Rocky Mountain mine timbers
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2B.) Usdeardent Oracle
No. 77
Contribution from the Forest Service, Henry S. Graves, Forester.
May 7, 1914, (PROFESSIONAL PAPER.)
Rocky Mountain Mine Timbers.'
By Norman DE W. Betts, Engineer in Forest Products, Forest Products Laboratory.
Strength. Object Of The Tests.
Approximately one-fourth of the timber cut in Colorado during 1911 was consumed by the mining industries of that State. A num- ber of different species are used, and their relative strength is of con- siderable importance both to miners and producers of mine timbers. Native Douglas fir, the so-called ‘‘red spruce” of the Rocky Mountain region, has been the wood most suitable for use in mines, but it is no longer available for a very large part of thesupply. The forests of lodgepole pme and Engelmann spruce, containing also several minor species, must furnish the bulk of the material. The Forest Service, im cooperation with the University of Colorado, has tested these dif- ferent timbers to determine their relative strength.
Since the timbers are used both green and air-dried, the influence of moisture on their strength is of interest, and material was tested in order to bring out this relation.
The relative value of fire-killed timber and of timber cut from growing trees has been the subject of much discussion. Since con- siderable dead timber is used in the mines, and a large supply is avail- able, tests on this kind of material were included, with the idea of determining its strength in the round form for comparison with
material cut green. MATERIAL.
The material tested? consisted of round beams and of props and caps representative of the market run of timber used in the coal mines. The props were from 5 to 6 inches in diameter and 6 feet long; the caps from 5 to 6 inches in diameter and 8 feet long: the beams nomi- nally 8, 10, and 12 inches in diameter and 16 feet long. Table 1 gives a list of the material tested, and shows the form and number of
1 This paper is of interest to miners and producers of mine timbers and will be suitable for distribution in Idaho, Montana, Wyoming, Colorado, Nevada, Arizona, and New Mexico.
2 The material for the tests described in this report was in part donated by the Northern Coal & Coke Co. of Denver and in part obtained from several national forests located in Colorado. The tests were made at
the timber-testing station of the Forest Service, which is conducted in cooperation with the University of Colorado, at Boulder.
29206°—14——1
Bulletin 77, U. S. Department Of Agriculture.
the specimens, the kind of wood, the locality where secured, and the number of the table in which the individual tests are recorded.
Species and form of material.
Eoespole pine (ship-
ment A
Round props
Lodgepole pine (ship- ment B):
Round props
Alpine fir:
Engelmann spruce: Round props
Douglas fir: Round props
Bristle-cone pine: Round props
Western yellow pine (shipment A):
Round props
Western. yellow pine (shipment B):
Round props
TABLE 1.— Material tested.
Individual test
records given in—
Table] Reference No.
Seer
Nos.
ow re
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OO Fee
°
Ore Orr ou ) (om)
ee rey
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Number
of pieces.
Source.
Colo. Probably cut on the west slope of the divide in Colorado.
Do.
r ards of Northern Coal & Coke Co., at Louisville,
ards of Northern Coal & Coke Co. Probably cut on east slope of the divide in Boulder Co., Colo.
Do.
Gunnison National Forest, Colo. (Cut from live timber.)
Gunnison National Forest, Colo. ber standing dead for 30 years.)
Partly from yards of Northern Coal & Coke Co., a5, from Arapahoe National Forest, Colo.
(Cut from tim-
ee from yards of Northern Coal & Coke Co., partly from Pike National Forest, Colo.
Do.
5 eke from yards of Northern Coal & Coke Co.,
partly from Gunnison National Forest. Do.
Pike National Forest, Colo. Do.
Pike National Forest, Colo. Jack.”’)
Do.
(Shipped as “ Black
Partly from yards of Northern Coal & Coke Co., partly from Gunnison National Forest.
Do.
The material from the National Forests was received at the labora-
tory in a green condition.
soaked in water, while others were piled to air-season.
The timbers from the yards of the coal company were partially air-dried. Upon arrival at the testing sta- tion all green material was barked and some of the specimens were
The object
of the water-soaking was to keep the timber in a green condition until tested or, in the case of the dead beams, to increase the moisture content to a point which would enable them to be compared with
green material.
The material cut green and water-soaked is used as
the basis for making the comparisons with air-dry material.
Rocky Mountain Mine Timbers. 3
The water-soaked material was placed in a small pond during the summer months and the first tests were made after 60 days and the last after 125 days of soaking. No means were available to give complete submersion. The caps and props were tied in bundles of five and the beams were rafted, iron rails being used to help submerge a part of the material. At intervals of two or three days the bun- dles and the individual beams were turned to make the soaking as uniform as possible.
Boe ee ae ee el
Lodgepole Pine Abe Shipment -B
Sass en Soe SSS SSS. ’'™onyyy 7634
cobs Paes DOUGLAS FIR ror a7 rT en
ae SG BSG 41323
a aoa a WESTERN YELLOW PINE pee EL SHIPMENT -B
See 2 Lat SSG. N4130S
ie al Perea Ro. ai
iii RX MW SN4122S
Sai EN@ELMANN SPRUCE S RELA an
KSAIR DRY al .. "oI°'"'"F
Pea allies ALPINE FIR
cae SS W009i. 754
ian divas crag ee SHIPMENT -A-
cidehiba aan eee aa
1000 — 2000 at ; ; 5000 CRUSHING STRENGTH AT MAXIMUM LOAD POUNDS PER saan INCH
Bristle Cone Pine
Fie. 1.—Comparison of different species; 6-inch round mine props—air-dried and green. RESULTS OF TESTS.
Summaries of the results of the tests showing the average, maxi- mum, and minimum of each group are presented in Tables 2 (props), 3 (caps), and 4 (beams). Results of the individual tests on the green props are recorded in Table 11, on the air-seasoned props in Table 12, on the caps in Tables 13 and 14, and on the beams in Tables 15 and 16.
Props And Caps.
