DISCUSSION THREAD
Hints:
Note that this truss is indeterminate; that is, one cannot determine the member loads through equilibrium alone. In solving, use the four-step plan:
1. Equilibrium - FBD of joint D and writing down the equilibrium equations.
2. Load/deflection - Write down the load/deflection equation for each of the three elements: e = FL/EA.
3. Compatibility - Use the truss compatibility equations relating the u-v components of the displacement of joint D to the elongations of the three members.
4. Solve - Count the number of equations and the number of unknowns. If you have sufficient equations, solve for the axial forces in the members, and from those calculate the stresses. If not, go back to Steps 1-3 to see what you are missing.
Any questions? Ask (and answer) questions here.
I am confused on if theta_1 is 0 degrees or 180 degrees. The x-axis in this problem is oriented differently than the examples we did in class. So, when I take the angle from the x-axis it looks like it is 180 but I am not sure.
Theta_1 is the angle of member 1 measured from the positive x-axis at the BASE point of the member. The x-axis here is positive to the right - how is that different from what we did in class?
By the above definition, it appears that theta_1 = 180°.