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Finding the allowable uniform load

  1. Dec 14, 2009 #1
    1. Determine the allowable uniform load w if the allowable bending stress is 24ksi and
    P=15w
    Given: I=12,800in^4; c=16.965in



    2. I know that Mmax=[tex]\sigma[/tex]max/c(I); And Mmax=wL[tex]^{2}[/tex]/8



    3. I solved for Mmax=18,107.869 k in; but I dont understand how to solve for w with the two P forces also. If somone could help me with this part I would greatly appreciate it. Thanks
     

    Attached Files:

  2. jcsd
  3. Dec 14, 2009 #2
    some of the moment capacity is used up by the moment of 3P in the central portion of the beam, thus leaving less available for the uniform load. I suggest you first draw the M diagram for the whole beam.
     
  4. Dec 14, 2009 #3
    Thats supposed to be a 3ft from P to the edge, sorry my drawing skills are not great. I already did the M diagram that is where i came up the max of 575. I just dont know how to solve for the w.
     
  5. Dec 15, 2009 #4
    Maybe you are missing the point that p=15w. Therefore M isn't just wL2/8 but also 36x15w=540w k.in at the centre
     
  6. Dec 15, 2009 #5
    O ok, so M would be equal to wL2/8+540w?
     
  7. Dec 15, 2009 #6
    Yes, but be careful to use consistent units throughout. Like kip inches, or whatever.
     
  8. Dec 15, 2009 #7
    ok thanks for the help
     
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