6.8: Bearing Stresses

6.8 Bearing Stresses

Bearing stresses perpendicular to the grain of wood occur at beam supports or where loads from other members frame into the beam. See Example 6.16. The actual bearing stress is calculated by dividing the load or reaction by the contact area between the members or between the member and the connection bearing plate. The actual stress must be less than the allowable bearing stress

The allowable compressive stress perpendicular to grain is obtained by multiplying the tabulated value by a series of adjustment factors

where<span class="inlinemediaobject"><img alt="Image from book"> border="0"> height="16"> id="IMG_549"> src="http://images.books24x7.com/bookimages/id_15157/p30001e14g6_400001vpp.png"> title=""> width="24"></span> = allowable compressive (bearing) stress perpendicular to grain<i class="emphasis">F</i><sub<i class="emphasis">c</i></sub><sub?</sub> = tabulated compressive (bearing) stress perpendicular to grain<i class="emphasis">C</i><sub<i class="emphasis">M</i></sub> = wet service factor (<a class="chapterjump"> href="portalcontent.asp?bkid=15157&destid=445#445"> target="_parent">Sec. 4.14</a>)  = 1.0 for dry-service conditions, as in most covered structures.    Dry-service conditions are defined as    MC <span class="unicode">?</span> 19 percent for sawn lumber    MC < 16 percent for glulam<i class="emphasis">C</i><sub<i class="emphasis">t</i></sub> = temperature factor (<a class="chapterjump"> href="portalcontent.asp?bkid=15157&destid=464#464"> target="_parent">Sec. 4.19</a>)  = 1.0 for normal temperature conditions<i class="emphasis">C</i><sub<i class="emphasis">i</i></sub> = incising factor (<a class="chapterjump"> href="portalcontent.asp?bkid=15157&destid=466#466"> target="_parent">Sec. 4.20</a>)  = 1.0 for sawn lumber. (<i class="emphasis">Note:</i> The incising factor is not applicable to glulam.)<i class="emphasis">C</i><sub<i class="emphasis">b</i></sub> = bearing area factor (defined below)   = 1.0 is conservative for all cases

For sawn lumber a single value of F _{c ?} is listed for individual stress grades in the NDS Supplement. For glulams