The relative strength of air-seasoned and green material for each
species and the relative strength of the different species are shown
4 Bulletin 77, U. S. Department Of Agriculture.
graphically in figures 1 and 2. The increase in strength of the props due to seasoning is very evident in each species, and the average strength of the seasoned props of all species is 2.3 times that of the green ones at both maximum load and elastic limit. In the case of the caps the average strength of the dry timbers at the maximum load is 1.6 and at elastic limit 2.2 times the strength of the green timbers. While at the elastic limit the influence of the moisture
Le ne DOUGLAS FIR pee Ga es
Bd:
fee LODGEPOLE PINE CPREBHIEG sal TT ae
WEE LIA QCM oO '=FDn0w>;%*r_®[]°wz_w_ywq] "WK 1° Ott
“Srnunees Bristle-Cone Pine
ESAIR RY, WQ@WCiWiCiCiCOC ee SS. GG 5242 mer eee ENGELMANN SPRUCE ce
Peed 1a BDWG WW
eae eee GREEN rr zs
Kmsaer Dry, Bww, 73 408
eee pale cen ALPINE FIR ct rT]
ali i BCD. 19549
eqs a “SHIPMENT ‘Br cette a RE
Msair_ Dry.
ements WESTER YELLOW PINE KAGREEN Ww jcme ek s ee 1000 S000 9000
2000 3000 gies 5000 6000 7000 MODULUS OF RUPTURE — POUNDS PER SQUARE INCH
Fic. 2.—Comparison of different species; 6-inch round mine caps—air-dried and green.
was practically the same for both the crushing and bending tests, at the maximum load it is much more pronounced in the crushing tests. Stiffness in bending was increased by seasoning to 1.4 times the green value. There appears to be no marked variation in this strength ratio among the various species tested. It is slightly below the average in Douglas fir, due to the consistently high values for the green material in comparison with the other species,
Rocky Mountain Mine Timbers. 5
TABLE 2.—Summary of crushing tests on round mine props (nominal size, 5-inch top by 6 feet long).
Green (Water Soaked).
Diameter. Crushing ‘ Rings strength Eee Modulus Species, number of tests. Moisture.} per at maxi-| 9, elastic Of elas- ache Tope Butt.| cUot limits|) eity-
Lbs. per Lbs. per 1,000 lbs. Lodgepole pine (shipment A); 10tests: Per cent. Inches. Inches. sq. in. sq. in. per sq.in. FAV CRAPO eee tr octet ae es ee (eee 40 5.73 6.18 1, 865 1, 495 599 Maximumes oe. 25 ase eec os oo ese 102.0 56 6.13 6.92 2, 285 1,981 839 Marna WI ape et fe a Sas 48.3 28 4.93 5.33 1, 440 1,049 343 Lodgepole pine (shipment B); 10 tests
WOLARO Rs aeae Sen eee wo ES 70. 8 43 5,90 6. 58 1,605 1,240 496 Maxciin tim Be)ce hee et ae 108. 2 58 7. 00 7. 56 1,890 1,559 621 IMU eee ee tears 2 57.5 31 4.85 6.05 1, 169 866 387
Alpine fir; 9 tests:
VORALO Maas. pce eee SoBe OL: 91.0 26 4.90 5.65 1,920 1, 490 541 Maximnitescencn site be. 4. cess. 123.6 42 5.37 6.05 2,305 1,944 706 Minimise eh poet oa. See es 38.6 13 4.62 5.38 1,573 1, 268 401
Engelmann spruce; 11 tests PAWCLAP Olt ater nee cincil Sects 62.3 32 4.95 5.80 1,750 1, 347 529 Mexauat SE SUS Sar eee 89.1 46 6. 20 7.08 2,115 1,755 686 pa pene ec eyn eet ses 2 Cee 38.1 19 4.14 5.09 1,511 1,062 358 Douglas fir: 10 tests: Average RN ee RANE oat 50.5 39 5.48 6.05 2,580 2, 130 758 Maxdmiiimeges sp eee eee Wares 91.6 76 6. 84 7.16 2,870 2,488 .:- 865 MANIMUINE eee eeyeee acceso ase 2c 30.0 17 4.93 5.41 25 1,885 596 Bristle-cone pine; 10 tests IAWVORAP OMe esos tne eos cee Sas. 85.9 35 4.58 5. 38 1,657 1,310 508 Maxam mess Ae eee es Re SS 109.0 43 5. 33 6. 40 2,026 1,590 638 WY OWavra tbh eee ca) et aa 56.1 31 3.98 4.77 1,364 965 390 Western yellow pine (shipment A); 10 tests: SAV OLA PC lss epee as ha A A 96.1 14 4.44 5. 20 1, 475 1, 201 443 Maxim mas Sone pee ae 116.1 16 4.78 5.60 1,681 1, 412 516 Minimizes eee ee ee cee ase. 83. 2 13 4.14 4.94 1, 269 1,038 345 Western yellow pine ( ShpEahe 1B); 10 tests: POG) EN OBOE bee aR eee 82.0 18 5.35 6. 00 1, 940 1, 450 561 Maxine see ee ee 113.2 32 5. 65 6.17 2, 410 1,883 762 Minium ee eee i eS 54.8 11 5.01 5.73 1, 668 1,182 448 AIR SEASONED. Lodgepole pine (shipment A); 5 tests
WCE SOs coseconuesasee oeECeae neces 11.5 46 4.93 5. 43 4,130 3,513 993 Ma xan et ee 12.3 57 5.17 5.57 4,770 4,190 1,194 BADER TPR asp ore eg ee PI ry 11.0 34 4.77 5.17 3,340 2,750 875
Lodgepole pine (shipmen* B); 5 tests
VOTAg Omer tas see eee anche renee 252 45 4.81 5. 44 5, 568 4, 438 1, 282 IM axa IT ae eel ects ee oe 15.9 50 5. 25 5.73 6, 340 4,980 1, 452 Mannan. 209. ete bo ee 11.0 42) i 4. OL 137-5. 01 4, 980 4,010 1, 135
Alpine fir; 3 tests AV OTAGO meee eee ens eee eens 11.6 18 4.27 5. 28 4,097 3, 530 978 Meixai mises eee ks Mi 12.4 23 4.46 5. 41 4, 260 3,875 1,043 WG EAME TOD oo 5 Sa ee ea a 10.5 15 4.06 5.09 3,910 3, 165 890 Engelmann spruce; 7 tests: AV CLAP OME eee Pes es Ue, 11.8 33 4,42 5. 29 4,122 3, 297 1,042 Ma xaT TT eae eee ee Ee 13.7 50 5.09 5.97 5, 560 4, 290 1,321 MAMTA ee ere eee. Se aie 10.9 16 3.50 4,62 2, 990 2, 410 703 Douglas fir; 5 tests: Average eet cos cee es 12.3 49 4.85 5.33 4, 634 3, 617 1,131 MEST es eee ee IB Bi 76 5.33 6.05 5, 720 4, 450 1,324 pe MUTA Trae rive eae Sate ee 11.5 28 4.30 4.62 2, 960 2,340 873 Bristle-cone pine; 5 tests: ASV OLAGOM mane epee ee at 12.4 38 3.68 4. 44 3,501 2, 823 826 RUTRUL ITI eee ee pee Ee er 12.6 45 3.98 . 4.85 4, 390 3,512 1,023 JN ORGU TCH Da0 si De he Sa a 12.2 30 3.18 4,22 2,340 2,013 628 ten yellow pine (shipment A); INSIGED do Ae OGRE Ses OEE aaa MIA, 14 3.93 4.78 3, 764 3, 401: 887 Se MANIA sss fet 2 13.4 16 4.30 4,85 5, 330 4,780 1, 146 MEU eee en a Ee 10.5 11 3.50 4.62 3,050 2,470 626 Western yellow pine (shipment B); ae Rae Cer g os ek 18 Wz 18 4.82 5.44 4,132 3, 266 956 MaMa a, ere ea Ae ele 13.0 31 4.93 5.65 4,790 3,770 1,160 MTA eee Ree ee OS 10.9 12 4.62 5,25 3,120 2,270 628
6 Bulletin 77, U. S. Department Of Agriculture.
TABLE 3.—Summary of bending tests on round mine caps (nominal size, 5-inch top by 8 feet long; span, 7 feet; third-point loading).
