DISCUSSION THREAD
Hints:
For Part A - Use the four-step plan:
1. Equilibrium - FBDs of the connectors and writing down the equilibrium equation for each.
2. Load/deflection - Write down the load/deflection equation for each element: e = FL/EA.
3. Compatibility - Starting from the left end, add up the elongations for the three elements. This sum equals the displacement of end H, uH. What is uH in this case?
4. Solve - Count the number of equations and the number of unknowns. If you have sufficient equations, solve. If not, go back to Steps 1-3 to see what you are missing.
For Part B - Use geometry to relate the elongations of the two elastic members. Be careful with the signs in relating elongations to displacements.
Any questions? Ask (and answer) questions here.
what is the "ith" member for part B? And what does it mean by Fi>0 and ei>0?
For each structure in Part B, there are two members: (1) and (2):
* F_1 and F_2 are the loads carried in members (1) and (2), respectively.
* e_1 and e_2 are the elongations of members (1) and (2), respectively.
The statement about which you are asking is simply a statement of the sign convention for these member loads and member elongations; that is, positive values for member loads F_i and member elongations e_i correspond to tension.
For Part B, what is a compatibility equation?
Compatibility equations relate member elongations to displacements of points. This is covered in the lecture and in the examples worked out in lecture.
Are we expected to draw FBDs for part b? Or can we just write the equations directly?
The FBDs will be drawn for Part a) where you solve for the member loads (in Step 1), and from those, the stresses.
Calculating displacements come directly from the compatibility equations. There is no need for FBDs there.