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TE C HN IC AL NOTE N UM BE R 236 UNTDSTATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORA Y MDSN5. WISCONSIN :REVISED er 1958 NAILWITHDRAWAL RESISTANCE 0fAMERICAN WOODS R is tnc e of a nail to dir ec t withdrawal f romnap related to the density or specific gravity of the wood, Lae I iaimter~af the nail, and the depth it has penetrated. The surface condition of the nail" adthe type of shank and point it has will also influence the withdrawal resistance. For bright common winre nails driven into the side grain of wood, the withdrawal resistance immediately after the nail is driven is given by the formula, 'p 6 6900 G5 2D, in which p represents the ultimate load per liel inch of penetration in the member holding the nail point; G the specific gravity of the wood based on weight and volume when ovenwdry; and D the diameter. of the nail in inches.' Relationships expressed by this equation are general and provide information on the relative withdrawal resistance of different species of wood. Certain species of wood, however, give test values that are somewhat hiher or lower than the equation values. Usually common knowledge of the characteristics of the nail, and of the species with particular refereneto tendency to split, will aid in deciding whether the withdrawal resistance will fall above or below the equation values. The general equation indicates that the dense, heavy woods offer greater nailwithdrawal resistance than the ones of lighter weight. This does not mean that the lighter species are not qualified for uses requiring high withdrawal resistance. As a rule, the lighter species do not split as readily as the dense ones; thus lighter woods offer an opportunity for increasing the diameter, length, and number of the nails to compensate for the wood's lower nailholding properties. In practically all species, nails driven into green wood and pulled before any seasoning takes place will offer about the same withdrawal resistance as nails driven into seasoned wood and pulled soon after driving. However, if common smooth shank nails are driven into green wood that is allowed to season or into seasoned wood that is subjected to cycles of wetting and drying before the nails are pulled, they lose a major part of their withdrawal resistance. In seasoned wood that is subjected only to r m o Ln evi 0, o r a,. o t a, o U (D oll CY* f m f m t f a, Ln 0 V4 V4 V4 V4 V4 :> r4 0 >1 W NO 00 4 Ln v4 v4 M 0% f M N v4 C11, 00 N '144 V N tn v4 N Lf) Ln N x 't 't in V 44 V q1t 11 Ln m 1 t Ln tn m V qqr m V m V ,11 14 en 4) . 04 0 (U to v 04 4) > ... . 0 r 4j 0 VX 0 N 0 ,4 U) u N W 4,.' 0 0 w k r4 4A ,4 $4 1 "4 r4 4) 14 0 41 N 4) bb r4 0 .$4 .;4 (d 44 $4 4.4 V4 V4 rd r* w r.1 P4 rA a V :3 be M 0 U) cd 0 0 W 0 0 4) 1 Q) 0 !> u u r4 L) u 4 04 $4 M W ;P 4) W 4) 1 1 0 0 10 r4 0 4) (U P4 0) UD N rCl rd 4 4 $4 0 0 0 0 0 a 14 ; l P 4 C Cd 0 m 0 0 r4 4 (U 4) 4 ,4 ,4 4 r4 .4 ,4 0 4) 0 04 01 131 Ia. ol 04 4 P4 04 04 134 a4 N 04 N Cd 94 > ,4 0 qtr a a. tn o tn en N N a. Ln N o w m N r4 4 f %0 .0 Ln Cil. 144 011. Ln w Ln I Ln m m V4 Ln tn %D C7% m v tn m w r4 N N N 4 ml r4 4 N "4 0.4 0.4 >1 P4 V4" Ln r (n Ln 'D r %0 Ln "qp en N Ln P4 00 'D P4 't Ln ^I en > Ln 'o 'D 44 0) 11 Ln %0 Ln Ln %0 r Ln %0 Ln tn %D "o r Ln Ln Ln Ln . r4 . (U $4 14 14 ,4 4 u bo U 4 Cd 0 E ,4 u u w 0 ".4 C4 $4 (u w Cd *j 0 'o 4 u 4 E E m Ia. r4 0 0 C4 V4 4 0 (t D Cr 0 0 0 n roA E E k 0 0. ,4 0 0 0 0 0 o ft I 0 Z w X4 r4 u u to 0 0 .0 u e 0 0 o o 0 E r4 0 0 0 r4 4 4 4 0 u u .4.4 tw cd W I (U IA u (J u u Cd M ol 4 C 0 0 04 4 4 4 44 M P M M U Q U W W W Z :Ij Z 0 0 U) (n F4 F4 >4 Nail diameter varies for different types of nails. )Here are diameters of bright common wire nails: PeGage Diameter Pennyr Gage Diameter 4 121/2 0.098 12 9 0.148 6 111/2 .113 16 8 .162 8 101/4 .131 20 6 .192 10 9 .148 480 1 . . ................. 440 4 0 0 .. . 7 360 i "320 200 60 ... ........ .. 034 a38 042 046 SO0 054 058 062 066 070 SPECIFIC GRAVITY Figure 1. Load required to withdraw common nails from wood of different specific gravities immediately after nails were driven. Specific gravity is based on weight and volume of ovendry wood. 3 UNIVERSITY OF FLORIDA 3 1262 09216 7922 ,moisture changes from normal atmospheric variations, the withdrawal resistance of smoothshank nails also diminishes in time. On the other hand, tests indicate that, when moisture conditions cause nails to rust, withdrawal resistance is very erratic; it may be regained or even increased over the immediate withdrawal resistance. Under all conditions of use, the withdrawal resistance of nails varies so widely that it is difficult to evaluate their behavior. The withdrawal loads for plain nails driven into wood that is subjected to wide alternating changes in moisture content maybe as much as 7 5 percent below the values given by the general formula. The specific gravity of various species of wood and their relative resistance to the withdrawal of smoothshank nails are given in table 1. There the numerical value of 6900 G512 has been calculated for each species. The load per inch of penetration immediately after driving may be obtained by multiplying this nailwithdrawal factor by the diameter, D. For example, table 1 shows a value of 790 D for an eightpenny common nail (0. 131 inch diameter) in ponderosa pine. Multiplying 790 times 0.131 gives a value of 103 pounds per inch of penetration. The curves in figure 1 show the relationship between load for common wire nails and the specific gravity of the wood. By using the specific gravity from table 1, the withdrawal resistance of a given size nail may be obtained directly from the curves. For example, to obtain the withdrawal resistance of an eightpenny (0.131inch diameter) common nail in ponderosa pine, follow the specific gravity line at 0.42 upward to the 8 D curve. A horizontal line from that point of intersection to the load scale shows a load of 103 pounds. The values given herein are for nails driven perpendicular to the grain of the wood. When the nail is driven parallel to the wood fibers into the end of the piece  withdrawal resistance in the softer woods drops to75 or even 50percentof the resistance obtained when the nail is driven perpendicular to the grain. The direction at which the nail is driven has less effect on the withdrawal resistance in dense woods than in softer woods. Slant driving of nails is usually superior to straight driving. Many other types of nails have been developed for ordin ary or special uses. These include annular grooved, spirally grooved, and coated or etched nails. In general, they have been developed to provide higher resistance to withdrawal than furnished by the common nail. Under conditions involving changes in the moisture content of the wood, annular grooved and spirally grooved nails provide considerably greater withdrawal resistance than the common wire nail. This is especially true of nails driven into green wood that subsequently seasons. 4 