Green (Water Soaked).
Rings Diameter. Modulas Fiber pres Species, number of tests. Moisture.| per of sep P inch. Tupture. Sc Top. Butt. limit. Id.
E ; ese eae age hon a Lodgepole pine (shipment A); 10 z
tests: 4 Per cent. Inches. Inch
es AWETAL OC cer ne see ee ARO 3 43 5.59 6. 20 98.0 Ma xan s 2 See Sf Sie 133.3 61 5.90 6. 68 6, 460 3, 830 119.7 OES Een peers 56.7 23 5.17 5.60 4,040 2, 635 72.1 Lodgepole pine (shipment 8B); 10 ACV eragOccs ses sere ae ee 60.6 43 5.78 6.45 , 768 2, 762 86. Maxam tin )0 os eee Se ee 89.5 52 6.00 6. 75 , 180 3, 555 126. Minimum. o22252 2 ee 2 SR 40.1 31 5. 25 6. 00 Py) 2, 090 55. Alpine fir; 9 tests: Average SBR SE a ee eee oe 99. 21 . 65 5.72 , 139 2, 450 79. Maxciauanst 25s sae Bee 147. 36 -63 6.50 ; 260 2,910 108. MINIM ee ae eee Me 57. 8 13 5.38 3 945 1, 782 7 Engelmann spruce; 11 tests
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Rocky Mountain Mine Timbers. 7
TaBLe 4.—Summary of bending tests on round beams, 16 feet long (span, 15 feet; third- point loading).
Green (Water Soaked).
F Diameter. Fiber Stiffness} Work Species, size, number of yroicture ese Modulus stress at factor to maxi- tests. inch. rupture. peut eae Top. Butt. imit. Td load. Lodgepole pine, cut “from live timber: Lbs. per Lbs. per Inch lbs. 8-inch butt, 10 tests— Per cent. Inches.| Inches.| sq. in. sq. in. per cu. in, JAN OL ARO Seer eee Uae 32 6.77 8. 20 5, 348 3, 120 10. 99 4.7 Maximum 99. 4 37 M32 8.75 6, 210 4, 200 13. 42 6.6 Minimum 62.1 28 6. 29 7.76 4, 860 2, 425 9. 26 2.6 10-inch butt, 10 tests— SAWONALCS Ss wee cee 90. 2 27 8. 26 9.97 5, 233 3, 008 10. 32 5.5 Maximum 118. 2 32 9.23 10.74 6, 230 3,905 11. 73 7.8 Minimum 73.4 21 7. 24 9.39 4,510 2,038 7.48 3.2 12-inch butt, 10 tests— WASWeravetec pce ae 4.0 91.8 23 9.82 11.62 5, 095 2, 987 10. 23 B04 Maximum. 99.6 24; 10.82; 12.41 6, 270 3, 780 13.70 7.0 MinNIMUM so ssceces 78.3 18 9.23 10.98 4, 230 2, 298 8.16 2.0 Lodgepole pine, cut from timber after standing dead for 30 years: 8-inch butt, 5 tests— PA Werage ate es 55. 38. 1 44 7.00 8. 50 5, 448 2, 905 10. 38 5.3 Maximum 45. 2 52 7.08 9.06 6, 580 3, 690 13. 25 7.6 Minimum 35.0 34 6. 92 7. 80 3,570 2, 210 8. 00 2.3 10-inch butt, 5 tests— PAW OCRASOS Sat Ane. Yao 3 40.1 40 8.21 10.24 4,940 2, 950 8. 84 3.4 Maximum 47.7 48 9.23 11.14 6, 500 4,180 10. 97 5.4 Minimum 29.8 35 7.56 9.71 3, 870 1,592 7.09 1.6 12-inch butt, 5 tests— IAN CTALC Sash eS 37.2 28 10.00 12.47 4, 430 2,320 7.71 4.3 Maximum. 41.7 34] 10.98 12.97 5, 680 2, 960 9.71 8.2 Minimum 2s 2555: 27.8 24 9.31 11.77 3, 820 1, 828 5.18 2.0 AIR SEASONED.
Lodgepole pine, cut from : live timber: 8-inch butt, 5 tests— JAVETALC soo. 2 16.8 32 6. 99 8. 04 7, 748 5,018 14.05 3.8 Maximum 19.9 34 7. 64 8.36 9,310 5, 290 16. 80 4.9 Minimum... .../ 15.2 29 6.37 7. 64 7, 160 4, 640 12. 43 ye 10-inch butt, 5 tests— Veracca fewe. ileal 25 8.09 9.77 6, 948 4,816 13. 33 Sal Maximum. 18.3 27 8.59 10.03 9, 060 5, 940 18.75 4.0 a sei ree neers 14.6 23 7.08 9. 55 4, 480 3, 190 10. 31 1.5 12-inch butt, sts— IAW ET ASO. as 3 tT 19.3 22 rise UL. 5 5, 409 3, 741 9.57 2.3 Maximum. 21.8 23 9.95 11.81 6, 350 4,340 11. 62 3.0 Minimum 17.7 21 9.55 11.14 3, 745 2, 875 6. 85 12 Lodgepole pine, cut from timber after standing dead for 30 years: 8-inch butt, 9 tests— ANCTAREC Siac e ec) 13.7 40 6. 98 8.39 5, 625 4,649 10. 92 2.1 Maximum 14.6 51 7. 64 8.91 7,780 6, 720 12.51 5.6 inimum 11.5 34 6. 45 7.48 3, 843 3,195 9. 58 8 10-inch butt, 10 tests— Average: 30522 5- Sree 12.9 34 8.27 10.11 5, 166 4, 489 10. 54 2.3 Maximum 14.4 42 8.91 10. 66 8,970 6, 400 13. 53 4.2 ANIM S oi5sa 55 - 12.1 24 7. 64 9.31 2, 690 2, 585 8.06 5 12-inch butt, 11 tests— Average 225.5 545053 13.8 31 9.16 12.15 4,720 3, 925 9. 84 7s Maximum 16.6 37 11.14} 12.49 7,310 5, 960 12. 29 3.8 Minimum 12.0 24 9.07 11.46 2,060 1,343 8.12 .4
The average results do not show a consistent difference in the relative strength of the various species tested. Figures 1 and 2 show that, with the exception of the green props and caps of Douglas fir and the dry props of lodgepole pine (Shipment B), there is not a very large difference in the strength of the various shipments. It
8 Bulletin 77, U. S. Department Of Agriculture.
is apparent from the various positions occupied by the different shipments of lodgepole pine and western yellow pine that species is not in itself a reliable guide to strength in the selection of material of this form and size. With clear material, consistent differences would probably be found between some of the species, but in the props especially the degree of straightness of the piece and the pres- ence of knots seem of greater effect than the species.
