# Homework Help: Structural Stability & buckling stress

1. Nov 22, 2014

### CivEngMo93

Q: A structure is made from identical, axially compressible robs connected to a rigid foundation. The rods cannot buckle. In the unloaded configuration the angle between the rods and the horizontal is (alpha); then angle becomes (1-Beta)*alpha when p =/= 0. Find the relationship P(Beta). Introduce a suitable non-dimensional load P and make a plot of P vs (beta) the region of -0.5 < Beta < 2.5.

My attempt:
I thought og using the Total potential energy approach, TPE = SE - Work done.... but i have no idea how to get started on it. There is another method called the equilibrium method that my tutor talked about but i cant make any sense of how to start it..

Any help will be much appreciated.

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2. Nov 22, 2014

### Dr.D

What ever in the world does p =/= 0 mean?

3. Nov 22, 2014

### CivEngMo93

Sorry, its meant to mean when P does not equal 0.

4. Nov 22, 2014

### CivEngMo93

I have got strain energy = 0 so far. Since both foundation pins are fixed and do not mov. Therefore potential energy will be a negative value but am unsure about this... In all the examples and tutorials we had. Potential energy is a positive value.

5. Nov 22, 2014

### Dr.D

If strain energy is zero, the length of the bars has not changed, so the geometry has not changed. I think you are on the wrong track with that.

Your original statement about work and energy sounded promising, so why not pursue that?

What is the strain energy of an axially compressed bar?

6. Nov 22, 2014

### Staff: Mentor

If the pin moves downward a distance δ from its initial location, what is the new length of each rod? You need this to get the strain in the rod.

Chet