Method of Joints, Virtual Load

In summary, the conversation is about a student struggling with a unit load method question at university, specifically with calculating the force on the members. The question asks for forces in terms of load P, but the presence of 4 pin joints and 4 bars makes it difficult to solve. Other students have removed members to make the structure determinate, but the method is not taught in the course and the student does not want to assume it is correct. One person suggests that the structure is statically indeterminate and that removing members can make it easier to solve. The student plans to research this concept and may reach out for related questions in the future.
  • #1
EngineeringDave
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Hi I was hoping someone could clear something up for me, I've been set an virtual load (unit load method) question at University, that part of the question I can do however its the calculating the force on the members part that I am struggling with.

The question asks for all the forces in the members as a function of load P using the unit load method, however as there are 4 pin joints (Ay and Bx can cancel) and 4 bars using any equilibrium, joints or moment calcs I can't get each member only in terms of P.

Other students have removed members to do this however as this "method" they are using isn't in the course note and I can't find it online I don't want to just assume they are right.

I've drawn the system In the file uploaded.

Thanks In Advance

Dave
 

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  • #2
I think your frame is statically indeterminate. Your classmates are removing members in order to make the resulting determinate. It's much easier to apply the various analysis techniques to a determinate structure, in order to determine the additional equation or equations necessary to allow solution.
 
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  • #3
Okay thanks, I will research this today as I am unfamiliar with the concept.

Thanks Steamking

P.S can I message you with a related quire if I have one?
 

1. What is the Method of Joints?

The Method of Joints is a structural analysis technique used to determine the internal forces in truss structures. It involves analyzing the equilibrium of individual joints in the structure to determine the forces acting on each member.

2. How does the Method of Joints work?

The Method of Joints works by breaking down a complex truss structure into smaller, simpler sections. Each joint in the truss is analyzed separately by applying the equations of equilibrium (sum of forces in the x and y direction equals zero) to determine the forces acting on each member connected to the joint.

3. What is the purpose of Virtual Load in the Method of Joints?

Virtual Load is a technique used in the Method of Joints to help determine the forces in the members of a truss. It involves adding a hypothetical, imaginary load to the structure and using the resulting reactions to solve for the forces in the members.

4. When should Virtual Load be used in the Method of Joints?

Virtual Load should be used in the Method of Joints when there are more unknown forces than equations of equilibrium available. This is often the case in complex truss structures where multiple joints are connected together.

5. What are the limitations of the Method of Joints?

The Method of Joints is limited to analyzing structures that are in static equilibrium and consist of pin-jointed members. It also assumes that the members of the truss are only subjected to axial forces and neglects the effects of bending and shear. Additionally, the Method of Joints may become tedious and time-consuming for larger and more complex truss structures.

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