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Deformation of wood under load Siopongco, Joaquin Ordonez

Abstract

Creep and recovery tests in compression parallel to the grain were conducted on 2 in. by 2 in. Douglas-fir specimens 4 in. long at four different levels of moisture. Specimens were loaded in stages up to a predetermined load. Instantaneous axial and lateral deformation as well as creep measurements were taken at each stage. Creep was observed over periods ranging from five minutes to twenty-five hours. Similarly, recovery was observed during unloading at successively lower stress levels. There are indications that creep as well as negative creep and negative recovery were mainly due to moisture present in the cell walls. Creep, In general, appeared to be more marked in the green specimens than in the intermediate and air-dry conditions. The only oven-dry specimen showed less creep than the air-dry specimens. Results also show that the values of the coefficient of lateral deformation(formula omitted) (both radial and tangential), during the load rise were entirely different from those during the period of creep, indicating that the corresponding deformations were entirely different. The µ’s for the change In load were always higher than those for the periods of creep. All specimens tested showed a recovery of more than 50% of the longitudinal creep. This indicates that creep in wood is made up of two parts, recoverable and permanent creep.

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