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Properties of Plank wood & bridge question

by Ngineer
Tags: bridge, plank, properties, wood
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Ngineer
#1
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!

Thanks
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jim mcnamara
#2
Oct27-12, 07:12 PM
Sci Advisor
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P: 1,384
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

http://www.fpl.fs.fed.us/products/pu...00&header_id=p

But you need to have a clue as to what wood species you are going to use.
AlephZero
#3
Oct27-12, 08:16 PM
Engineering
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Thanks
P: 7,172
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 ...


Bavid
#4
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 (http://www.amazon.com/Materials-Sele.../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.
Engineer_Phil
#5
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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