Homework Help: Question about tension and deflection (Mechanics of Material)

1. Feb 12, 2010

shinizaki

Hello everyone, I have some difficulties to solve this question in my homework.

1. The problem statement, all variables and given/known data
Picture
http://img714.imageshack.us/img714/7953/picz.png [Broken]

Rigid bar ACE connected to rod AB, CD, EF which have same material and surface area A. Calculate tension caused by force P in three rods.

2. Relevant equations
Equation :
sigma Fy = 0
sigma M =0
comparison between deflection in A, C, and E

3. The attempt at a solution
I try to solve this question but I can't find sufficient equation to solve it. It have 4 equations and I only find 3. Please help me solve this.

Last edited by a moderator: May 4, 2017
2. Feb 12, 2010

Mapes

Have you tried summing the moments around different points?

3. Feb 12, 2010

pongo38

You haven't shown your working, but have you considered the property of the bar that it is rigid? What does that imply for the displacements of A, C and E?

4. Feb 12, 2010

PhanthomJay

these are your 3 relevant 'equations'
there are 3 relevant equations (as you note; the last is concerned with geometric compatability) and 3 unknowns (the tensions in each rod). What do you mean by four ?(the x direction is irrelevant here). Note that the bar is rigid, but that the rods can extend or compress (which should have been more clearly stated in the problem). Hint: This problem is best solved by replacing the force P with an equivalent force-couple system at midpoint.

5. Feb 13, 2010

shinizaki

When I try a few times again, I can solve it at last ! The unknown P I change to one so I have 3 unknowns and 3 equation then revert it back to P. Thanks all^^