Help with Structural Engineering Problem: Summation of Forces/Moments

[reyna12]

Hi there, i hope someone can help me.

I am just unsure how to proceed with this problem.

Homework Statement

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

Homework Equations

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

The Attempt at a Solution

Design Loads calculated as 142.36kN at Node C and 71.23kN at Node D using EQ (6.10)Thanks for your assistance.

 

[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?

 

[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

 

[PhanthomJay]

Confused entirely in all honesty.

Honesty is the best policy.

I had attempted to but it's probably just meaningless scribbles.

No-o .

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

you mixed up the 4 with 8 and vice versa.

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

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

Yes , but VE equals ? Use method of joints at E to find VE which is ?

 

[reyna12]

Ok i think I've figured it out?

 

[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.

 

[reyna12]

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.

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

 

[PhanthomJay]

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

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.