Dismembering Frames: Discover Reactions and Draw them

[salman213]

http://img524.imageshack.us/img524/1233/fic06p099kb5.png


Ok Here is a frame

I have a FINAL comming up and was just wondering

IF i had to DISMEMBER frame AG

what would be the reactions...

like I know there will be Ax and Ay due to a PIN JOINT and Gx and Gy BUT ! -- Since there is a member ABC will there be any reactions due to it. And if so how would I draw them?

like


there is

AX AY, now is there A2X and A2Y because of member abc?

 

[PhanthomJay]

http://img524.imageshack.us/img524/1233/fic06p099kb5.png


Ok Here is a frame

I have a FINAL comming up and was just wondering

IF i had to DISMEMBER frame AG

what would be the reactions...

like I know there will be Ax and Ay due to a PIN JOINT and Gx and Gy BUT ! -- Since there is a member ABC will there be any reactions due to it. And if so how would I draw them?

like


there is

AX AY, now is there A2X and A2Y because of member abc?

You should always first determine reactions by looking at forces and moments external to the system, before you start dismembering the frame and looking at internal forces. So first calculate the reactions looking at the system as a whole. Then take apart the member AG and the forces at joint G will pop up at you.

 

[salman213]

Hi thanks for replying,..Ys i know i always look at it as a whole and solve for any reactions possible BUT I am just wondering what the reactions WOULD be... IF i dismember AG

 

[PhanthomJay]

Hi thanks for replying,..Ys i know i always look at it as a whole and solve for any reactions possible BUT I am just wondering what the reactions WOULD be... IF i dismember AG

I'm sorry, I didn't give this problem enough thought. I incorrectly was assuming that after calculating the external reactions, it would be a simple matter to dismember the frame and calculate member forces on the the assumption that they would take axial loads only as in a truss. However, this is not the case, since there are bending moments and shears involved, such that, for example, there exists vertical shears and moments in the top horizontal member ABC, and it is not clear how the reaction forces at A would distribute at that joint. Right now, I'm going back to the drawing board, but my mind is blank. I hope someone else can shed some light.

 

[Pyrrhus]

Hey salman what's the problem statement? are you supposed to find only the reactions? the forces acting on each member? or the internal loading (shear, axial and bending diagrams) of each member?