# Homework Help: Truss Issues

1. Nov 5, 2013

### twj2944

In the attached problem, I don't understand why members CD and DE are equal to 0. I was under the impression that the combined vertical components of BC and CD should equal 6+downward components of BC and EF, as to counteract the force straight down, but this is not the case.

My questions:

Why are the forces in members CD and DE equal to zero?

If they are equal to 0, what stops the downward force from moving the structure?

Thank you

Note: G and Ay are 6 and 6, not 8 and 6 as shown. I used the right values for my calculations, but for some reason wrote 8 down

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Last edited: Nov 5, 2013
2. Nov 5, 2013

### SteamKing

Staff Emeritus
It's not clear from your post: Who is saying that members CD and DE are equal to 0? Are you talking about the forces in these members?

3. Nov 5, 2013

### twj2944

Sorry yes - that's what I meant.

4. Nov 6, 2013

### SteamKing

Staff Emeritus
You still haven't answered the main question: who is saying that the forces in members CD and DE are equal to 0?

5. Nov 6, 2013

### twj2944

The answers in the back of the textbook

6. Nov 6, 2013

### pongo38

IF THE STRUCTURE AND LOADING ARE BOTH SYMMETRICAL THEN THE EQUILIBRIUM OF JOINT d REQUIRES SYMMETRY OF FORCES IN cd AND de. tHAT IS THE CLUE....

7. Nov 6, 2013

### SteamKing

Staff Emeritus
Hey, you don't have to shout.