Beams.
The results of the tests on the three sizes of 16-foot round beams of lodgepole pine are shown graphically im figures 3 and 4. With the exception of the work to maximum load, all the strength functions decrease in value with increase in the diameter of the beam. The amount of this variation differs in the different kinds of material, being least in the green, greatest in the air-dried, and mtermediate in the dead timber. The reason for the decrease in the unit strength of the larger beams is not apparent. It is not due to visible defects, such as cause a decrease in the unit stress in large stringers when compared with small clear pieces cut from them, since the defects in the 8 and 12 inch beams did not differ in kind or in appearance. - The fact that stiffness decreases in the same manner as strength corroborates this statement, since such defects as knots and checks do not generally affect stiffness up to the elastic limit. The differ- ence may, however, be due, at least in part, to rate of growth, which increases in all cases with increase in diameter. The smaller beams were apparently cut from the suppressed growth of a fairly even- aged stand. The unit weight of the beams does not vary consist- ently with the strength. The dry weight per cubic foot of the air- dried beams is lowest in the 12-inch size, but for the dead beams the weight is highest in this size.
The relative values of the dead, green, and acaned timbers are also indicated in figures 3 and 4. Im strength the dead material falls between that of the air-dried and green, being close to the air- dried at the elastic limit and close to the green at the maximum load. The air-dried material is the stiffest, the green and dead having practically equal values for this factor. The closeness of the values for green and dead water-soaked material and a comparison of their curves with those of the dry timbers show very clearly the effect of moisture in reducing the stiffness and strength at the elastic limit. In work to maximum load, which is an indication of toughness, the order of the curves is reversed, the green and water-soaked beams having values about twice as great as the dry material. The posi- tion of the dead water-soaked beams, especially, brings out the fact that the greater brittleness of the dead or air-dried material is due to dryness and not to a deterioration of the wood. Drying the beams
Rocky Mountain Mine Timbers.
Hirata
Pounds Per Square Inch
a Uc eae ae Es Peccrc
Pounds Per Square Inch
Stiffness Factor
EEE ae, ee
Inch-Pounds Per Cubic Inch
DIAMETER fe BUTT= ree
Fig. 3.—Relation of unit strength of 16-foot round beams to diameter and condition. 29206°—14——_2
10 Bulletin 77, U. S. Department Of Agriculture.
increased the strength and stiffness of the wood but decreased its toughness.
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sceaual aaa Bie WORK TO MAXIMUM LOAD
fala San aap or aaaaaiael
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Fic. 4.—Relation of unit strength of 16-foot round beams to condition; based on average TEES of the three sizes tested.
In comparing fire-killed and green material, the pads of both, in regard to ordinary defects, should be taken mto consideration. The
Rocky Mountain Mine Timbers. 11
dead material tested was cut from an area supposedly burned over in 1880. In general, the surface was covered with a network of shallow worm marks (made when the bark was on and probably of no influence on the soundness). The beams, even the larger ones, were very rough and knotty, and were of poorer grade in respect to condition of knots than those cut green. The cross sections in gen- eral were sound, though here and there along the length were places beginning to form punky pockets at the surface. The fact that this material under test gave values up to the elastic limit nearly equal to those of the air-dried beams is of considerable interest, as it indi- cates that it is in excellent condition for the uses to which round material is ordinarily put.
CONCLUSIONS. The tests indicate that:
1. An air-dried mine prop is superior to a green one as follows: Strength at elastic limit 2.3 times as great. - Strength at maximum load 2.3 times as great. Stiffness 1.9 times as great. An air-dried mine cap is superior to a green one as follows: Strength at elastic limit 2.2 times as great. Strength at maximum load 1.6 times as great. Stiffness 1.4 times as great.
2. With the exception of Douglas fir, there seems to be as much variation in the strength of one species procured in different places as among the different species themselves. This is probably the result of defects such as checks, knots, and bends, which, in this size of material (5 to 6 inch diameter round caps and props), apparently overbalance the differences in the actual strength of the clear wood.
3. The unit strength and stiffness of 16-foot round beams decrease with an increase in size. The smaller beams tested, however, represented a slower growth material and were probably suppressed trees.
4. Beams cut from timber standing dead for about 30 years showed a strength in- termediate between green and air-dried material cut from live timber. The tests tend to corroborate the opinion that timber cut from dead trees can be graded on the same basis as other material; that is, the quality of the wood has not changed, from the fact that it has seasoned on the stump, and deterioration, if preseat, will be indicated by signs of decay. Checking in material to be used in the round form can hardly be considered as a defect, as it occurs in all air-dried round material.
Consumption And Durability.
Consumption Of Mine Timbers In Colorado.
The statistics here presented were collected to show the consump- tion of timber by the mining industry of Colorado? in 1911. They were obtained by sending a card to the mine operators of the State, requesting them to furnish the amounts, costs, and species of tim-
1 Colorado was chosen partly because of its importance as a mining State; partly because for the year 1911 an estimate of the entife production of wood products, including lumber, poles, crossties, round mine
timbers, and fuel was also available for direct comparison, and partly because the State is near the center of distribution of the species of mine timbers tested.
12 Bulletin 77, U. S. Department Of Agriculture.
ber used in the mines, and information concerning the life of the timber and the extent to which methods to prevent decay had been employed. A small part of the material included may have been used in structures above ground.
Reports were requested from 823 operators, 110 of whom were coal-mine and 713 metal-mine operators. Out of 352 replies, 179 (15 coal-mine and 164 metal-mine operators) reported that no timber was used during 1911, while 173 operators reported the use of timber on which the following statistics are based.
In addition to the material reported by the tables, about 1,745 cords (or 872,500 b. m.) were used for fuel.
Nearly all the timber used came from within the State. About 800,000 board feet was reported as coming from outside, mostly Douglas fir from Oregon, with a small amount of pine from New Mexico.
