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: Question on beams

  1. Apr 16, 2012 #1
    1. The problem statement, all variables and given/known data
    a solid rectangular section beam has a cross section: 0.1m x 0.2m, and length 2m is simply supported at each end. A load of 1100N is applied at the middle of the span.
    a) find the maximum bending stress and specify the location of the bending stress
    b) to reduce weight a hollow rectangular section beam having an outside horizontal dimension of 0.2m and a constant wall thickness of 0.02m is to be designed. determine a suitable vertical dimension so that the maximum bending stress is the same as a)

    2. Relevant equations
    I= (bd^3)/12 for a solid rectangular beam
    I = (BD^3)/12 -(bd^3)/12 for a hollow rectangular beam

    3. The attempt at a solution
    a) think ive done it, needs checking.
    Mmax = 1/4FL
    maximum stress = (Mmax/I)x 1/2 x d
    max stress = (0.25x1100x2)/(0.1x(0.2)^3/12) x0.5 x 0.2
    max stress = 825000

    b)have to use 825000(or if i have it wrong whatever the correct answer for stress is) and
    use I = (BD^3)/12 -(bd^3)/12 for the value of I this time and plug it back into maximum stress = (Mmax/I)x 1/2 x d , only thing is i'm having trouble rearranging everything to get the value of the vertical height, any help please?
  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