| TABLE XXII | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| WORKING UNIT-STRESSES FOR STRUCTURAL TIMBER[c] | ||||||||||||||
| EXPRESSED IN POUNDS PER SQUARE INCH | ||||||||||||||
| (From Manual of the American Railway Engineering Assn., 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. | ||||||||||||||
| KIND OF TIMBER | BENDING | SHEARING | COMPRESSION | Ratio of length of stringer to depth | ||||||||||
| Extreme fibre stress | Modulus of elasticity | Parallel to the grain | Longitudinal shear in beams | Perpendicular to the grain | Parallel to the grain | For columns under 15 diameters working stress | Formulæ for working stress in long columns over 15 diameters | |||||||
| Average ultimate | Working stress | Average | Average ultimate | Working stress | Average ultimate | Working stress | Elastic limit | Working stress | Average ultimate | Working stress | ||||
| 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 to be used without increasing the live load stresses for impact. | l = Length in inches. 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] | ||||||||||||||