The timbers for use in the coal mines ranged in size from about 5 to 7 inches in diameter and from 7 to 18 feet in length. In the metal mines 8 to 10 inch diameters were the principal sizes, though timbers varying from 6 to 20 inches were reported. Lagging was usually 3 to 4 inches at the small end, and mine ties were 4 by 4 or 4 by 5 inches in section and from 36 inches in length in the metal mines to 54 inches in the coal mines.
TABLE 5.—Amounts and values of mine timbers used in Colorado in 1905, based on reports of mine operators.
Total amounts. Total values. Cost per M b. m. Mines reporting. ber of j eS: aaa neue Round. Sawed. Round. Sawed. ee See eee ee ies Coaliminestet see essere eee 69 7, 893 457 $153,152 $15, 428 $19. 40 $33.76 Metaliminesse panei eens. ace 418} 18,152 13,061 284,861 251,798 15. 69 19. 28 aS ——ee Se———eeeoyyyNT—-TqFT€q}Reoy iM rerepate masse! kes eee Se aot 39,563 M b.m.. $705,239 satin sce cee eines :
TABLE 6.—Amounts and values of mine timbers used in Colorado in 1911, based on reports of mine operators.
Total amounts. Total values. Cost per M b. m.
Mines reporting. ber of
eae quad coy eg Round. Sawed. Round. Sawed.
Goal mines. £255. 6h Fk oe 77| 10,859] 1,000 $307,372 $20,368/ $28.20] $20.37
Total (all mines) 264 17,460 7,406 446,402 161,553 25.50 21.80 ell
A'gprogate 22022. L357. eee Se 24,866 M b.m. $607,955 cr. eS RES eeeewe
The amounts were reported in linear feet, in board feet (log scale), in cubic feet, and in cords. To reduce these various units to the
Rocky Mountain Mine Timbers. 13
same basis 6 board feet were considered equivalent to 1 cubic foot of round timber and 500 board feet to a cord.
Table 5 is compiled from Forest Service Circular 49 for purposes of comparison. Table 6 gives similar data obtained for 1911. The two tables are not directly comparable, however, since the propor- tion of timber used by the mines reporting, to the whole consumption in the State, is not definitely known in either case.
Production Of Mine Timbers In Colorado.
A study of timber products was made in Colorado for the year 1911, and this furnishes some basis for an estimate of the probable total consumption of timber by the mines, including both round and sawed forms. The total production, including lumber, crossties, mine timbers, poles, fuel, and farm timbers, on the basis of the re- ports of the national forest supervisors, for both Government and private lands, was 222,808,000 board feet. The total production of round mine timbers was 36,274,000 board feet. The consumption reported, as shown in Table 6, was 17,460,000 feet of round material and 7,406,000 feet of sawed lumber. If the figure for production may be assumed as approximately correct for the actual total con- sumption and the proportion between the amounts of sawed and round forms reported holds for the total consumption, the total sawed timber used in the mines would be 15,370,000 feet and the total timber, round and sawed, would be 51,644,000 feet. This rep- resents close to $1,250,000 in total value and 23 per cent of all the timber produced in the State.
Production By Species.
The relative amounts of the different species used could not be obtained from the reports submitted by the mine operators. Based upon production, however, a close estimate is given in Table 7. The local names for certain species are different from those adopted by the Forest Service, and in order to make clear what woods are referred to, the scientific name, the common name used by the Forest Service, and the name used locally in Colorado are given below:
Scientific name. Common name used by. Common name used locally. Forest Service. Pinus contorta. Lodgepole pine. White pine. Pinus ponderosa Western yellow pine. Black jack and yellow ine. Pinus flexilis. Limber pine. ies Pinus aristata. Bristle-cone pine. Fox-tail pine. Pseudotsuga taxifolia. Douglas fir. Red spruce. Picea engelmanni. Engelmann spruce. White spruce. Picea parryana. Blue spruce. Water spruce. Abies lasiocarpa. Alpine fir. Balsam. Abies concolor. White fir. Black balsam.
Populus tremuloides. Aspen. Quaking-asp.
14 Bulletin 77, U. S. Department Of Agriculture.
TABLE 7.—Amounts by species of round mine timbers produced in Colorado in 1911.
Percent- Species. Amount. age of total. Board feet. IMMA PE POLE MING Fey LEV Ae PES ee STE Te SED EER LE RE Rook ees 23, 421, 000 65 Mike ClINANNSPRUCCE ats eee het cise ea co nee ee EO EE Sea ee ee 8, 242, 000 23 OUT AS MT ae asi hapa re eee Od cea ee 1d SORE Seana Sa Sane eae 2, 244, 000 6 iWiestermsy ellowspine®. © ace fuss See tian Ree 2 eyaisis, See ee MERC ene eee nee eee 1,354, 000 4 WIM eT Pine Sats es jae eek os oot are Pine sie S setae aan eee fa so oes SS 431, 000 1 IBTISEIE-CONE PINE 22 2. SS oe a tea ates Ber ein Ee Se eae See Se 183, 000 INST SS 5 SSRs ORAS OBESE OBST EEE RC Ene EE Booe Sorta oe ae aneurin se aducsaeseKol Seanue 149, 000 JA DTN Se GAR cae Aas SEC Ee SES SRE ene SACRE enna Hemmer Gane? NUE A Wee Se dae 109, 000 1 IEICIS PRU COs sere ee cee oes ee cae nea as rete rete 8) re Orin ee eee Sn ee 75, 000 \NVADMT RESET OS Ss res eae a ee eo Nee eri eal uO Ang RN SION, eae ce AeA Sa ea tie EM gE Sy Sele: 65, 000 (OES FS Ses eS SES OS es eS a ren I Se Ree SNE Se Seo Sars aerial 1,900 ING Ace OAS Sea ah MO lh Ene aerial ete Pei A SIL he 36, 274, 000 100
TABLE 8.— Unit costs for various diameters.
: : Cost per inch of pate Cost Del piece 16 Cost perlinearfoot.| diameter 16 feet : g- long. Inches. 3 $0. 35 $0. 022 $0. 117 4 - 40 to $0.50 . 025 to $0.031 . 100 to $0. 125 6 -45to .65 .028to .041 .075 to .108 8 -60to 1.25 .038 to .078 -075 to .156 10 1.15 to 1.60 .072to .100 .115to .160 12 1.50 to 2.15 .094 to .135 .125to .180 14 2.00 to 2.25 125 to~ 2141 - .143to .161 16 2. 50 . 156 156
Table 7 shows that lodgepole pine is the main source of supply for round mine timbers, and, together with Engelmann spruce, makes up 88 per cent of all the props cut. Douglas fir, although a very desir- able wood, formed only 6 per cent of the total.
Costs For Different Sizes.
