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Force Resolving Structural Engineering Problem

  1. Nov 9, 2005 #1
    Can someone please help me start this question, I missed some vital notes in class and don't know how to do it. I just need to know the method so I can go on to do it myself Thanks :)

    Last edited: Nov 9, 2005
  2. jcsd
  3. Nov 9, 2005 #2


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    Staff: Mentor

  4. Nov 14, 2005 #3
    Thanks for the help but i'm still a little stuck. I can work out the magnitudes fine but i'm a bit confused as to where the negatives should be and what they actually represent. This is my working so far (the joints are labelled A-K from left to right):

    Fab = Force along member AB

    Consider Joint A:

    Sum of Verticals at A=25+Fab*sin60=0

    Since this is negative it is a compressive force.

    Sum of Horizontals at A=Fab*cos60+Fac=0

    Since this is positive it is a tensile force.

    Consider Joint B (This is where I get confused:

    Sum of Verticals at B=Fab*sin60+Fbc*sin60+Fbd*sin0=0

    Since this is negative it is a compressive force.

    Sum of Horizontals at B= Fab*cos60-Fbc*cos60+Fbd*cos0=0

    Have I got all of the negatives right because I really have no idea how they are determined and also, is it even possible for Fbd to have a force of 0N on this bridge given that there is a force of 50N on the center of the bridge?

    Thanks for any help.
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