Getting Started: Solving Joint Problems in Structural Mechanics

[suspenc3]

Homework Statement

See Attachment

Homework Equations

The Attempt at a Solution

Im not really sure how to get started. I understand the method of Joints, and all the solved examples I can follow. I started by analyzing the support reactions, and I am stuck already. There is the force $$P_2$$, and then there are going to be the following forces: $$G_x, G_y, A_x, A_y$$?

Any advice on how to start this problem would be appreciated.

 

[radou]

Im not really sure how to get started. I understand the method of Joints, and all the solved examples I can follow. I started by analyzing the support reactions, and I am stuck already. There is the force $$P_2$$, and then there are going to be the following forces: $$G_x, G_y, A_x, A_y$$?

Any advice on how to start this problem would be appreciated.

Actually, one of the supports should be a roller support, since I assume this is supposed to be a statically determinate system.

Hint: after analyzing the supports, which one is equivalent to a roller support, i.e. which one has only the horizontal component of the reaction?

 

[Astronuc]

There are two pin joints (no moment), and the far right side is free.

 

[suspenc3]

Im going to guess that G can be considered a roller?

 

[suspenc3]

And since the far right side is free, what does this tell me?

 

[Pyrrhus]

Actually, one of the supports should be a roller support, since I assume this is supposed to be a statically determinate system.

Hint: after analyzing the supports, which one is equivalent to a roller support, i.e. which one has only the horizontal component of the reaction?

That condition is not needed in order for the truss to be statically determinate.

Remember in order for a truss to be statically determinate the number of bars (each carries a force) + the number of reactions must be equal to twice the number of joints (2 equations of equilibrium for each joint).

In this case, there are 10 bars, and 4 reactions, and 7 joints. This truss is statically determinate.

I would solve it by using the section method and start by cutting the members BC, FC and EF.

supenc3. are you familiar with zero force members? that's what astronuc is implying. Note that if you use the joint method at D, and sum forces on y, you will get that DC must be a zero force member.

 

[suspenc3]

No, I am not really familiar with Zero Force members, but it is my book so Il try to look over it. Il go and try it again...Thanks

 

[radou]

Remember in order for a truss to be statically determinate the number of bars (each carries a force) + the number of reactions must be equal to twice the number of joints (2 equations of equilibrium for each joint).

I know, I actually went wrong about the roller support fact; if it was a roller support, it would be a mechanism.

Edit: I dislike sketches of this kind, since for some reason, they tend to confuse me.