PRACTICAL CONSIDERATIONS OF DOWEL BEARING STRENGTH AND ANNULAR RING FASTENER ORIENTATION

The orientation of the fastener with respect to annular growth rings c an affect the strength of laterally loaded wood connections. Connectio n properties are dependent on localized dowel bearing strength, which in turn is dependent on the specific gravity of the earlywood and late wood that constitute the annular rings. In the study reported here, do wel bearing strength was determined for matched specimens of three sof twood species (southern pine, Douglas-fir/larch, and spruce-pine-fir) using a 0.131-inch-(3.33-mm-) diameter nail. Tests were conducted with the nail oriented radially and tangentially with respect to the annul ar rings. Specific gravity, percentage of latewood, and number of ring s per inch were also determined for each specimen. Results illustrated that although the difference between radially and tangentially loaded dowel bearing strength can be significant, this difference is of no p ractical consequence. The combination of fastener size (in contact wit h many growth rings) and the relatively infrequent occurrence of very coarse- and flat-grained lumber resulted in nearly equal values of dow el bearing strength in the radial and tangential directions. Little co rrelation was found between dowel bearing strength and percentage of l atewood or number of rings per inch.