The Mechanical Properties of Wood Part 18

Air-dry specimens will be dipped in water and then wiped dry after the first weighing and just before being immersed for weighing their displacement. All displacement determinations will be made as quickly as possible in order to minimize the absorption of water by the specimen.

STRENGTH VALUES FOR STRUCTURAL TIMBERS

(From Cir. 189, U.S. Forest Service)

The following tables bring together in condensed form the average strength values resulting from a large number of tests made by the Forest Service on the princ.i.p.al structural timbers of the United States. These results are more completely discussed in other publications of the Service, a list of which is given in BIBLIOGRAPHY, PART III.

The tests were made at the laboratories of the U.S. Forest Service, in cooperation with the following inst.i.tutions: Yale Forest School, Purdue University, University of California, University of Oregon, University of Was.h.i.+ngton, University of Colorado, and University of Wisconsin.

Tables XVIII and XIX give the average results obtained from tests on green material, while Tables XX and XXI give average results from tests on air-seasoned material. The small specimens, which were invariably 2" X 2" in cross section, were free from defects such as knots, checks, and cross grain; all other specimens were representative of material secured in the open market. The relation of stresses developed in different structural forms to those developed in the small clear specimens is shown for each factor in the column headed "Ratio to 2" X 2"." Tests to determine the mechanical properties of different species are often confined to small, clear specimens. The ratios included in the tables may be applied to such results in order to approximate the strength of the species in structural sizes, and containing the defects usually encountered, when tests on such forms are not available.

A comparison of the results of tests on seasoned material with those from tests on green material shows that, without exception, the strength of the 2" X 2" specimens is increased by lowering the moisture content, but that increase in strength of other sizes is much more erratic. Some specimens, in fact, show an apparent loss in strength due to seasoning. If structural timbers are seasoned slowly, in order to avoid excessive checking, there should be an increase in their strength. In the light of these facts it is not safe to base working stresses on results secured from any but green material. For a discussion of factors of safety and safe working stresses for structural timbers see the Manual of the American Railway Engineering a.s.sociation, Chicago, 1911. A table from that publication, giving working unit stresses for structural timber, is reproduced in this book, see Table XXII.