Table 8, giving costs for props of various diameters, was compiled from such data submitted by the operators as were definite in regard to the size of the material. Several methods of purchasing round material were reported—cost per piece for a given length and diam- eter, cost per linear foot for a given diameter, and cost per inch of diameter at the small end for a given length. A large majority reported the cost per linear foot.
Life Of Timbers.
There was a large variation in the reported life of timbers in the different mines, especially in the metal mines. The timbers in the coal mines had an average life of only about one-half that found in the metal mines, but their size was also only about one-half as great. Tables 9 and 10 give the average values obtained from statements of the operators.
Rocky Mountain Mine Timbers. 15
TaBLE 9.—Reported life of untreated round mine timbers in coal mines (mostly 5 to 7 inches diameter).
Engel- ; Doug: pine. mann Alpine r spruce. ;
Conditions in mine.
Years.| Years.| Years.| Years.| Years.
IMO Shc Gah GAet aS 6S onda eoenbes gous 6 papad ease os oeoerouauue™ 5 4 4
ROOTRV GIGI AION i ers es Seve asa ye Ue rl oro ooo earsreere 2 1 1 ales rier 1 Goodiventilatione tt tit. t-s See a SEeER ce SER Ee 10 8 CC IPS Hea 6 ECO NOM A etes Gaenee een So dimlelc cates Se ats ssa Saltese te 25 LEGS I ene I Ae ae
1 Includes lodgepole pine and western yellow pine.
TABLE 10.—Reported life of untreated round mine timbers.in metal mines (mostly 8 to 10 inches diameter).
Fe é : Douglas Western Lodgepole Engelmann
Conditions in mine. fir. yellow pine. pine. spruce.
Years. Years. Years. Years. Average Sy SAS eR il I Ee a ae 9 8 WernyapooLrsvientilation sess 2st seeee 5.25 toe ue 2to 5 lto 3 1 to 2 Itoe2 Constanthyawiet ame eee eee eco eset sare yee 20 to 40 GO F255) Saye aeeeer 15 to 20
The conditions under which the estimates were made vary so much that the relative life of the different species 1s probably not reliable. For example, several operators reported that under the same condi- tions Douglas fir outlasts lodgepole pine or spruce two to three times; yet the average values show comparatively little variation among the species.
The factors that cause variation in the life of the timbers are prin- cipally ventilation, moisture, acid mine water, and the condition of the timbers when placed. The influence of fresh and compara- tively dry air was clearly indicated in several mines which reported a life fully four times as long for the timbers in the intake shaft as for those in the return shaft (8 and 2 years, respectively). Several operators reported that they had increased the Jife of their timbers from two to three times by peeling and seasoning them before place- ment. Certain mines reported that their timbers were sound after standing from 25 to 35 years under conditions where they were nearly always wet, and in one or two cases the water was stated to contain “sulphuric acd” or ‘‘copper and arsenic,’’ which probably acted as an antiseptic. Both constantly wet and constantly dry conditions appear, from the replies, to be favorable to a long life, while damp- ness, due to stagnant air, or alternating dryness and wetness, appears to furnish the best conditions for the growth of wood-destroying fungi.
Preservative Treatment.
Preservative treatment to prevent decay was not regularly prac- ticed at any of the mines reporting. Sixteen operators referred to some use of preservatives, though none had had a long enough expe- rience to furnish data on the increased life from such treatment. The methods spoken of were dipping in creosote or crude oil, and brush
16 Bulletin 77, U. 8. Department Of Agriculture.
treatments with creosote, carbolineum, or crude oil. One operator referred to the disagreeable effect on the miners of the odor from the creosote in the mine.
There was great variation in the replies to the question regarding the proportion of timber used for replacements made necessary by decay. Replies from 30 coal mines averaged 11 per cent (14 reporting 0 per cent and none 100 per cent), and from 112 metal mines aver- aged 21 per cent (44 reporting 0 per cent and 11 reporting 100 per cent). It is apparent that the economy of preservative treatment is a local problem with each mine.
In order to decide whether it would be economical in any given case to apply treatment only a few factors concerning the present costs and life of the timbers are essential. The proper method! of treat- ment would depend upon species of wood, capacity of apparatus, and local conditions, but the preliminary steps could be taken on the basis of the following data:
1. The amount and cost of material that goes annually toward replacing decayed timbers.
2. The cost, in place, of the lice used.
3. The average life of the timber.
The first of these factors will readily show whether the amount concerned is large enough to warrant further consideration of pre- servative treatment. In certain coal mines, where but few timbers are necessary in the permanent entries and where the majority of timbers are used in temporary positions, a brush treatment would probably be all that is warranted, unless impregnated material could be procured in the market. On the other hand, where a large amount of material is used to replace decayed timbers the installation of a small treating plant might be seriously considered.
From the cost in place and the average life of the timbers there can be calculated an annual charge, a measure of the relative economy, with which any other combination of cost and life (such as that resulting from a preservative treatment of the timber or perhaps from the use of some other kind of material) can be compared. In figure 5 is presented a series of curves, each for a definite initial cost of a timber or set of timbers, which show the relation between length of life and annual charge when compound interest on the investment is considered and maintenance is assumed for an indefinite time.”
1 Forest Service Bulletin 107, The Preservation of Mine Timbers, by E. W. Peters, treats of various methods of preserving mine timbers from decay. :
2 The annual charges are figured on this basis so that a fair comparison can be made between different methods involving various combinations of costs and length ofservice. Ifa material were placed that would last forever its annual charge would be simply the interest on the cost in place. If the material must be replaced every so often, the annual charge represents the interest on a sum of money which, if placed at compound interest, would pay for the initial cost in place and all future replacements and would be itself used up at the end of the period of maintenance under consideration. If this period be of an indefinite length (forever), the annual charge is the interest on a sum of money sufficient to pay the present cost of
installation and, by the accumulation of compound interest on the balance, take care of future replace- ments at the assumed intervals of time. .
Annual Charge — Dollars
ut
CEES eae eee ee ae
Rocky Mountain Mine Timbers. 17
Sema cena ee ee ee EE ee
APS See ANNUAL CKARGE R- US eae aaa a ist eee alesis [bal Pt TTT TT TT TT TT TY meamrriac cost in piace-pomnars SS ERE a of M=LIFE OF TIMBER—YEARS Meee eee eee ese ee ci a ee Seeded! tala eh
ial H
reer CE A REFEREES Eo EEE pepo Sivas Sea ptt tf
(el et ES 25 dS SS eH Bb Teed Ta eS eae a OL ete Ws hee [eo] JOE ane aae ee eS NU (BSCS, (a ala a SS ss Le Li Haat ea fle 21 Pr i (ea ) Fy 01H ln sO EO eann liane epee elie alee less fee [liseebebo Robs delodl pd HALA A bal es
a Re ea ea ai
A Meena eee ee mG ON INe LIS a eee fey OSE DNS ES Se ae eee aS ENS aN ONIeSR SLLS 2805 Se Sneees ; TS Sinn ee a ES a ee hy
LIFE Ind YEARS
Fig. 5.—Relation between life of timbers and annual charge.
