Truss Method of Joints: Solving Unequal Member Forces

[gmreit]

Homework Statement

The load is known. Just 2 reactions needed to describe all external forces.

Homework Equations

method of joings

The Attempt at a Solution

I'm working on a pretty simple truss for work and want to check some of the elements for buckling. The strange thing is I am not getting equivalent member forces for each side of the truss. Without any additional diagonal bracing in the middle I thought it will be a pretty straight forward case. Not sure what I am missing because I figured Fmn = Fah and Fbc = Ff but I am not getting that.

 

[PhanthomJay]

Firstly, you don't have a truss, because you are missing the diagonals. As a result, you will have bending and shear stresses in the top and bottom chords, so you cannot use the method of joints which pertains to truss members with axial loads only.
Secondly, if you added those diagonals, you could solve for the member forces, but the truss is not symmetrical the way you have drawn it, so you shouldn't expect mirror image forces.

 

[gmreit]

I do see what you are saying. Frame analysis would probably be a better fit I believe since joint A, B,C, D, E, F, G, AND N are pin joints but H thru M are moment carrying joints.