|-----------------------------------------------------------------------------------------------------------------------------------| | TABLE XVIII TABLE XVIII | |-----------------------------------------------------------------------------------------------------------------------------------| | BENDING TESTS ON GREEN MATERIAL | |-----------------------------------------------------------------------------------------------------------------------------------| | | Sizes | | | | F.S. at E.L. | M. of R. | M. of E. | Calculated | | |-----------------| Num- | Per | Rings | | | | shear | | Species | | | ber | cent | per |-----------------+-----------------+-----------------+-----------------| | | Cross | Span | of | mois- | inch | Average | Ratio | Average | Ratio | Average | Ratio | Average | Ratio | | | Section | | tests | ture | | per sq. | to 2" | per sq. | to 2" | per sq. | to 2" | per sq. | to 2" | | | | | | | | inch | by 2" | inch | by 2" | inch | by 2" | inch | by 2" | |-----------------+----------+------+-------+-------+-------+---------+-------+---------+-------+---------+-------+---------+-------| | | | | | | | | | | | 1,000 | | | | | | Inches | Ins. | | | | Lbs. | | Lbs. | | lbs. | | Lbs. | | | | | | | | | | | | | | | | | | Longleaf pine | 12 by 12 | 138 | 4 | 28.6 | 9.7 | 4,029 | 0.83 | 6,710 | 0.74 | 1,523 | 0.99 | 261 | 0.86 | | | 10 by 16 | 168 | 4 | 26.8 | 16.7 | 6,453 | .85 | 6,453 | .71 | 1,626 | 1.05 | 306 | 1.01 | | | 8 by 16 | 156 | 7 | 28.4 | 14.6 | 3,147 | .64 | 5,439 | .60 | 1,368 | .89 | 390 | 1.29 | | | 6 by 16 | 132 | 1 | 40.3 | 21.8 | 4,120 | .83 | 6,460 | .71 | 1,190 | .77 | 378 | 1.25 | | | 6 by 10 | 180 | 1 | 31.0 | 6.2 | 3,580 | .72 | 6,500 | .72 | 1,412 | .92 | 175 | .58 | | | 6 by 8 | 180 | 2 | 27.0 | 8.2 | 3,735 | .75 | 5,745 | .63 | 1,282 | .83 | 121 | .40 | | | 2 by 2 | 30 | 15 | 33.9 | 14.1 | 4,950 | 1.00 | 9,070 | 1.00 | 1,540 | 1:00 | 303 | 1.00 | | Douglas fir | 8 by 16 | 180 | 191 | 31.5 | 11.0 | 3,968 | .76 | 5,983 | .72 | 1,517 | .95 | 269 | .81 | | | 5 by 8 | 180 | 84 | 30.1 | 10.8 | 3,693 | .71 | 5,178 | .63 | 1,533 | .96 | 172 | .52 | | | 2 by 12 | 180 | 27 | 35.7 | 20.3 | 3,721 | .71 | 5,276 | .64 | 1,642 | 1.03 | 256 | .77 | | | 2 by 10 | 180 | 26 | 32.9 | 21.6 | 3,160 | .60 | 4,699 | .57 | 1,593 | 1.00 | 189 | .57 | | | 2 by 8 | 180 | 29 | 33.6 | 17.6 | 3,593 | .69 | 5,352 | .65 | 1,607 | 1.01 | 171 | .51 | | | 2 by 2 | 24 | 568 | 30.4 | 11.6 | 5,227 | 1.00 | 9,070 | 1.00 | 1,540 | 1.00 | 303 | 1.00 | | Douglas fir | | | | | | | | | | | | | | | (fire-killed) | 8 by 16 | 180 | 30 | 36.8 | 10.9 | 3,503 | .80 | 4,994 | .64 | 1,531 | .94 | 330 | 1.19 | | | 2 by 12 | 180 | 32 | 34.2 | 17.7 | 3,489 | .80 | 5,085 | .66 | 1,624 | .99 | 247 | .89 | | | 2 by 10 | 180 | 32 | 38.9 | 18.1 | 3,851 | .88 | 5,359 | .69 | 1,716 | 1.05 | 216 | .78 | | | 2 by 8 | 180 | 31 | 37.0 | 15.7 | 3,403 | .78 | 5,305 | .68 | 1,676 | 1.02 | 169 | .61 | | | 2 by 2 | 30 | 290 | 33.2 | 17.2 | 4,360 | 1.00 | 7,752 | 1.00 | 1,636 | 1.00 | 277 | 1.00 | | Shortleaf pine | 8 by 16 | 180 | 12 | 39.5 | 12.1 | 3,185 | .73 | 5,407 | .70 | 1,438 | 1.03 | 362 | 1.40 | | | 8 by 14 | 180 | 12 | 45.8 | 12.7 | 3,234 | .74 | 5,781 | .75 | 1,494 | 1.07 | 338 | 1.31 | | | 8 by 12 | 180 | 24 | 52.2 | 11.8 | 3,265 | .75 | 5,503 | .71 | 1,480 | 1.06 | 277 | 1.07 | | | 5 by 8 | 180 | 24 | 47.8 | 11.5 | 3,519 | .81 | 5,732 | .74 | 1,485 | 1.06 | 185 | .72 | | | 2 by 2 | 