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!

Finding support reactions for shear and moment diagrams

  1. Apr 24, 2014 #1
    Draw the shear and moment diagrams for the beam in the figure. Clearly show all values, including the maximum shear and maximum moment and their positions on the diagrams. Assume the supports at A and C are rollers and D is a pin support. note there is a hinge at point B.

    I am having trouble finding the support reactions.
    My attempt is:
    (Assuming positive Y direction is up)
    Moment about b = 10(60)+10A-2(10)5=0
    A=-50 kN

    Forces in y direction = C+D-50-2(10)-5-18=0
    C+D=93

    Moment about D= C(12)+60(32)-(50)32-(20)(27)-5(16)-18(6)=0
    C=34

    D=93-34=59
     

    Attached Files:

  2. jcsd
  3. Apr 25, 2014 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Your work is generally very good, however, your error is in the calculation of the moment due to the applied couple at A. You are incorrectly multiplying that couple by a moment arm. The moment of a couple about any point is the couple itself.
     
  4. Apr 25, 2014 #3
    So it would be
    Moment about b = 60 +10A-2(10)5=0
    A=4 kN

    Moment about D = C(12)+60-50(32)-20(27)-5(16)-18(6)=0
    C=189kN

    Forces in y direction=C+D+4-(2)10-5-18=0
    D=-150kN
     
  5. Apr 25, 2014 #4

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    yes
    You still used A = -50 instead of A = +4
    make necessary corrections. It is a good idea to look at the FBD of the beam between B and D to check results.

    Welcome to PF!:smile:

    Note: My lightweight monitor made it easy to turn it upside down.:wink:
     
  6. Apr 25, 2014 #5
    Sorry about the image being upside down! I didn't realize that. And thank you for the warm welcome.

    So
    Moment about D= C12-18(6)-5(16)-2(10)27+4(32)+60=0
    C=45

    Forces in y =D+4+45-20-18-5=0
    D=-6

    Note (the new pictures going to be sideways. I can't figure out how to fix it on my iPad.) sorry!
     

    Attached Files:

  7. Apr 26, 2014 #6

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You should show the negative 6 support reaction at D as a downward force of magnitude 6. Otherwise your reactions, shear, and moment diagrams are literally perfect, correctly curved, etc. , this is excellent work.
     
  8. Apr 26, 2014 #7
    Thank you for all the help! Preparing for finals.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Finding support reactions for shear and moment diagrams
Loading...