| Abstrakt: |
Under ordinary atmospheric conditions air-dried timber quickly reabsorbs moisture and undergoes certain changes in its characteristic properties. In order to determine how much greater would be the response and the consequent change in properties if the timber timber introduced into a saturated atmosphere at a reasonably high temperature or if completely submerged in water, a series of investigations was conducted during the past year at the Massachusetts Institute of Technology on two important structural timbers — Douglas fir and southern hard pine. These tests are described in detail in the paper and the results obtained presented in the form of graphs. While these tests were made on a limited number of small specimens and the results are confessedly comparative and qualitative rather than quantitative, the author is nevertheless of the opinion that an analysis of the data given will justify the following statements: In the air-dry condition with approximately equal moisture contents the compressive strength of hard pine is about 25 per cent greater than that of Douglas fir. When exposed to air saturated with water vapor at 120 deg. fahr., and when immersed in fresh water at 70 deg. fahr., the moisture reabsorption of air-dried fir is greater and more rapid than that of pine. The temperature effect on strength decrease is of more importance on pine than on fir. Pine shows a more rapid decrease in strength with the moisture increase than does fir. (The more rapid reabsorption by fir tends to offset this effect when the time element is used as a basis, so that for a given time of treatment the pine remains the stronger although the strengths tend to approach each other with more extended treatment.) For moisture contents above 11 per cent when due to reabsorption from air saturated at 120 deg. fahr., the fir is stronger in compression than the pine. The same relation appears for moisture contents greater than 20 per cent when due to soaking in fresh water at 70 deg. fahr. |
