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Regarding the question about creep asked in a closed thread

Regarding the question about creep asked in a closed thread

Regarding the question about creep asked in a closed thread

thread173-255112: Basis of the Load Duration Factor for Wood: Cd

From the Wood Handbook - Wood as an Engineering Material Page 5-39 (a free download from http://www.fpl.fs.fed.us/products/publications)

"Unloading a member results in immediate and complete recovery of the original elastic deformation and after time, a recovery of approximately one-half the creep at deformation as well. Fluctuations in temperature and humidity increase the magnitude of the recovered deformation."

Garth Dreger PE
AZ Phoenix area

RE: Regarding the question about creep asked in a closed thread

The first sentence is not true if the moisture content of the wood varies during the loading, going from a wet to a dry state.  That process is how wicker chairs are made, among other things.

However, if the member is rewetted, it can be loaded back into shape and re-dried to attain it's original shape.   

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Regarding the question about creep asked in a closed thread

Actually the above is true and bending of wood is done this way
"Plasticizing Wood
Principles of Plasticizing and Bending
In simple terms, the wood cell wall is a composite made of a rigid cellulose polymer in a matrix of lignin and the hemicelluloses. The lignin polymer in the middle lamella and S2 layer is thermoplastic; that is, it softens upon heating. The glass transition temperature Tg of the lignin in the matrix is approximately 170 °C (338 °F). Above the matrix Tg, it is possible to cause the lignin to undergo thermoplastic flow and, upon cooling, reset in the same or modified configuration. This is the principle behind bending of wood.
The matrix can be thermoplasticized by heat alone, but the Tg of the unmodified matrix is so high that some fiber decomposition can occur if high temperatures are maintained for a lengthy period. The Tg of the matrix can be decreased with the addition of moisture or through the use of plasticizers or softeners."

from the same book noted above but in chapter 19.

Garth Dreger PE
AZ Phoenix area

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