30 | 254 | 51.7 | 13.6 | 4,350 | 1.00 | 7,710 | 1.00 | 1,395 | 1.00 | 258 | 1.00 | | Western larch | 8 by 16 | 180 | 32 | 51.0 | 25.3 | 3,276 | .77 | 4,632 | .64 | 1,272 | .97 | 298 | 1.11 | | | 8 by 12 | 180 | 30 | 50.3 | 23.2 | 3,376 | .79 | 5,286 | .73 | 1,331 | 1.02 | 254 | .94 | | | 5 by 8 | 180 | 14 | 56.0 | 25.6 | 3,528 | .83 | 5,331 | .74 | 1,432 | 1.09 | 169 | .63 | | | 2 by 2 | 28 | 189 | 46.2 | 26.2 | 4,274 | 1.00 | 7,251 | 1.00 | 1,310 | 1.00 | 269 | 1.00 | | Loblolly pine | 8 by 16 | 180 | 17 | 15.8 | 6.1 | 3,094 | .75 | 5,394 | .69 | 1,406 | .98 | 383 | 1.44 | | | 5 by 12 | 180 | 94 | 60.9 | 5.9 | 3,030 | .74 | 5,028 | .64 | 1,383 | .96 | 221 | .83 | | | 2 by 2 | 30 | 44 | 70.9 | 5.4 | 4,100 | 1.00 | 7,870 | 1.00 | 1,440 | 1.00 | 265 | 1.00 | | Tamarack | 6 by 12 | 162 | 15 | 57.6 | 16.6 | 2,914 | .75 | 4,500 | .66 | 1,202 | 1.05 | 255 | 1.11 | | | 4 by 10 | 162 | 15 | 43.5 | 11.4 | 2,712 | .70 | 4,611 | .68 | 1,238 | 1.08 | 209 | .91 | | | 2 by 2 | 30 | 82 | 38.8 | 14.0 | 3,875 | 1.00 | 6,820 | 1.00 | 1,141 | 1.00 | 229 | 1.00 | | Western hemlock | 8 by 16 | 180 | 39 | 42.5 | 15.6 | 3,516 | .80 | 5,296 | .73 | 1,445 | 1.01 | 261 | .92 | | | 2 by 2 | 28 | 52 | 51.8 | 12.1 | 4.406 | 1.00 | 7,294 | 1.00 | 1,428 | 1.00 | 284 | 1.00 | | Redwood | 8 by 16 | 180 | 14 | 86.5 | 19.9 | 3,734 | .79 | 4,492 | .64 | 1,016 | .96 | 300 | 1.21 | | | 6 by 12 | 180 | 14 | 87.3 | 17.8 | 3,787 | .80 | 4,451 | .64 | 1,068 | 1.00 | 224 | .90 | | | 7 by 9 | 180 | 14 | 79.8 | 16.7 | 4,412 | .93 | 5,279 | .76 | 1,324 | 1.25 | 199 | .80 | | | 3 by 14 | 180 | 13 | 86.1 | 23.7 | 3,506 | .74 | 4,364 | .62 | 947 | .89 | 255 | 1.03 | | | 2 by 12 | 180 | 12 | 70.9 | 18.6 | 3,100 | .65 | 3,753 | .54 | 1,052 | .99 | 187 | .75 | | | 2 by 10 | 180 | 13 | 55.8 | 20.0 | 3,285 | .69 | 4,079 | .58 | 1,107 | 1.04 | 169 | .68 | | | 2 by 8 | 180 | 13 | 63.8 | 21.5 | 2,989 | .63 | 4,063 | .58 | 1,141 | 1.08 | 134 | .54 | | | 2 by 2 | 28 | 157 | 75.5 | 19.1 | 4,750 | 1.00 | 6,980 | 1.00 | 1,061 | 1.00 | 248 | 1.00 | | Norway pine | 6 by 12 | 162 | 15 | 50.3 | 12.5 | 2,305 | .82 | 3,572 | .69 | 987 | 1.03 | 201 | 1.17 | | | 4 by 12 | 162 | 18 | 47.9 | 14.7 | 2,648 | .94 | 4,107 | .79 | 1,255 | 1.31 | 238 | 1.38 | | | 4 by 10 | 162 | 16 | 45.7 | 13.3 | 2,674 | .95 | 4,205 | .81 | 1,306 | 1.36 | 198 | 1.15 | | | 2 by 2 | 30 | 133 | 32.3 | 11.4 | 2,808 | 1.00 | 5,173 | 1.00 | 960 | 1.00 | 172 | 1.00 | | Red spruce | 2 by 10 | 144 | 14 | 32.5 | 21.9 | 2,394 | .66 | 3,566 | .60 | 1,180 | 1.02 | 181 | .80 | | | 2 by 2 | 26 | 60 | 37.3 | 21.3 | 3,627 | 1.00 | 5,900 | 1.00 | 1,157 | 1.00 | 227 | 1.00 | | White spruce | 2 by 10 | 144 | 16 | 40.7 | 9.3 | 2,239 | .72 | 3,288 | .63 | 1,081 | 1.08 | 166 | .83 | | | 2 by 2 | 26 | 83 | 58.3 | 10.2 | 3.090 | 1.00 | 5,185 | 1.00 | 998 | 1.00 | 199 | 1.00 | |-----------------------------------------------------------------------------------------------------------------------------------| | _Note.--Following is an explanation of the abbreviations used in the foregoing tables:_ | | F.S. at E.L. = Fiber stress at elastic limit. | | M. of E. = Modulus of elasticity. | | M. of R. = Modulus of rupture. | | Cr. str. at E.L. = Crus.h.i.+ng strength at elastic limit. | | Cr. str. at max. ld. = Crus.h.i.+ng strength at maximum load. | |-----------------------------------------------------------------------------------------------------------------------------------|

