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Homework Help: Youngs modulus - stress- check please - easyish

  1. May 26, 2010 #1
    1. The problem statement, all variables and given/known data
    A steel beam is used in the road bed of a bridge. The beam is mounted between two concrete supports when the temperature is 23⁰C, with no room for thermal expansion. What compressional stress must the concrete supports apply to each end of the beam, if they are to keep the beam from expanding when the temperature rises to 42⁰C?
    Assume: Co-efficient of linear expansion for steel = 11 x 10-6K-1
    Young’s modulus for steel = 210GN.m-2



    2. Relevant equations
    stress = F/A=Y deltaL/L
    deltaL/L=alpha deltaT


    3. The attempt at a solution
    I got 0.04389N/m^2
    the reason i out this up is that the compressional stress i found seem very small???
     
  2. jcsd
  3. May 26, 2010 #2

    PhanthomJay

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    Are your units of temperature (degrees K or degrees C) consistent?
     
  4. May 26, 2010 #3
    You have an exponent error somewhere. Remember Giga is 10^9. Check you math.
     
  5. May 26, 2010 #4
    Celsius
     
  6. May 26, 2010 #5
    rtw69 there is no giga anything in the question, what do you mean???? what answer did you get??
     
  7. May 26, 2010 #6

    PhanthomJay

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    Oh sorry, the coef of expansion per degrees K is the same as the coef of expansion per degrees C. As RTW69 noted, don't forget the G (Giga) as in Y = (210)(10)^9 N/m^2
     
  8. May 26, 2010 #7
    ohhhhhhhh ok i didnt even see that big G sitting there... thanks is your answer apart from the index the same as mine?
     
  9. May 27, 2010 #8

    PhanthomJay

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    Yes.
     
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