1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Strength of materials- simple truss problem

  1. Aug 27, 2010 #1
    1. The problem statement, all variables and given/known data

    The bars in the truss each have a cross sectional area of 1.2in^2. If the maximum axial stress in any bar is not to exceed 25ksi, determine the maximum magnitude of P of the loads that can be applied to the truss. Determine the elongation of each member.

    E=29,000 ksi


    4930827627_46098ef021.jpg

    2. Relevant equations

    [tex]
    \sigma[/tex] = E* [tex] \epsilon[/tex]

    [tex]\sigma[/tex] = P/A


    [tex]\epsilon[/tex] = [tex]\delta[/tex] / L

    Having trouble with Latex, but the top equation should read:
    sigma=E*epsilon

    the other two equations are stress=force/area and strain=elongation/lenth.

    3. The attempt at a solution

    I got an answer, but I'm not sure if it's correct and if I'm solving this correctly.

    Since I know [tex]\sigma[/tex]=25ksi, and E=29,000 ksi I used [tex]\sigma[/tex]=P/A solving for P, P= [tex]\sigma[/tex]A=(25ksi)(1.2in^2)=30 kip.

    I assumed this to be Pmax.

    Using [tex]\sigma[/tex]=E*epsilon I solved for epsilon. epsilon= [tex]\sigma[/tex]/E=25ksi/29000ksi = 8.62E-4.

    Then used epsilon=delta/L. Solved for elongation, delta. delta=epsilon*L.

    Then I just used plugged in my solved value of epsilon, and then the length of each bar.

    Here's an example for AC: delta=epsilon*L=(8.62E-4)(4ft)(12in/1ft)=0.0414in.


    I'm not sure if this correct since it would mean every bar that is the same length would have the same elongation. Is this correct? Or do I need to solve the system for the forces and then do something? I'm confused. Thank you for the help.
     
  2. jcsd
  3. Aug 27, 2010 #2
    Axial stress is generated by a force perpendicular to the cross section, what is the direction of P in the diagram ?
     
  4. Aug 28, 2010 #3
    Can you determine the force in each member of the truss, as a function of P?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Strength of materials- simple truss problem
Loading...