Dear Elena,

Ahhh...I'm starting doubt w/ my way. I start remembering Newton Law III and Free Body Diagram (FBD) concept that if we sum all F&M act inside one system = 0. FBD for Inside one system, all forces and moments neglect each other. Dear Corne is right???...:( Apologize me.

I mean in order to know F&M at node 240 the correct free body diagram should be (240 at the edge of the system):

++++++400++++++
+++++++o+++++++
+++++++|+++++++
+++++++|+++++++
+++++++|+++++++
+++++++o+++++++
++++++240++++++

not like this (node 240 inside the system):

++++++400++++++
+++++++o+++++++
+++++++|+++++++
+++++++|+++++++
+++++++|+++++++
o--------o--------o
230+++240++++245

Note:
o-----o : element
o : node
+ : paper