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'TABLE IV. Experiments on Pieces of Timler 7.462 inches square, supposing the absolute
Strength 57.85. 220:32 2.931 ?
28,2427 8.528 134
28,243 52.92 26,927 217.62 2.664
(28,026 245.16 3.286
27,599 9:594 153
24,260 5174 23,656 249.00 3.109
s 18,144 12.792 204
| 16,794 325.08 3:553
17,633 50:49 17,318 379.08 4:441
14,688 14.924 24
13,878 379.08 3.997
14,472 | 19:21 14,470 438.48 5.152
s 11,988 17.056 27
12,098 47.98 12,343 435.24 5:596
| 11,772 491.32 5.863
s 10,106 19:188 309
56.69 45:49 491.32
10,424 46.76 10,693 6.218
110,152 545.40 8.350
Š 8,914 21•320 343
9,208 45:51 9,207 540.00 9.060
(20,944 } 21,169 51-68 21,246
TABLE V. Experiments on Picccs of Timber 8.528 inches square, supposing the absolute
30,148 49*68 30,363
129,916 428.76 3•198 12.792 18
56:35 49.87 | 427.14 3.109
25,540 | 48.60 24,883
24,840 497.88 4.0861
s 21,6541 14.924 21
56.78 49.23 | 495.72 3.375
21,605 | 47.52 20,854
21,060 570-24 5.107
s 18,1441 17.056 24
55:42 46.78 | 565.92 6:129
17,968 : 46-4 17,833 | 641.52 4.797 19.188
52:42 42.70 639.64 4.352
14,577 45:36 115,482 1717:12 7.995
$ 11,717 21.320 30
54.10 43.30 1712.80 | 6:396
13,303 44.28 13,593 | 13,176 ]
1614. The five preceding tables give a view of the results of experiments by Buffon upon beams 4.264,5.330, 6.396, 7:462, and 8·528 inches square, of different lengths, as compared with those found by the modified rule above given (1660.).
1615. The first column shows the length of the pieces in English feet. The second, the proportion of their depth to their length. The third, the weight of each piece in pounds aroirdupois. The fourth, the curvature before breaking. The fifth, the absolute or primitive strengtlı, that is, independent of the length. The sixth, that strength reduced in the ratio of the proportion of the depth to the length of the pieces given in the
second column. The seventh column gives the weight borne before breaking, independent of their own weight. The eighth, the mean effort with which the pieces broke, including half their weight, the other half acting on the points of support. The ninth shows the reduced strength of the pieces in respect of the proportions of the depth to the length, supposing the primitive strength equal for all the pieces in the same table. The tenth column gives the result of the calculation according to the rule above given.
1616. In order to give an idea of the method of representing the strength of wood of the same scantling, but of different lengths, by the ordinates of a curve, we annex fig. 613. to explain by it the result of the experiments of Buffon, given in the second table. The ordinates of the polygon N, 0, P, Q, &c. represent the results of the experiments made upon beams 5.330 in. square, of different lengths, whose primitive strength varied in each piece.
1617. The ordinates of the regular curve, m, l, i, h, g, f, e, d, c, b, Z, show the results of the cal. culation according to the rule, taking the same primitive strength for each piece.
1618. After what has been said in a preceding page, it is easy to conceive that the primitive unequal strengths would forin an irregular polygon, whereof each point would answer to a different curve; whilst, supposing the same primitive strength to belong to each piece, there should be an agreement between the strengths and scantlings which constitute a regular curve.
1619. Thus it is to be observed that the points 0 and P of the regular polygon only vary from the regular curve, m, l, k, i, &c., because the ordinate LO is the product of a primitive strength diminished by the mean primitive strength which produced the ordinate of the curve KP. Hence the point P is above the properly correspondent point k.
1620. For the same reason, the point c is above its corresponding point X, because the relative ordinate Cc is the product of a primitive strength greater than the mean which produced the point X.
1621. Referring to the second table, we find that the primitive strength answering to the point O is but 60-76, and the value of the ordinate LO 2502, whilst that of the point P is 68.34, and the value of the ordinate KP 3364; and as the ordinates Ll and Kk corresponding to the curve are calculated upon the same primitive strength of 64.36, which for Ll gives 2726, and for KP 3092: it follows that, in considering all these quantities as equal parts of a similar scale, the point P of the polygon should be (3364–3092=) 272 of these parts above the corresponding point k of the curve, and the point 0 224 of those parts (2726 —2502) below the point l.
1622. To render the researches made, available and useful, the table which follows has been calculated so as to exhibit the greatest strength of beams from pieces 3:198 in. square, up to 19:188 in. by 26 •65 in. The first column contains the length of each piece in English feet. The second column, the proportion of the depth to the length; and The third, the greatest strength of each piece in pounds avoirdupois.
The table is for oak; and it is to be recollected that the weight is supposed to be concentred in the middle of the bearing of the beams, and hence double what it would be if distributed over the whole length of each piece.
Experience, as well as investigation of the experiments, shows, that in order to resist all the efforts and strains which, in practice, timber has to encounter, the weight with which it is loaded ought to be very much less than its breaking weight, and that it ought not to be more than one tenth of what is given as the breaking weight in the following table, beyond which it would not be safe to trust it. The abstraction of the last figure on the right hand, therefore, gives the practicable strength by simple inspection. In a subscquent page, the reduction of the strength of oak to fir, which is in more general use in this country, will be introduced, so as to make the table of more general utility.
TABLE VI. Showing the greatest Strength of Oak Timber lying horizontally, in pounds avoirdupois.
Length of Propor: Breaking Length of Propor: Breaking Length of Propor- Breaking each Piece tion of Weight in each Piece tion of Weight in each Piece tion of Weight in In English Depth to lbs. avoir in English Depth to lbs.avoir in English Depth to lbs.avoir
Feet. Length, dupois. Feet. Length. dupois. Feet. Length. dupois.
Length of Propor. Breaking | Length of Propor. Breaking Length of Propor. Breaking each Piece tion of Weight in cach Piece tion of Weight in each Piece tion of Weight in in English Depth to Ibs.avoir in English Depth to Ibs.avoir in English Depth to Ibs.avoir
Feet. Length. dupois. Feet. Length. dupois. Feet. Length. dupois.