Sayfadaki görseller
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All the results were now tabulated and reported to the students on mimeographed sheets in the form shown in the table. These results were then plotted by the students with respect to position of the test specimens in the plank, to exhibit more clearly the variations due to difference in the structure of the wood formed at different periods of the tree's growth (Fig. 15). On the whole these results are consistent, though but a

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single specimen represents each actual condition, and illustrate quite forcibly some of the variables in the strength of timber. There is another variable, however, which must be recognized before results like these can be used intelligently in designing, and that is the “time effect.” The strength of timber for permanent loads is only about fifty to sixty per cent. of these values; or, in other words, the ultimate strength of timber for a permanent load is the same as the elastic

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B19 Dry

B22 Normal

825 Wer

FIG. 12.

Hundua

020 Dry

823 Normel

B26 War

Fig. 13.

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room work should be to arouse the student, to make him spe farts and relations clearly, to make him think. To thi's end also some simple problems in designing may be introduced from time to time, illustrating the practical use to be made of these test results. For instance, following the timber tests, the design of a low railroad trestle proves both interesting and instructive, requir

RESULTS OF TESTS OF WHITE PINE-SERIES B-PROPERTIES OF

MATERIALS, 1904.

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B2

B4

I B11

Modulus

of Elasticity

B1
B3

B5

B6
Dry 885,000 1,050,000 1,055,000 1,025,000 1,010,000 870,000 982,500 1.27
B7 BS

B9
B10

B12
Norm. 830,000 965,000 1,000,000 1,040,000 950,000 820,000 '934,200 1.21
B13
B14
B15
B16
B17

B18
Wet 626,000 895,000 840,000

890,000! 700,000 670,000 770,200 1

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Across
Grain
Tensile
Strength

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