Strength of Woods

STRENGTH OF WOODS It is most important that the users of timber Table 1 Specific Gravity of Various Woods (Test pieces "oven-dry") Softwoods Cedar, Northern White.. .29 Fir, Amabilis 38 Cedar, Western Red .... .29 Hemlock, Eastern 38 Spruce, Englemann .... .31 Spruce, Red 38 Fir, Alpine 31 Pine, Table Mountain ... .39 Spruce, White 32 Douglas Fir .42 Redwood 35 Hemlock, Black 42 Fir, White 35 Hemlock, Western 42 Pine, Sugar 36 Pine, Norway 44 Pine, White 36 Cypress 45 Cedar, Incense 36 Larch, Western 46 Pine, Western Yellow... .37 Pine, Shortleaf 48 Pine, Lodgepole 37 Tamarack .49 Fir, Grand 38 Pine, Longleaf 53 Average Specific Gravity of Softwoods 39 Hardwoods Buckeye, Yellow .33 Hickory, Nutmeg 56 Willow, Black 33 Witch Hazel 56 Basswood 34 Maple, Hard 56 Aspen, Largetooth 35 Oak, Tanbark 56 BUtternut 36 Oak, Yellow 56 Cherry, Red .36 Oak, Red 57 Elm, White 43 Elm, Rock 58 Gum, Red 43 Oak, Bur .58 Maple, Silver 44 Birch, Sweet 59 Cucumber 44 Oak, Post 59 Sumac 45 Oak, White 60 Sycamore 45 Laurel, Mountain .62 Ash, Black 47 Hickory, Bitternut 62 Cherry, Black .47 Hickory, Water 63 Elm, Slippery 47 Hickory, Shagbark 63 Tupelo 48 Hickory, Big Shellbark.. .63 Hackberry 48 Oak, Swamp White 64 Ash, Pumpkin .49 Dogwood 64 Maple, Red 49 Hickory, Mockernut .... .65 Ash, Blue 53 Hickory, Pignut 66 Ash, Green 53 Locust, Black 66 Beech 54 Locust, Honey 70 Ash, White 55 Osage Orange 76 Birch, Yellow 55 Average Specific Gravity of Hardwoods.... .53 have some idea of the resistance which the common woods offer to cross-breakage, to crushing, and to what is called "shearing." The crossbreaking strength of a piece of timber is the force which is required to break it when it is supported at the ends and loaded between these points. The crushing strength is the resistance which a stick offers to crushing when loaded as in the case of a railroad tie. The shearing strength is the resistance offered to a force which tends to make the fibers shear or slide past one another.

Breaking or Bending Strength.

The crossbreaking strength of timber is tested in the laboratory by placing a stick on supports at each end, and loading it at a uniform rate until it breaks. Accurate notation is made of the size of the stick; length of span; the amount of deflection, or the extent to which the stick bends, under various loads; and the weight which finally breaks it. From this information, several fac

tors are determined—one, which best represents the resistance to cross-breakage, being called the "modulus of rupture" and expressed in pounds per square inch.

The cross-breaking strength of a piece of wood varies directly with the length of the stick, and inversely with the square of the thickness; thus, if a weight of 400 pounds breaks a stick 4 feet long, a weight of 200 pounds will break a stick 8 feet-long, all other factors being the same. On the other hand, if a weight of Table 2 Modulus of Rupture of Various Woods Test pieces 2 in. square, 28 in. span, of green, clear Average results Softwoods Spruce, Englemann... 4,200 Cedar, Incense 6,040 Cedar, Northern White 4,260 Fir, Grand 6,090 Fir, Alpine 4,460 Hemlock, Eastern .... 6,180 Cedar, Western Red 4,750 Douglas Fir 6,340 Pine, Western Yellow. 5,090 Pine, Norway 6,430 Pine, Lodgepole 6,150 Fir, Amabilis 6,570 Spruce, White 5,200 Redwood 7,000 Pine, Sugar 6,270 Cypress 7,110 Pine, White 6,310 Tamarack 7,170 Pine, Table Mountain. 5,700 Larch, Western 7,260 Spruce, Red 5,710 Hemlock, Western ... 7,290 Fir, White 5,970 Pine, Shortleaf 7,710 Hemlock, Black 6,030 Pine, Longleaf 8,630 Average Modulus of Rupture of Softwoods. ... 6,040 Hardwoods Willow, Black 3,340 Beech 8,160 Buckeye, Yellow 4,820 Witch Hazel 8,280 Basswood 4,860 Laurel, Mountain .... 8,440 Cherry, Red 6,040 Birch, Sweet 8,690 Butternut 6,370 Birch, Yellow 8,600 Maple, Silver 6,820 Dogwood 8,790 Sumac 6,845 Hickory, Nutmeg 9,060 Aspen, Largetooth ... 6,850 Maple, Hard 9,060 Ash, Black 6,000 Elm, Rock 9,430 Hackberry 6,210 Ash, Blue 9,650 Sycamore 6,300 Ash, White 9,853 Gum, Red 6,450 Oak, Swamp White... 9,860 Elm, White 6,960 Ash, Green 10,040 Oak, Bur 7,180 Hickory, Bitternut... .10,280 Tupelo 7,380 Hickory, Big Shellbark.10,490 Oak, Post 7,380 Oak, Tanbark 10,710 Cucumber 7,420 Hickory, Water 10,740 Ash, Pumpkin 7,600 Hickory, Shagbark ...10,870 Elm, Slippery 7,710 Hickory, Afockernut.. . 11,560 Maple, Red 7,890 Hickory, Pignut 11,850 Oak, Red 8,000 Locust, Honey 12,360 Cherry, Black 8,030 Osage Orange 13,660 Oak, Yellow 8,110 Locust, Black 13,800 Oak, White 8,160 Average Modulus of Rupture of Hardwoods...8,350 400 pounds breaks a stick 2 inches thick, it will require a weight of pounds to break a stick of the same material 4 inches thick.