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: Determine the absolute maximum bending stress of the beam.

  1. Apr 19, 2016 #1
    1. The problem statement, all variables and given/known data
    If w = 74 kN/m , determine the absolute maximum bending stress in the beam in MPa.
    2. Relevant equations
    I'm not too sure how to go about my calculations. Please help! 1.png

    3. The attempt at a solution
    I = [(1/12)*(200*256^3)] - [(1/12)*(192*250^3)] = 29.62*10^6
    F = 74*24*1000?
  2. jcsd
  3. Apr 19, 2016 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I assume that F is the upward force in Ns at each end, but it's 2.4m not 24m.
    Pick a point at distance x <2.4m from one end. What is the moment of all the forces on one side of it about that point?
  4. Apr 19, 2016 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The calculation for I is wrong. This beam has an overall depth of 266 mm, not 256 mm.

    The calculation of the equivalent force at each end of the beam is wrong. w = 74 kN / m and extends over a distance of 2.4 m at the ends. You can't ignore those pesky decimal points.

    You should get in the habit of recording units with the results of each of your calculations. It eliminates confusion.

    The first thing to do is to draw a free body diagram of the beam and find the reactions at each end which keep the beam in equilibrium.

    Once you know all of the loadings on the beam, you can construct the shear force and bending moment diagrams to determine the max.bending stress.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted