# Homework Help: Truss Analysis

1. Nov 1, 2013

### reyna12

Hi there, i hope someone can help me.

I am just unsure how to proceed with this problem.

1. The problem statement, all variables and given/known data

The question and diagram can be found in the attached image. I am looking for assistance on part (ii)

2. Relevant equations

1. Summation of Moment = 0
2. Summation of forces along x - axis = 0 ;
3. Summation of forces along y - axis = 0 ;

3. The attempt at a solution

Design Loads calculated as 142.36kN at Node C and 71.23kN at Node D using EQ (6.10)

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2. Nov 1, 2013

### PhanthomJay

Did you sum moments to find the support reactions at A and E in the horizontal direction? Is there a vertical force at E?

3. Nov 2, 2013

### reyna12

Confused entirely in all honesty. I had attempted to but it's probably just meaningless scribbles.

+veƩM = 0 ... (HA×4)+(142.46×8)+(71.23×4) = 0
HA = -356.28kN

+ve→ƩFχ = 0 ... +(HA)+(HE)=0
HE = +356.28kN

+ve(vertical)ƩFy = 0 ... +(VA)+(VE)=0
+(VA)+(VE) = 213.69
VA = 213.69 - VE

4. Nov 2, 2013

### PhanthomJay

Honesty is the best policy.
No-o .
you mixed up the 4 with 8 and vice versa.
Yes , but VE equals ????? Use method of joints at E to find VE which is ?

5. Nov 7, 2013

### reyna12

Ok i think I've figured it out?

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6. Nov 7, 2013

### PhanthomJay

Yes, that looks good, but you need to convince yourself (if you haven't already) that the force is a compressive force and not a tensile force.

7. Nov 7, 2013

### reyna12

That's what I'm struggling with, are you able to offer a quick explanation?

8. Nov 7, 2013

### PhanthomJay

Well, OK. When you look at a free body diagram of forces acting on a joint, if the member force points toward the joint (that is, pushing toward the joint), it is in compression; if it points away from the joint (that is, pulling away from the joint), it is in tension.

The same applies if you are looking at internal forces at a cut section of a member (method of sections): if the force is pushing toward the member, it is compressive; if it is pulling away from the member, it is tensile.