|-----------------------------------------------------------------------------------------------------------------------------------------------| | TABLE XIX TABLE XIX | |-----------------------------------------------------------------------------------------------------------------------------------------------| | COMPRESSION AND SHEAR TESTS ON GREEN MATERIAL | |-----------------------------------------------------------------------------------------------------------------------------------------------| | | Compression | Compression | Shear | | | parallel to grain | perpendicular to grain | | | |------------------------------------------------------+-------------------------------------------+--------------------------| | | | | | Cr. | | Cr. | | | | | Cr. | | | | | Species | | | Per | str. | M. of | str. | | | | Per | str. | | Per | | | | Size of | No. | cent | at | E. | at max. | Stress | | No. | cent | at max. | No. | cent | Shear | | | specimen | of | of | E. L. | per | ld.,. | area | Height | of | of | ld., | of | of | strength | | | | tests | mois- | per | square | per | | | tests | mois- | per | tests | mois- | | | | | | ture | square | inch | square | | | | ture | square | | ture | | | | | | | inch | | inch | | | | | inch | | | | |-----------------+----------+-------+-------+--------+--------+---------+--------+--------+-------+ ------+---------+-------+-------+----------| | | | | | | 1,000 | | | | | | | | | | | | Inches | | | Lbs. | lbs. | Lbs. | Inches | Inches | | | Lbs. | | | Lbs. | | | | | | | | | | | | | | | | | | Longleaf pine | 4 by 4 | 46 | 26.3 | 3,480 | | 4,800 | 4 by 4 | 4 | 22 | 25.3 | 568 | 44 | 21.8 | 973 | | | 2 by 2 | 14 | 34.7 | | | 4,400 | | | | | | | | | | Douglas fir | 6 by 6 | 515 | 30.7 | 2,780 | 1,181 | 3,500 | 4 by 8 | 16 | 259 | 30.3 | 570 | 531 | 29.7 | 765 | | | 5 by 6 | 170 | 30.9 | 2,720 | 2,123 | 3,490 | | | | | | | | | | | 2 by 2 | 902 | 29.8 | 3,500 | 1,925 | 4,030 | | | | | | | | | | Douglas fir | | | | | | | | | | | | | | | | (fire-killed) | 6 by 6 | 108 | 34.8 | 2,620 | 1,801 | 3,290 | 6 by 8 | 16 | 24 | 33.7 | 368 | 77 | 35.8 | 631 | | | 2 by 2 | 204 | 37.9 | | | 3,430 | | | | | | | | | | Shortleaf pine | 6 by 6 | 95 | 41.2 | 2,514 | 1,565 | 3,436 | 5 by 8 | 16 | 12 | 37.7 | 361 | 179 | 47.0 | 704 | | | 5 by 8 | 23 | 43.5 | 2,241 | 1,529 | 3,423 | 5 by 8 | 14 | 12 | 42.8 | 366 | | | | | | 2 by 2 | 281 | 51.4 | | | 3,570 | 5 by 8 | 12 | 24 | 53.0 | 325 | | | | | | | | | | | | 5 by 5 | 8 | 24 | 47.0 | 344 | | | | | | | | | | | | 2 by 2 | 2 | 277 | 48.5 | 400 | | | | | Western larch | 6 by 6 | 107 | 49.1 | 2,675 | 1,575 | 3,510 | 6 by 8 | 16 | 22 | 43.6 | 417 | 179 | 40.7 | 700 | | | 2 by 2 | 491 | 50.6 | 3,026 | 1,545 | 3,696 | 6 by 8 | 12 | 20 | 40.2 | 416 | | | | | | | | | | | | 4 by 6 | 6 | 53 | 52.8 | 478 | | | | | | | | | | | | 4 by 4 | 4 | 30 | 50.4 | 472 | | | | | Loblolly pine | 8 by 8 | 14 | 63.4 | 1,560 | 365 | 2,140 | 8 by 4 | 8 | 16 | 67.2 | 392 | 121 | 83.2 | 630 | | | 4 by 8 | 18 | 60.0 | 2,430 | 691 | 3,560 | 4 by 4 | 8 | 38 | 44.6 | 546 | | | | | | 2 by 2 | 53 | 74.0 | | | 3,240 | | | | | | | | | | Tamarack | 6 by 7 | 4 | 49.9 | 2,332 | 1,432 | 3,032 | | | | | | 24 | 39.2 | 668 | | | 4 by 7 | 6 | 27.7 | 2,444 | 1,334 | 3,360 | | | | | | | | | | | 2 by 2 | 165 | 36.8 | | | 3,190 | | | | | | | | | | Western hemlock | 6 by 6 | 82 | 46.6 | 2,905 | 1,617 | 3,355 | 6 by 4 | 6 | 30 | 48.7 | 434 | 54 | 65.7 | 630 | | | 2 by 2 | 131 | 55.6 | 2,938 | 1,737 | 3,392 | | | | | | | | | | Redwood | 6 by 6 | 34 | 83.6 | 3,194 | 1,240 | 3,882 | 6 by 8 | 16 | 13 | 86.7 | 473 | 148 | 84.2 | 742 | | | 2 by 2 | 143 | 36.8 | 3,490 | 1,222 | 3,980 | 6 by 6 | 12 | 14 | 83.0 | 424 | | | | | | | | | | | | 6 by 7 | 9 | 13 | 74.7 | 477 | | | | | | | | | | | | 6 by 3 | 14 | 13 | 75.6 | 411 | | | | | | | | | | | | 6 by 2 | 12 | 12 | 66.5 | 430 | | | | | | | | | | | | 6 by 2 | 10 | 11 | 55.0 | 423 | | | | | | | | | | | | 6 by 2 | 8 | 12 | 56.7 | 396 | | | | | | | | | | | | 2 by 2 | 2 | 186 | 75.5 | 569 | | | | | Norway pine | 6 by 7 | 5 | 29.0 | 1,928 | 905 | 2,404 | | | | | | 20 | 26.7 | 589 | | | 4 by 7 | 8 | 28.4 | 2,154 | 1,063 | 2,652 | | | | | | | | | | | 2 by 2 | 178 | 26.8 | | | 2,504 | | | | | | | | | | Red spruce | 2 by 2 | 58 | 35.4 | | | 2,750 | 2 by 2 | 2 | 43 | 31.8 | 310 | 30 | 32.0 | 758 | | White spruce | 2 by 2 | 84 | 61.0 | | | 2,370 | 2 by 2 | 2 | 46 | 50.4 | 270 | 40 | 58.0 | 651 | |-----------------------------------------------------------------------------------------------------------------------------------------------| | _Note.--Following is an explanation of the abbreviations used in the foregoing tables:_ | | F.S. at E.L. = Fiber stress at elastic limit. | | M. of E. = Modulus of elasticity. | | M. of R. = Modulus of rupture. | | Cr. str. at E.L. = Crus.h.i.+ng strength at elastic limit. | | Cr. str. at max. ld. = Crus.h.i.+ng strength at maximum load. | |-----------------------------------------------------------------------------------------------------------------------------------------------|

