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Truss Analysis

  1. Nov 1, 2013 #1
    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)


    Thanks for your assistance.
     

    Attached Files:

  2. jcsd
  3. Nov 1, 2013 #2

    PhanthomJay

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    Did you sum moments to find the support reactions at A and E in the horizontal direction? Is there a vertical force at E?
     
  4. Nov 2, 2013 #3
    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
     
  5. Nov 2, 2013 #4

    PhanthomJay

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    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 ?
     
  6. Nov 7, 2013 #5
    Ok i think I've figured it out?
     

    Attached Files:

  7. Nov 7, 2013 #6

    PhanthomJay

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    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.
     
  8. Nov 7, 2013 #7
    That's what I'm struggling with, are you able to offer a quick explanation?
     
  9. Nov 7, 2013 #8

    PhanthomJay

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    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.
     
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