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Properties of Plank wood & bridge question

by Ngineer
Tags: bridge, plank, properties, wood
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Oct27-12, 06:31 PM
P: 19
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!

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jim mcnamara
Oct27-12, 07:12 PM
Sci Advisor
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There is no such thing as "plank wood" - there are white oak planks, red oak planks, white pine planks.... and so on.

Plus, what you've given us is vague.

Start with the Forest Products Laboratory website - Wood as an Engineering Material

But you need to have a clue as to what wood species you are going to use.
Oct27-12, 08:16 PM
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Quote Quote by Ngineer View Post
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?

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

Oct31-12, 01:36 AM
P: 32
Properties of Plank wood & bridge question

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 (

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.
Nov2-12, 01:22 PM
P: 27
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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