Engineering - For beginners Part 7

Started by RAB, January 21, 2005, 12:10:30 AM

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Engineering - For beginners Part 7
    The role of Fiber strength in wood and other materials.

The strength of any material is based on the fibers that compose that material
Higher strength materials have a higher resistance to permanent deformation and failure.
This resistance is commonly called shear (or resistance to shear).
Also easy to remember as a strong material-
Not to be confused with a material that is stiff (deflects very little under load) although a material can have both higher value properties.

Fiber Strength numbers for common building materials.
Eastern Softwood #3  600
Doug Fir #2              1200
Composite wood       2400
Steel                        36000
Titanium                 72000

Safety factors discussed in Parts 1-5 are based on Fiber Strength numbers.
Notice a doubling of shear numbers for different types of wood.
If you were to see a glue laminated beam in a house you can easily surmise that it is needed for a higher strength number. If it is a beam of great depth - it is sized for deflection.

All wood members have fiber strength values that reflect its size, grade, and species.

For the majority of beam applications, deflection will be the controlling factor rather than Fiber strength.

Interested readers – this is a multipart series.
Engineers please excuse the simplification that this forum dictates.

Ryan B