[Illustration: FIG. 5.--Testing a buggy spoke in endwise compression, illustrating the failure by sidewise bending of a long column fixed only at the lower end. _Photo by U. S. Forest Service_]
The lateral bending of a column produces a combination of bending with compressive stress over the section, the compressive stress being maximum at the section of greatest deflection on the concave side. The convex surface is under tension, as in an ordinary beam test. (See Fig. 6.) If the same stick is braced in such a way that flexure is prevented, its supporting strength is increased enormously, since the compressive stress acts uniformly over the section, and failure is by crushing or splitting, as in small blocks. In all columns free to bend in any direction the deflection will be seen in the direction in which the column is least stiff. This sidewise bending can be overcome by making pillars and columns thicker in the middle than at the ends, and by bracing studding, props, and compression members of trusses. The strength of a column also depends to a considerable extent upon whether the ends are free to turn or are fixed.
[Illustration: FIG. 6.--Unequal distribution of stress in a long column due to lateral bending.]
|-------------------------------------------------------| | TABLE IV | |-------------------------------------------------------| | RESULTS OF COMPRESSION TESTS ACROSS THE GRAIN ON | | 51 WOODS IN GREEN CONDITION, AND COMPARISON WITH | | WHITE OAK | | (U. S. Forest Service) | |-------------------------------------------------------| | | Fibre stress | Fiber stress | | COMMON NAME | at elastic | in per cent | | OF SPECIES | limit | of white oak, | | | perpendicular | or 853 pounds | | | to grain | per sq. in. | |-----------------------+---------------+---------------| | | Lbs. per | | | | sq. inch | Per cent | | | | | | Osage orange | 2,260 | 265.0 | | Honey locust | 1,684 | 197.5 | | Black locust | 1,426 | 167.2 | | Post oak | 1,148 | 134.6 | | Pignut hickory | 1,142 | 133.9 | | Water hickory | 1,088 | 127.5 | | Shagbark hickory | 1,070 | 125.5 | | Mockernut hickory | 1,012 | 118.6 | | Big shellbark hickory | 997 | 116.9 | | Bitternut hickory | 986 | 115.7 | | Nutmeg hickory | 938 | 110.0 | | Yellow oak | 857 | 100.5 | | White oak | 853 | 100.0 | | Bur oak | 836 | 98.0 | | White ash | 828 | 97.1 | | Red oak | 778 | 91.2 | | Sugar maple | 742 | 87.0 | | Rock elm | 696 | 81.6 | | Beech | 607 | 71.2 | | Slippery elm | 599 | 70.2 | | Redwood | 578 | 67.8 | | Bald cypress | 548 | 64.3 | | Red maple | 531 | 62.3 | | Hackberry | 525 | 61.6 | | Incense cedar | 518 | 60.8 | | Hemlock | 497 | 58.3 | | Longleaf pine | 491 | 57.6 | | Tamarack | 480 | 56.3 | | Silver maple | 456 | 53.5 | | Yellow birch | 454 | 53.2 | | Tupelo | 451 | 52.9 | | Black cherry | 444 | 52.1 | | Sycamore | 433 | 50.8 | | Douglas fir | 427 | 50.1 | | Cucumber tree | 408 | 47.8 | | Shortleaf pine | 400 | 46.9 | | Red pine | 358 | 42.0 | | Sugar pine | 353 | 41.1 | | White elm | 351 | 41.2 | | Western yellow pine | 348 | 40.8 | | Lodgepole pine | 348 | 40.8 | | Red spruce | 345 | 40.5 | | White pine | 314 | 36.8 | | Engelman spruce | 290 | 34.0 | | Arborvitæ | 288 | 33.8 | | Largetooth aspen | 269 | 31.5 | | White spruce | 262 | 30.7 | | Butternut | 258 | 30.3 | | Buckeye (yellow) | 210 | 24.6 | | Basswood | 209 | 24.5 | | Black willow | 193 | 22.6 | |-------------------------------------------------------|