|-----------------------------------------------------------------------------------------------------------------------------------| | TABLE XX TABLE XX | |-----------------------------------------------------------------------------------------------------------------------------------| | BENDING TESTS ON AIR-SEASONED MATERIAL | |-----------------------------------------------------------------------------------------------------------------------------------| | | Sizes | | | | F.S. at E.L. | M. of R. | M. of E. | Calculated | | |-----------------| Num- | Per | Rings | | | | shear | | Species | | | ber | cent | per |-----------------+-----------------+-----------------+-----------------| | | Cross | Span | of | mois- | inch | Average | Ratio | Average | Ratio | Average | Ratio | Average | Ratio | | | Section | | tests | ture | | per sq. | to 2" | per sq. | to 2" | per sq. | to 2" | per sq. | to 2" | | | | | | | | inch | by 2" | inch | by 2" | inch | by 2" | inch | by 2" | |-----------------+----------+------+-------+-------+-------+---------+-------+---------+-------+---------+-------+---------+-------| | | | | | | | | | | | 1,000 | | | | | | Inches | Ins. | | | | Lbs. | | Lbs. | | lbs. | | Lbs. | | | | | | | | | | | | | | | | | | Longleaf pine | 8 by 16 | 180 | 5 | 22.2 | 16.0 | 3,390 | 0.50 | 4,274 | 0.37 | 1,747 | 1.00 | 288 | 0.75 | | | 6 by 16 | 132 | 1 | 23.4 | 17.1 | 3,470 | .51 | 6,610 | .57 | 1,501 | .86 | 388 | 1.01 | | | 6 by 10 | 177 | 2 | 19.0 | 8.8 | 4,560 | .68 | 7,880 | .68 | 1,722 | .99 | 214 | .56 | | | 4 by 11 | 180 | 1 | 18.4 | 23.9 | 3,078 | .46 | 8,000 | .69 | 1,660 | .95 | 251 | .66 | | | 6 by 8 | 177 | 6 | 20.0 | 13.7 | 4,227 | .63 | 8,196 | .71 | 1,634 | .94 | 177 | .46 | | | 2 by 2 | 30 | 17 | 15.9 | 13.9 | 6,750 | 1.00 | 11,520 | 1.00 | 1,740 | 1.00 | 383 | 1.00 | | Douglas fir | 8 by 16 | 180 | 91 | 20.8 | 13.1 | 4,563 | .68 | 6,372 | .61 | 1,549 | .91 | 269 | .64 | | | 5 by 8 | 180 | 30 | 14.9 | 12.2 | 5,065 | .76 | 6,777 | .65 | 1,853 | 1.09 | 218 | .52 | | | 2 by 2 | 24 | 211 | 19.0 | 16.4 | 6,686 | 1.00 | 10,378 | 1.00 | 1,695 | 1.00 | 419 | 1.00 | | Shortleaf pine | 8 by 16 | 180 | 3 | 17.0 | 12.3 | 4,220 | .54 | 6,030 | .50 | 1,517 | .85 | 398 | .98 | | | 8 by 14 | 180 | 3 | 16.0 | 12.3 | 4,253 | .55 | 5,347 | .44 | 1,757 | .98 | 307 | .76 | | | 8 by 12 | 180 | 7 | 16.0 | 12.4 | 5,051 | .65 | 7,331 | .60 | 1,803 | 1.01 | 361 | .89 | | | 5 by 8 | 180 | 6 | 12.2 | 22.5 | 7,123 | .92 | 9,373 | .77 | 1,985 | 1.11 | 301 | .74 | | | 2 by 2 | 30 | 67 | 14.2 | 13.7 | 7,780 | 1.00 | 12,120 | 1.00 | 1,792 | 1.00 | 404 | 1.00 | | Western larch | 8 by 16 | 180 | 23 | 18.3 | 21.9 | 3,343 | .57 | 5,440 | .53 | 1,409 | .90 | 349 | .96 | | | 8 by 12 | 180 | 29 | 17.8 | 23.4 | 3,631 | .62 | 6,186 | .60 | 1,549 | .99 | 295 | .81 | | | 5 by 8 | 180 | 10 | 13.6 | 27.6 | 4,730 | .80 | 7,258 | .71 | 1,620 | 1.04 | 221 | .61 | | | 2 by 2 | 30 | 240 | 16.1 | 26.8 | 5,880 | 1.00 | 10,254 | 1.00 | 1,564 | 1.00 | 364 | 1.00 | | Loblolly pine | 8 by 16 | 180 | 14 | 20.5 | 7.4 | 4,195 | .81 | 6,734 | .72 | 1,619 | 1.10 | 462 | 1.45 | | | 6 by 16 | 126 | 4 | 20.2 | 5.0 | 2,432 | .47 | 4,295 | .46 | 1,324 | .90 | 266 | .84 | | | 6 by 10 | 174 | 3 | 21.3 | 4.7 | 3,100 | .60 | 6,167 | .66 | 1,449 | .99 | 173 | .54 | | | 4 by 12 | 174 | 4 | 19.8 | 4.7 | 2,713 | .52 | 5,745 | .61 | 1,249 | .85 | 185 | .58 | | | 8 by 8 | 180 | 9 | 22.9 | 4.9 | 2,903 | .56 | 4,557 | .48 | 1,136 | .77 | 93 | .29 | | | 6 by 7 | 144 | 2 | 21.1 | 5.0 | 2,990 | .58 | 4,968 | .53 | 1,286 | .88 | 116 | .36 | | | 4 by 8 | 132 | 8 | 19.5 | 9.1 | 3,384 | .65 | 6,194 | .66 | 1,200 | .82 | 196 | .62 | | | 2 by 2 | 30 | 123 | 17.6 | 6.6 | 5,170 | 1.00 | 9,400 | 1.00 | 1,467 | 1.00 | 318 | 1.00 | | Tamarack | 6 by 12 | 162 | 5 | 23.0 | 15.1 | 3,434 | .45 | 5,640 | .43 | 1,330 | .82 | 318 | .75 | | | 4 by 10 | 162 | 4 | 14.4 | 9.7 | 4,100 | .54 | 5,320 | .41 | 1,386 | .84 | 252 | .59 | | | 2 by 2 | 30 | 47 | 11.3 | 16.2 | 7,630 | 1.00 | 13,080 | 1.00 | 1,620 | 1.00 | 425 | 1.00 | | Western hemlock | 8 by 16 | 180 | 44 | 17.7 | 17.8 | 4,398 | .69 | 6,420 | .62 | 1,737 | 1.04 | 406 | 1.06 | | | 2 by 2 | 28 | 311 | 17.9 | 19.4 | 6,333 | 1.00 | 10,369 | 1.00 | 1,666 | 1.00 | 382 | 1.00 | | Redwood | 8 by 16 | 180 | 6 | 26.3 | 22.4 | 3,797 | .79 | 4,428 | .57 | 1,107 | .96 | 294 | 1.05 | | | 6 by 12 | 180 | 6 | 16.1 | 17.7 | 3,175 | .66 | 3,353 | .43 | 728 | .64 | 167 | .60 | | | 7 by 9 | 180 | 6 | 15.9 | 15.2 | 3,280 | .69 | 4,002 | .51 | 1,104 | .96 | 147 | .53 | | | 3 by 14 | 180 | 6 | 13.1 | 24.4 | | | 5,033 | .64 | | | 291 | 1.04 | | | 2 by 12 | 180 | 5 | 13.8 | 14.4 | 3,928 | .82 | 5,336 | .68 | 1,249 | 1.09 | 260 | .93 | | | 2 by 10 | 180 | 5 | 13.8 | 24.8 | 3,757 | .79 | 4,606 | .59 | 1,198 | 1.05 | 186 | .67 | | | 2 by 8 | 180 | 6 | 13.7 | 20.7 | 4,314 | .90 | 5,050 | .65 | 1,313 | 1.15 | 166 | .60 | | | 2 by 2 | 28 | 122 | 15.2 | 18.8 | 4,777 | 1.00 | 7,798 | 1.00 | 1,146 | 1.00 | 279 | 1.00 | | Norway pine | 6 by 12 | 162 | 5 | 16.7 | 8.1 | 2,968 | .56 | 5,204 | .61 | 1,123 | .97 | 286 | 1.02 | | | 4 by 10 | 162 | 5 | 13.7 | 12.0 | 5,170 | .98 | 6,904 | .82 | 1,712 | 1.48 | 317 | 1.13 | | | 2 by 2 | 30 | 60 | 14.9 | 11.2 | 5,280 | 1.00 | 8,470 | 1.00 | 1,158 | 1.00 | 281 | 1.00 | |-----------------------------------------------------------------------------------------------------------------------------------| | _Note.--Following is an explanation of the abbreviations used in the foregoing tables:_ | | F.S. at E.L. = Fiber stress at elastic limit. | | M. of E. = Modulus of elasticity. | | M. of R. = Modulus of rupture. | | Cr. str. at E.L. = Crus.h.i.+ng strength at elastic limit. | | Cr. str. at max. ld. = Crus.h.i.+ng strength at maximum load. | |-----------------------------------------------------------------------------------------------------------------------------------|

