Figure 11
Failures of test specimens in shear along the grain. In the block at the left the surface of failure is radial; in the one at the right, tangential.
| TABLE VII | ||
|---|---|---|
| SHEARING STRENGTH ALONG THE GRAIN OF SMALL CLEAR PIECES OF 41 WOODS IN GREEN CONDITION | ||
| (Forest Service Cir. 213) | ||
| COMMON NAME OF SPECIES | When surface of failure is radial | When surface of failure is tangential |
| Lbs. per sq. inch | Lbs. per sq. inch | |
| Hardwoods | ||
| Ash, black | 876 | 832 |
| white | 1,360 | 1,312 |
| Basswood | 560 | 617 |
| Beech | 1,154 | 1,375 |
| Birch, yellow | 1,103 | 1,188 |
| Elm, slippery | 1,197 | 1,174 |
| white | 778 | 872 |
| Hackberry | 1,095 | 1,161 |
| Hickory, big shellbark | 1,134 | 1,191 |
| bitternut | 1,134 | 1,348 |
| mockernut | 1,251 | 1,313 |
| nutmeg | 1,010 | 1,053 |
| pignut | 1,334 | 1,457 |
| shagbark | 1,230 | 1,297 |
| water | 1,390 | 1,490 |
| Locust, honey | 1,885 | 2,096 |
| Maple, red | 1,130 | 1,330 |
| sugar | 1,193 | 1,455 |
| Oak, post | 1,196 | 1,402 |
| red | 1,132 | 1,195 |
| swamp white | 1,198 | 1,394 |
| white | 1,096 | 1,292 |
| yellow | 1,162 | 1,196 |
| Sycamore | 900 | 1,102 |
| Tupelo | 978 | 1,084 |
| Conifers | ||
| Arborvitæ | 617 | 614 |
| Cedar, incense | 613 | 662 |
| Cypress, bald | 836 | 800 |
| Fir, alpine | 573 | 654 |
| amabilis | 517 | 639 |
| Douglas | 853 | 858 |
| white | 742 | 723 |
| Hemlock | 790 | 813 |
| Pine, lodgepole | 672 | 747 |
| longleaf | 1,060 | 953 |
| red | 812 | 741 |
| sugar | 702 | 714 |
| western yellow | 686 | 706 |
| white | 649 | 639 |
| Spruce, Engelmann | 607 | 624 |
| Tamarack | 883 | 843 |
Both shearing stresses may act at the same time. Thus the weight carried by a beam tends to shear it off at right angles to the axis; this stress is equal to the resultant force acting perpendicularly at any point, and in a beam uniformly loaded and supported at either end is maximum at the points of support and zero at the centre. In addition there is a shearing force tending to move the fibres of the beam past each other in a longitudinal direction. ([See Fig. 12].) This longitudinal shear is maximum at the neutral plane and decreases toward the upper and lower surfaces.
Figure 12
Horizontal shear in a beam.