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Properties of Plank wood & bridge question

  1. Oct 27, 2012 #1
    Hello everybody,

    For a group project, we are supposed to propose several designes for a plank bridge over a river.

    I've tried to find this material's (plank wood) strength properties, or a stress-strain diagram to no avail. Do you know where I can find it?

    Also, is it reasonable for a wooden bridge to be 2-3km long? Do we need supports over the river to make it safe and practical?

    Your help is greatly appreciated!

  2. jcsd
  3. Oct 27, 2012 #2

    jim mcnamara

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  4. Oct 27, 2012 #3


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    This is what a bridge just over 2km long might look like ...

    http://inbarton.110mb.com/bridgecurve.jpg [Broken]http://inbarton.110mb.com/bridgeair.jpg [Broken]
    Last edited by a moderator: May 6, 2017
  5. Oct 31, 2012 #4
    First things first. If you have decided your construction will be based on wood, you can find the approximate material properties in Michael Ashby's book on Materials Selection (https://www.amazon.com/Materials-Selection-Mechanical-Design-Fourth/dp/1856176630).

    The properties you are looking for are the following: Flexural strength, buckling strength and tensile strength for a 'wood-like' material. Also, it is literally impossible that you can build a 2-3 km structure out of a single plank of wood that is supported only at the ends - if it somehow escapes bending under its own weight it will still easily be swayed by winds. Maybe I am giving you more complicated advice than you need, so just look up Ashby's book first. It deals with several nice examples regarding how to select a material for specific objectives.
    Last edited by a moderator: May 6, 2017
  6. Nov 2, 2012 #5
    If your plank has a large enough area moment of inertia you could use one plank and not have excessive swaying... but good luck finding a tree that size...
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