|-----------------------------------------------------------------------------------------------------------------------------------------------| | TABLE XXI TABLE XXI | |-----------------------------------------------------------------------------------------------------------------------------------------------| | COMPRESSION AND SHEAR TESTS ON AIR-SEASONED MATERIAL | |-----------------------------------------------------------------------------------------------------------------------------------------------| | | Compression | Compression | Shear | | | parallel to grain | perpendicular to grain | | | |------------------------------------------------------+-------------------------------------------+--------------------------| | | | | | Cr. | | Cr. | | | | | Cr. | | | | | Species | | | Per | str. | M. of | str. | | | | Per | str. | | Per | | | | Size of | No. | cent | at | E. | at max. | Stress | | No. | cent | at max. | No. | cent | Shear | | | specimen | of | of | E. L. | per | ld.,. | area | Height | of | of | ld., | of | of | strength | | | | tests | mois- | per | square | per | | | tests | mois- | per | tests | mois- | | | | | | ture | square | inch | square | | | | ture | square | | ture | | | | | | | inch | | inch | | | | | inch | | | | |-----------------+----------+-------+-------+--------+--------+---------+--------+--------+-------+ ------+---------+-------+-------+----------| | | | | | | 1,000 | | | | | | | | | | | | Inches | | | Lbs. | lbs. | Lbs. | Inches | Inches | | | Lbs. | | | Lbs. | | | | | | | | | | | | | | | | | | Longleaf pine | 4 by 5 | 46 | 26.3 | 3,480 | | 4,800 | 4 by 5 | 4 | 22 | 25.1 | 572 | 52 | 20.2 | 984 | | Douglas fir | 6 by 6 | 259 | 20.3 | 3,271 | 1,038 | 4,258 | 4 by 8 | 16 | 44 | 20.8 | 732 | 465 | 22.1 | 822 | | | 2 by 2 | 247 | 18.7 | 3,842 | 1,084 | 5,002 | 4 by 8 | 10 | 32 | 18.1 | 584 | | | | | | | | | | | | 4 by 4 | 8 | 51 | 20.2 | 638 | | | | | | | | | | | | 4 by 4 | 6 | 49 | 24.0 | 613 | | | | | | | | | | | | 4 by 4 | 4 | 29 | 24.8 | 603 | | | | | Shortleaf pine | 6 by 6 | 29 | 15.7 | 4,070 | 1,951 | 6,030 | 8 by 5 | 16 | 4 | 17.8 | 725 | 85 | | 1,135 | | | 2 by 2 | 57 | 14.2 | | | 6,380 | 8 by 5 | 14 | 3 | 16.3 | 757 | | | | | | | | | | | | 8 by 5 | 12 | 5 | 15.1 | 730 | | | | | | | | | | | | 5 by 5 | 8 | 6 | 13.0 | 918 | | | | | | | | | | | | 2 by 2 | 2 | 57 | 13.9 | 926 | | | | | Western larch | 6 by 6 | 112 | 16.0 | | | 5,445 | 8 by 6 | 16 | 17 | 18.8 | 491 | 193 | 15.0 | 905 | | | 4 by 4 | 81 | 14.7 | | | 6,161 | 8 by 6 | 12 | 18 | 17.6 | 526 | | | | | | 2 by 2 | 270 | 14.8 | | | 5,934 | 5 by 4 | 8 | 22 | 13.3 | 735 | | | | | Loblolly pine | 6 by 6 | 23 | | 3,357 | 1,693 | 5,005 | 8 by 5 | 16 | 12 | 19.8 | 602 | 156 | 11.3 | 1,115 | | | 5 by 5 | 10 | 22.4 | 2,217 | 545 | 2,950 | 8 by 5 | 8 | 7 | 22.9 | 679 | | | | | | 4 by 8 | 8 | 19.4 | 3,010 | 633 | 3,920 | 4 by 5 | 8 | 8 | 19.5 | 715 | | | | | | 2 by 2 | 69 | | | | 5,547 | | | | | | | | | | Tamarack | 6 by 7 | 3 | 15.7 | 2,257 | 1,042 | 3,323 | 2 by 2 | 2 | 57 | 16.2 | 697 | 60 | 14.0 | 879 | | | 4 by 7 | 3 | 13.6 | 3,780 | 1,301 | 4,823 | | | | | | | | | | | 4 by 4 | 57 | 14.9 | 3,386 | 1,353 | 4,346 | | | | | | | | | | | 2 by 2 | 66 | 14.6 | | | 4,790 | | | | | | | | | | Western hemlock | 6 by 6 | 102 | 18.6 | 4,840 | 2,140 | 5,814 | 7 by 6 | 15 | 25 | 18.2 | 514 | 131 | 17.7 | 924 | | | 2 by 2 | 463 | 17.0 | 4,560 | 1,923 | 5,403 | 6 by 6 | 6 | 26 | 16.8 | 431 | | | | | | | | | | | | 4 by 4 | 4 | 6 | 15.9 | 488 | | | | | Redwood | 6 by 6 | 18 | 16.9 | | | 4,276 | 8 by 6 | 16 | 5 | 25.4 | 548 | 95 | 12.4 | 671 | | | 2 by 2 | 115 | 14.6 | | | 5,119 | 6 by 6 | 12 | 6 | 14.7 | 610 | | | | | | | | | | | | 7 by 6 | 9 | 5 | 14.8 | 500 | | | | | | | | | | | | 3 by 6 | 14 | 2 | 12.6 | 470 | | | | | | | | | | | | 2 by 6 | 12 | 2 | 16.2 | 498 | | | | | | | | | | | | 2 by 6 | 10 | 4 | 14.3 | 511 | | | | | | | | | | | | 2 by 6 | 8 | 2 | 13.2 | 429 | | | | | | | | | | | | 2 by 2 | 2 | 145 | 13.8 | 564 | | | | | Norway pine | 6 by 7 | 4 | 15.2 | 2,670 | 1,182 | 4,212 | 2 by 2 | 2 | 36 | 10.0 | 924 | 44 | 11.9 | 1,145 | | | 4 by 7 | 2 | 22.2 | 3,275 | 1,724 | 4,575 | | | | | | | | | | | 4 by 4 | 55 | 16.6 | 3,048 | 1,367 | 4,217 | | | | | | | | | | | 2 by 2 | 44 | 11.2 | | | 7,550 | | | | | | | | | |-----------------------------------------------------------------------------------------------------------------------------------------------| | _Note.--Following is an explanation of the abbreviations used in the foregoing tables:_ | | F.S. at E.L. = Fiber stress at elastic limit. | | M. of E. = Modulus of elasticity. | | M. of R. = Modulus of rupture. | | Cr. str. at E.L. = Crus.h.i.+ng strength at elastic limit. | | Cr. str. at max. ld. = Crus.h.i.+ng strength at maximum load. | |-----------------------------------------------------------------------------------------------------------------------------------------------|