29206°—14——-3
18 Bulletin 77, U. S. Department Of Agriculture.
The curves will show how much additional initial cost is warranted when a given increase in life due to the treatment under consideration is assumed and the initial cost and life for the existing conditions are known. The diagram also illustrates graphically, by the steepness of the curves, the great economy in prolonging the life of timbers that ordinarily last but a few years.
To illustrate the use of the curves, assume that an operator wants to find out approximately what saving he would effect by carrying out some proposed scheme to lengthen the life of his timbers in cer- tain permanent openings. Assume that each timber set costs $6, including the expense of framing and setting. If its life is five years, its annual charge as shown by the curves is approximately $1.40, Let us next assume that the proposed treatment will double the life; that is, give the timbers a service of 10 years. A further inspection of the curves at the line of 10 years’ life shows that the same annual charge of $1.40 results from an initial cost of $10.50. In other words, the economy of a timber that costs $6 in place and lasts five years is the same as one that costs $10.50 and lasts 10 years; and, therefore, the proposed treatment would pay if the final cost of the treated timber was anything less than $10.50. If we assume the cost of the treat- ment to be $1.50 for each timber (making the total cost in place $7.50) the annual charge would be about $1. The cost of using treated tim- bers would increase the total cost of timbering each year until the period of the natural (untreated) life of the timbers (five years in this example) had been passed; after that time, however, there would be a period of very low total costs until it was necessary to replace the treated material. The economy shown in an annual charge of $1 in comparison with $1.40 represents the average conditions due to a continuous maintenance. It means, expressed in another way, that the investment required to maintain the untreated timber perma- nently would be $28, and that the investment for the maintenance of the treated timber would be $20, under the conditions given in this example.
Appendix. Methods.
Testing.
The 6-foot props were tested in compression parallel to the grain at a speed of 0.119 inch per minute. bearing block was used between the prop and the base of the machine. The compression of the prop, as indicated by the movement of the head of the testing machine, was read to thousandths of an inch by means of an Olsen deflectometer. Figure 6 shows a prop in the testing machine after failure.
The 8-foot caps were tected on a 7-foot span with third-point load- ing. The tests were made on a 200,000-pound Riehle testing machine at a speed of 0.231 inch per minute. The ends were supported by curved cast-iron bearing blocks and the load applied at two points (one-third the length of the span from either end) through curved wooden blocks. Deflections were read at the center of the beam to hundredths of an inch by observing on a taut string the movement of a polished metal scale attached to the timber. The method of loading is shown in figure 7, all parts of the testing machine being omitted except the weighing platform.
The 16-foot lodgepole pine beams were tested on a 15-foot span with third-point loading. The arrangement was similar to that
used for the caps. MOISTURE DETERMINATIONS.
A 1-inch section was cut from near the point of failure of each piece tested. This was immediately weighed and later dried to con- stant weight at the temperature of boilmg water. The loss in weight divided by the dry weight, expressed in per cent, is the moisture content of the piece.
General Observations.
The length, weight, and diameters of the timbers were obtained just before testing. The rings per inch and the proportion of sapwood and of summerwood were obtained from a section cut near the point of failure. The values for the amount of summerwood are approxt- mate, as the summerwood bands were not distinctly marked in many of the pieces.
Computations.
The load and deflection at the elastic limit were obtained from the
load-deflection curve, and at maximum load by direct observation.
20 Bulletin 77, U. S. Department Of Agriculture.
The fiber stress at the elastic limit and the modulus of rupture were computed for the diameter and moment of inertia obtaining under the a) loading point, the section being regarded as a true circle. The stiffness
factor was obtained
from the moment of in- ertia (I) and the deflec- tion (d) at the center of the beam. These values for stiffness are compar- able for pieces of the Same span only. ‘The true modulus of elasticity, which is difficult to ob- tain accurately for a beam with a varying moment of inertia, depends upon Aan in the cube of the span. s ee Hh A This relation is not con- is Hi sidered in the ‘‘stiffness
—S
Cua Aat
factor”’ used, “, and this
causes the values for the 7-foot span to be approxi- mately ten times as large as for the 15-foot span. The work to maximum load was calculated from the area under the load- deflection curve, and is given in terms of unit i volume. In the calcula- ~—s tions involving the unit Wes MM 2 stresses of the props, the We top area of the prop was used.
The volume of the test pieces was calculated by multiplying the average of the areas of the top, the butt, and the mean proportional between them, by the length. The weight per cubic foot was obtained from this estimated vol- ume, and is therefore given as “approximate.”
Ny : HI Cal me
wn
Fic. 6.—Method used in testing mine props in compression.
fa )
Rocky Mountain Mine Timbers.
TaBLE 11.—Data on individual crushing tests of green round mine props (nominal. size, 5-inch top by 6 feet long).
Remarks. ,
Grain slightly. sp iral.;
Slightly crooke
Grain slightly spiral.
5 knots in failure plane.
Unusually knotty.
Grain spiral.
Do.
Slightly crooked. — Do. Grain spiral.
Do.
Slightly decayed. Grain spiral.
Grain slightly spiral. Do.
Crooked. Grain spiral. Crooked.
Grain slightly spiral. Crooked.
Grain spiral. Do.
Do.
Do. Do.
Es : 5 E , Diameter. 3g Sx a 5 ae laid Ba jee Peo. qh" ws 7. o . me ° — v 2 CMS la A oO oo 3 & QB a Q oO : eI a, 6 ae S 2 Le) Cae lenetee Silnaln]) & (Saha kd) O 1,000 Lbs. Lbs. lbs. Per |Lbs. per Per| Per per per per cent. cu.ft. cent.| cent. In. In. sq. in.| sq. in.| sq. in. ment A). Dit SO 2225825 25.1220 20 4.46 5.16 11,515 1,280 459 4/ 66.9] 25.33 38) 14] 42] 5.60] 6.30 2,200 1,946] 718
Bulletin 77, U. §. Department Of Agriculture.
TaBLe 11.—Data on individual crushing tests of green round mine props (nominal size, 5-inch top by 6 feet long)—Continued.
Species.
Bristle-cone pine.
AW EO Hees
Western yel- low pine (shipment
+i.
Av’ge.
Western yel- low pine (shipment
B.)
