Strength of Woods

The crushing strength of green wood of the principal species is approximately as indicated in Table 4.

Tensile Strength.

Tensile strength is the opposite of crushing strength, or the force required. to pull a substance apart. The tensile strength of wood parallel to the grain is from two to four times as great as the corresponding crushing strength, and considerably greater for hardwoods than for softwoods. When placed under compression, the of wood tend to buckle or bend, and thus give way; but they offer great resistance to a force which tends to pull them apart.

Although the tensile strength of wood is many times referred to, in popular statements, as being a most important property, it is really not so necessary to determine, for most uses, as the resistance to bending and crushing. For all ordinary purposes, the tensile strength of wood is greater than stress of this sort to which it will be subjected, and hence no detailed discussion of the topic is necessary.

Table 5 Shearing Strength of Various Woods Pounds per Square Inch Softwoods Fir, Amabilis 578 Pine, Table Mountain. 712 Spruce, Englemann 592 Spruce, Eastern 721 Fir, Alpine 614 Fir, White 732 Cedar, Northern White 616 Fir, Grand ..... 735 Cedar, Incense 638 Pine, Norway 776 Pine, White 644 Cypress 818 Pine, Western Yellow. 684 Douglas Fir ' 856 Cedar, Western Red... 698 Tamarack 863 Pine, Sugar 708 Hemlock, Eastern .... 876 Pine, Shortleaf 708 Pine, Longleaf 1,006 Pine, Lodgepole 712 Average Shearing Strength 730 Hardwoods Willow 562 Ash, Pumpkin 1,214 Basswood 607 Birch, Sweet 1,220 Buckeye, Yellow 662 Oak, Yellow 1,237 Cherry, Red 678 Hickory, Bitternut.... 1,237 Butternut 756 Oak, White 1,251 Aspen 813 Elm, Rock 1,270 Ash, Black 860 Hickory, Mockernut... 1,276 Elm, White 873 Oak, Swamp White . . . 1,296 Cucumber 991 Oak, Post 1,299 Sycamore 1,001 Ash, Green 1,318 Tupelo 1,031 Hickory, Pignut 1,348 Hickory, Nutmeg 1,032 Oak, Bur 1,354 Maple, Silver 1,053 Maple, Sugar 1,380 Hackberry 1,093 Ash, White 1,380 Birch, Yellow 1,115 Hickory, Shagbark ... 1,298 Witch Hazel 1,118 Oak, Tanbark 1,414 Cherry, Black 1,127 Hickory, Water 1,440 Oak, Red 1,146 Dogwood 1,516 Elm, Slippery 1,148 Ash, Blue 1,544 Maple, Red 1,157 Laurel, Mountain 1,669 Hickory, Big Shellbark 1,187 Locust, Black 1,755 Beech 1,210 Locust, Honey 1,990 Average Shearing Strength 1,180 Shearing Strength. The resistance which wood offers to a force which tends to make the fibers slip on one another, is called "shearing strength," and for many uses it is important that the shearing strength parallel to the grain be determined. This will be discussed later in the chapter on Paving Blocks. At this point it is necessary only to insert the tables which show the comparative shearing strength of the various species of wood, as determined by tests upon small pieces. The results, shown in Table 5, are given in pounds per square inch.