|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | TABLE XXII TABLE XXII | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [b]WORKING UNIT-STRESSES FOR STRUCTURAL TIMBER[c] | | EXPRESSED IN POUNDS PER SQUARE INCH | | (From Manual of the American Railway Engineering a.s.sn., 1911, p. 153) | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | NOTE.--The working unit-stresses given in the table are intended for railroad bridges and trestles. For highway bridges and trestles the unit-stresses may be increased | | twenty-five (25) per cent. For buildings and similar structures, in which the timber is protected from the weather and practically free from impact, the unit-stresses may be | | increased fifty (50) per cent. To compute the deflection of a beam under long-continued loading instead of that when the load is first applied, only fifty (50) per cent of the | | corresponding modulus of elasticity given in the table is to be employed. | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | | BENDING | SHEARING | COMPRESSION | | | |---------------------------------+-----------------------------------------+-------------------------------------------------------------------------| Ratio | | | Extreme | Modulus of | Parallel to | Longitudinal | Perpendicular | Parallel to | For | Formulae for | of | | | fibre | elasticity | the grain | shear in | to the grain | the grain | columns | working stress in | length | | KIND OF | stress | | | beams | | | under 15 | long columns over | of | | TIMBER |--------------------+------------+--------------------+--------------------+--------------------+--------------------| diameters | 15 diameters | stringer | | | Average | Working | | Average | Working | Elastic | Working | Elastic | Working | Average | Working | working | | to | | | ultimate | stress | Average | ultimate | stress | limit | stress | limit | stress | ultimate | stress | stress | | depth | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Douglas fir | 6100 | 1200 | 1,510,000 | 690 | 170 | 270 | 110 | 630 | 310 | 3600 | 1200 | 900 | 1200(1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Longleaf pine | 6500 | 1300 | 1,610,000 | 720 | 180 | 300 | 120 | 520 | 260 | 3800 | 1300 | 980 | 1300(1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Shortleaf pine | 5600 | 1100 | 1,480,000 | 710 | 170 | 330 | 130 | 340 | 170 | 3400 | 1100 | 830 | 1100(1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | White pine | 4400 | 900 | 1,130,000 | 400 | 100 | 180 | 70 | 290 | 150 | 3000 | 1000 | 750 | 1000(1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Spruce | 4800 | 1000 | 1,310,000 | 600 | 150 | 170 | 70 | 370 | 180 | 3200 | 1100 | 830 | 1100(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Norway pine | 4200 | 800 | 1,190,000 | 590[d] | 130 | 250 | 100 | | 150 | 2600[d] | 800 | 600 | 800(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Tamarack | 4600 | 900 | 1,220,000 | 670 | 170 | 260 | 100 | | 220 | 3200[d] | 1000 | 750 | 1000(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Western hemlock | 5800 | 1100 | 1,480,000 | 630 | 160 | 270[d] | 100 | 440 | 220 | 3500 | 1200 | 900 | 1200(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Redwood | 5000 | 900 | 800,000 | 300 | 80 | | | 400 | 150 | 3300 | 900 | 680 | 900(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Bald cypress | 4800 | 900 | 1,150,000 | 500 | 120 | | | 340 | 170 | 3900 | 1100 | 830 | 1100(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Red cedar | 4200 | 800 | 800,000 | | | | | 470 | 230 | 2800 | 900 | 680 | 900(1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | White oak | 5700 | 1100 | 1,150,000 | 840 | 210 | 270 | 110 | 920 | 450 | 3500 | 1300 | 980 | 1300(1-_l_/60_d_) | 12 | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | These unit-stresses are for a green condition of timber and are _l_ = Length in inches. | | to be used without increasing the live load stresses for impact. _d_ = Least side in inches. | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| |[Footnote b: Adopted, Vol. 1909, pp. 537, 564, 609-611.] | |[Footnote c: Green timber in exposed work.] | |[Footnote d: Partially air-dry] | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

