Solve by method of Sections/Joints

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In summary, the person is having trouble solving a truss using both method of sections and joints. They are asking for help and have found some results, but are unsure if they are correct. They are advised to check their results using equations and to use the method of joints as a special case of the method of sections. The person is reminded to use the laws of equilibrium and to double check their work before the exam.
  • #1
seamus258
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Homework Statement



I am having problems trying to solve this truss by both method of sections and joints and require some help which will be much apprecited as i have an exam tomorrow. Thanks in advance.

load at node c is 60kN and 138kN at node d

This is what i have found but not sure if i am right
At node A i have a horizontal reaction <-- 276kN and vertical upward reaction of 207kN.
At node E i have a horizontal reaction --> 276kN.
 

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  • #2
If your reactions are correct, you can always find out by checking equilibrium using equations as yet not used; for example, taking moments about D should = zero. In this case, I think you may have slipped. Does 207 balance 60 + 138? Try again, or at least check it. Maybe the 60 should be 69? Actually the method of joints is a special case of the method of sections. You cut the structure and replace the cuts with forces that are either known or unknown. Then you make equilibrium statements about each of the objects thus isolated. The diagram you offered is also an example of such an isolated object, and you used the laws of equilibrium to find the reaction components. In this type of question you can check everything with independent equations, and know if you have it right before you leave the examination. That is the best advice I can offer for tomorrow's exam. Best wishes.
 

1. How do I determine the forces in a truss using the method of sections?

The method of sections involves isolating a section of the truss and analyzing the forces acting on that section. The forces can be determined by using the equations of equilibrium and solving for the unknown forces. It is important to choose a section that has a maximum of three unknown forces in order to solve the equations.

2. Can the method of sections be used for both simple and complex trusses?

Yes, the method of sections can be used for both simple and complex trusses. However, it is generally easier to use for simple trusses with fewer members and supports.

3. What are the advantages and disadvantages of using the method of sections?

The advantages of using the method of sections include its simplicity and efficiency in determining the forces in a truss. It also allows for the calculation of forces in specific sections without having to analyze the entire truss. The main disadvantage is that it can only be used for static equilibrium problems and is not suitable for analyzing dynamic or moving loads.

4. How do I choose the appropriate section to analyze in a truss?

When choosing a section to analyze, it is important to consider the forces acting on that section and ensure that it has a maximum of three unknown forces. It is also helpful to choose a section where the forces are parallel to the axis of the truss members, as this simplifies the equations and calculations.

5. Are there any tips for using the method of sections effectively?

One tip for using the method of sections effectively is to label all the known and unknown forces on the truss diagram before isolating the section. This helps to keep track of the forces and ensures that all the necessary equations are set up correctly. It is also helpful to draw the free body diagram of the isolated section to visualize the forces acting on it.

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