Rings per inch,
Summerwood.
maximum
Crushing strength at
Bse
&
Qo ¢
OOnN ee
PH fe bet bed bet bt bt fet fet WRN Or
Or? Ov Or if OD ay
g
Crushing strength at elastic limit.
yo ° on Z Se @ - Hes co o -——S a] 3 (838 S ° a2 Per Lbs. per cent. cu.ft 4 106.1] 26.17 6 56.1) 23.68 9 1101.0 25.72 85.9 27.68 91.8! 22.67 DAP97- 8.41) 2os0o 92.0] 23.55 7 101.2 22.71 a6 eg Ss 96.1 23.18 81.1] 25.68 90.5 23.22 83.0} 24.80 {LES (een es 54.8 25.92 63.5 21.58 78.8 24.62 105.5 24.7 76.6 26.20 72.8 26.28 soe 82.0 24.78
Diameter. a 2 [a= In. In. 4.25 5.13 4.65 5.50 4.80 5.50 5.33 6.40 4.52 4.91 3.98 4.77 4.46 5.17 5.17 6.05 4.38 5.16 4.30 5.17 4.58 5.38 4.25 5.25 4.25 5.00 4.35 5.10 4.70 5.40 4.65 5.60 4.30 5.13 4.78 5.16 4.38 5.41 4.14 4.94 4.62 5.01 4.44 5.20 5.25 6.15 5.01 5.73 5.65 6.13 5.33 6.17 5.49 6.05 5.41 6.05 5.33 5.97 5.49 5.81 5.41 6.05 5.09 5.89 5.35 6.00
Modulus of elas- ticity.
Remarks.
Crooked.
Crooked and unusu- aly knotty.
oO. Grain slightly spiral.
Do.
Crooked. Do. Do.
Grain slightly spiral. Do. Unusually knotty. Grain slightly spiral. O.
Grain spiral, crooked.
Rocky Mountain Mine Timbers. 23
TABLE 12.—Data on individual crushing tests of air-seasoned round mine props (nominal size, 5-inch top by 6 feet long).
5 z Diameter. sg a & 2 £8 Oo. S ° 2. ia Smt oe Z Rae Ars B So Ob Species. S ey & 22/15 e a 8 Salas! Remarks. st) Lash eS Alcon eo male riers u S 0.28 eg Ps : nau iicele See se) CO hats) & Ae) AYan] ¢ g a, Q aay ae g se |%3 D Seelam cual (hel ee 5 S |[pes| Ss (oxi ai| met Salto a a Ef A We S) Lbs Per |Lbs.-per Per| Per per cent. cu.ft. cent.| cent.| In. Jn. sq. in. Led gepole 1) 11.5} 24.58) 51] 21] 55 4.85 5.17 3, 465 Grain spiral. ment A). 3, 11.2} 27.96; 57] 18] 383 5.17 5.57 4,190 Do. 5 11.0] 25.83] 47] 19] 385 4.77 5.25 3, 580 Do. PAS 20 alo ac 11.5] 25.40] 46] 20} 50) 4.93 5.43 3,513 Lod gepole 6 11.0] 28.14] 43 26] 42] 4.38 5 01 4,110 Do. ment B). 8 15.9] 23.42] 50] 26) 61) 5.17] 5.49 4,010 Do. 11.2] 29.52] 45} 20) 37] 4.01 5.73 4,750 Do. OSS EL Nal tesa Le Ya sea Pa len 4.46 5.33 4,260 3,875 |1,043 spruce. 2) 11.2] 28.10 25] 13 ] 5.09 5.49 2,555 Do. SUPA) F235 3501829) Sal3 eee: 3.50 4.62 3, 120 Do. 4] 138.0] 24.00} 43} 22 ) 3.98 5.25 2, 410 Crooked. eel Seip aoe o28nle- se 4.30 4.93 3, 850 Grain spiral. 6] 11.3] 23.86 31] 20] 4.62 5.33 3, 822 CoalPLOSS ahs 212785 1Guee2 a 4.85 5.49 3, 030 Douglas fir..| 1] 11.9] 31.63! 76| 25] 31 4.30 4.62 2,340 Crooked; grain spiral. usually knotty. 3] 11.6] 28.98 65 28] 39] 4.85 5.17 3, 465 Crooked; grain spiral. knotty. S254 esos abn) 42n 020s. - 3.66 4.22 2, 280 Crooked; grain spiral. OelelZe2 coasie| oon 20M ss- 3.98 4.85 2, 890 low pine 2) 11.1} 23.55) 15} 18 88 4.30 4.62 3,310 Grain spiral. Ouiel ss 4eiie23.69 We] 12) iooos. 4.14 4.85 2, 822 low pine alle Gule 24030 19 Wee ooe. 4.70 5.25 3, 690 (Grain spiral. (shipment Sa SsO8 eZ (eg25| ol 20) oe. 4.93 5.65 3, 350 B). Male tite sy G25 0780113) e19"| 222) 4.93 5.41 3, 770 Do. LOMPLOSO 23-645) 12 W475 4.62 5.33 2,270 Grain spiral, crooked.
—Eee———
Bulletin 77, U. S. Department Of Agriculture.
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Bulletin 77, U. S. Department Of Agriculture.
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Rocky Mountain Mine Timbers. 33 Manner Of Failure.
The prop failures were quite uniform. Compression wrinkles occurred usually through one or more knots and, if the prop had a slight bend in it, the wrinkles were on the concave side at the point of greatest eccentricity. If this bend were at all prominent, tension often occurred and in several instances the prop separated in two parts as in the brittle cap failure. The influence of checks on the form of failures was quite noticeable in the dry props, the shortening of the props giving the check, if spiral, the appearance of “‘ unwinding”’ asin the strands of arope. Figure 6 shows this effect to some extent.
Fic. 7.-Method used in testing mine caps in bending.
Caps.
The failures of the green caps were quite uniform in character among the various species. Near or at the maximum load, com- pression took place on the upper surface between the loading points. The load fell off slowly, and if continued, failure by tension ultimately took place. The green Alpine fir caps, however, had a larger propor- tion of tension than compression failures, and the Douglas fir had approximately the same number of each.
The dry caps, as far as could be detected by the eye, generally failed in tension near the center. Occasionally compression wrinkles oc- curred, but the failures were more often sudden, and some indicated brittle material. There was no material difference in the failure of the different species. In the dry material the tension splinters often ended at a check, but it was not apparent that the type of failure or
34 Bulletin 77, U. S. Department Of Agriculture.
strength of the specimen was definitely influenced by the seasoning aa even when more or less spiral.
Beams.
The beam failures were similar to those occurring in the caps. The water-soaked material failed almost entirely in compression on the upper surface, the failure wrinkles becoming visible shortly before the maximum load was reached. Some of the green beams had a- very large deflection, and the stress-strain curves were typically somewhat flat topped. The dry beams failed in tension, sometimes accompanied by failure in compression.
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