the question is so general I'm not sure if this is at all what you are looking for. Theres plenty of reference material on the internet to help you out though I am sure.

 

[PhanthomJay]

It is almost always better to solve for the support reactions first before using the method of joints or sections, because it gives you more known external forces up front and makes the solution much easier. Sooner or later you'll need to find them anyway, better sooner than later.

 

[jhae2.718]

I always solve for reactions first as well.

PhanthomJay, I was looking forward to hearing your take on the question.

 

[rwisz]

As a scientist, it is important to understand the underlying principles and logic behind any method or technique used in a scientific field. In the case of statics, the support reactions are necessary to determine the forces acting on a structure. This is because support reactions are the external forces that hold a structure in equilibrium.

In order to analyze a structure using the Method of Joints or Method of Sections, we need to consider the entire structure as a whole. This means that we need to take into account all the external forces acting on the structure, including the support reactions. Without considering the support reactions, our analysis will not be accurate and may lead to incorrect results.

To determine when it is necessary to find the support reactions, we need to consider the type of analysis being done. If we are analyzing a structure using the Method of Joints, we need to find the support reactions at any joint where the external forces are unknown. This is because the Method of Joints relies on the equilibrium of forces at each joint, and the support reactions are part of those forces.

On the other hand, if we are using the Method of Sections, we only need to find the support reactions at the section being analyzed. This is because the Method of Sections relies on the equilibrium of forces and moments acting on a section, and the support reactions are included in those forces and moments.

In summary, the support reactions are necessary to accurately analyze a structure using the Method of Joints or Method of Sections. They represent the external forces that hold the structure in equilibrium and should be considered in any analysis. Understanding the logic behind when to find the support reactions will help you apply these methods effectively in your future analyses.