BIBLIOGRAPHY

Part I: Some general works on mechanics, materials of construction, and testing of materials.

Part II: Publications and articles on the mechanical properties of wood, and timber testing.

Part III: Publications of the U.S. Government on the mechanical properties of wood, and timber testing.

PART 1. SOME GENERAL WORKS ON MECHANICS, MATERIALS OF CONSTRUCTION, AND TESTING OF MATERIALS

ALLAN, WILLIAM: Strength of beams under transverse loads. New York, 1893.

ANDERSON, SIR JOHN: The strength of materials and structures.

London, 1902.

BARLOW, PETER: Strength of materials, 1st ed. 1817; rev. 1867.

BURR, WILLIAM H.: The elasticity and resistance of the materials of engineering. New York, 1911.

CHURCH, IRVING P.: Mechanics of engineering. New York, 1911.

HATFIELD, R.G.: Theory of transverse strain. 1877.

HATT, W.K., and SCOFIELD, H.H.: Laboratory manual of testing materials. New York, 1913.

JAMESON, J.M.: Exercises in mechanics. (Wiley technical series.) New York, 1913.

JAMIESON, ANDREW: Strength of materials. (Applied mechanics and mechanical engineering, Vol. II.) London, 1911.

JOHNSON, J.B.: The materials of construction. New York, 1910.

KENT, WILLIAM: The strength of materials. New York, 1890.

KOTTCAMP, J.P.: Exercises for the applied mechanics laboratory.

(Wiley technical series.) New York, 1913.

LANZA, GAETANO: Applied mechanics. New York, 1901.

MERRIMAN, MANSFIELD: Mechanics of materials. New York, 1912.

MURDOCK, H.E.: Strength of materials. New York, 1911.

RANKINE, WILLIAM J.M.: A manual of applied mechanics. London, 1901.

THIL, A.: Conclusion de l'etude presentee a la Commission des methodes d'essai des materiaux de construction. Paris, 1900.

THURSTON, ROBERT H.: A treatise on non-metallic materials of engineering: stone, timber, fuel, lubricants, etc. (Materials of engineering, Part I.) New York, 1899.

UNWIN, WILLIAM C.: The testing of materials of construction.

London, 1899.

WATERBURY, L.A.: Laboratory manual for testing materials of construction. New York, 1912.

WOOD, DEVOLSON: A treatise on the resistance of materials. New York, 1897.

PART II. PUBLICATIONS AND ARTICLES ON THE MECHANICAL PROPERTIES OF WOOD, AND TIMBER TESTING

ABBOT, ARTHUR V.: Testing machines, their history, construction and use. Van Nostrand's Eng. Mag., Vol. x.x.x, 1884, pp. 204-214; 325-344; 382-397; 477-490.

ADAMS, E.E.: Tests to determine the strength of bolted timber joints. Cal. Jour, of Technology, Sept., 1904.

ALVAREZ, ARTHUR C.: The strength of long seasoned Douglas fir and redwood. Univ. of Cal. Pub. in Eng., Vol. I, No. 2, Berkeley, 1913, pp. 11-20.