1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Analysing a 3D truss problem

  1. Oct 31, 2011 #1
    1. The problem statement, all variables and given/known data

    I am trying to analyse a 3D truss problem (attached). The idea is that when you pull with a force F in the direction of the arrows, the pin in the middle will be pressed downwards, decreasing the length of p2. In general the overall structure will be consistent of a series of these in both directions.

    I am having some difficulties getting started with this. As far as I can tell I should be ok to only analyse the section shown in the bottom picture?

    2. Relevant equations
    I wish to get some sort of solution that relates the length L1 and L2 to p1 and p2.

    3. The attempt at a solution
    My first attempt at this is to use simple statics in 3D:

    Point at top of pin:
    Sum(F_y) = 0
    0 = - F_(BE) - F*sin(Beta)*2 (symetry)

    Sum(M_top) = 0
    0 = - F * sin(Beta)*2*p_1 + F*cos(Beta)*A_1-F*cos(Beta)*A_1+F*sin(Beta)*2p_2

    So something clearly goes wrong here since I just end up with p1 = p2?

    Can anyone help me in the right direction?

    Attached Files:

  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted