# Determine the forces using virtual work(unit force method)

• daphnelee-mh
MaIn summary, the conversation is about determining designated forces using the principle of virtual work, specifically in regards to a multispan beam. The speaker is unsure about how to analyze a subsidiary portion of the beam using virtual work and mentions calculating Yc and Ma. They also mention that they know how to solve the problem without using virtual work, but are struggling with this approach. The other speaker suggests that the method used is not important unless it is a homework problem, which it is in this case.
daphnelee-mh
Thread moved from the technical forums, so no Homework Template is shown
Summary:: Require to determine the designated forces using principle of virtual work ( unit force method )

I have no idea how to determine the multispan beam using virtual work, if I start to analyse the subsidiary portion BC member, the Yc can be calculated and following by the Ma... it seems don’t involve the unit force method

I use the Principle of Virtual Work quite often, but I have to say that I do not see a simple way to employ it here. Is this a homework problem? If not, who cares what method is used?

Yes, this is a homework problem, I know how to solve it if don't use virtual work method, but now I only can find the Yc

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## What is the unit force method?

The unit force method is a technique used in virtual work analysis to determine the forces acting on a structure. It involves applying unit forces in different directions and calculating the corresponding virtual work done by each force. This method is useful for solving complex structural problems with multiple forces and constraints.

## How do you use the unit force method?

To use the unit force method, you first need to identify all the forces acting on the structure and their respective directions. Then, you apply unit forces in each direction and calculate the virtual work done by each force. Finally, you sum up all the virtual work values to determine the overall forces acting on the structure.

## What are the advantages of using the unit force method?

The unit force method has several advantages, including its ability to handle complex structures with multiple forces and constraints. It also provides a systematic and organized approach to determine the forces, making it easier to understand and analyze the structural behavior. Additionally, this method can be easily applied to both 2D and 3D structures.

## What are the limitations of the unit force method?

One limitation of the unit force method is that it assumes the structure is in static equilibrium, meaning that all forces are balanced. This may not always be the case in real-world scenarios where dynamic loads or external factors may affect the structure. Additionally, this method may become time-consuming for large and complex structures.

## How is the unit force method different from other methods of determining forces?

The unit force method is different from other methods, such as the method of joints or method of sections, which rely on equilibrium equations to determine forces. Instead, the unit force method uses virtual work principles to calculate forces, making it more suitable for solving problems with complex geometries or non-uniform loading conditions.

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