Effect of Moisture 

Content on 

Nail Bearing 

Strength 

Douglas R. Rammer 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

Research 

Paper 

FPL−RP−591 
Abstract 

Current philosophy of lateral connection design strength is 

based on the yield theory that relates connection performance 

to fastener bending strength and wood dowel bearing 

strength. This study investigated the nail bearing properties 

of four species groupings, Southern Pine, yellow-cedar, 

Spruce–Pine–Fir, and maple, at various moisture content 

levels and different nail diameters. Spruce–Pine–Fir nail 

bearing strength specimens were tested at six different moisture contents (green, 19%, 15%, 12%, 9%, and 6%) and with 

three different nail diameters (3.33 mm (0.131 in.), 4.11 mm 

(0.162 in.), and 5.72 mm (0.225 in.)). An additional grouping 

was generated for 3.76-mm- (0.148-in.-) diameter nails at 

12% moisture content. Remaining species were tested with 

only a 4.11-mm- (0.162-in.-) diameter nail and reduced 

moisture content levels. The objective was to determine the 

effect of moisture content, specific gravity, grain orientation, 

and nail diameter on the nail bearing properties. Results 

indicate that grain orientation affected nail bearing stiffness 

and strength, but no statistically significant conclusion was 

drawn about the effect of nail diameter on bearing properties. 

Generally, the value of average bearing properties decreased 

as nail diameter increased. Expressions were developed 

relating the moisture content to nail bearing properties for 

each species and relating specific gravity and nail bearing 

properties at four moisture content levels.

Keywords: dowel, bearing strength, moisture content, nails, 

design criteria, connections 

February 2001 

Rammer, Douglas R. 2001. Effect of moisture content on nail bearing 

strength. Res. Pap. FPL-RP-591. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 22 p. 

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Contents 

 Page 

Introduction............................................................................1

Background............................................................................1

Effect of Moisture on Wood Strength................................1

Dowel Bearing Strength.....................................................1

Moisture Effects on Dowel Bearing Strength ....................2

Research Methods..................................................................3

Data Analysis.........................................................................4

Offset Analysis...................................................................4

Moisture Intersection Calculation......................................5

Results....................................................................................5

Specific Gravity .................................................................5

Moisture Content ...............................................................6

Parallel-to-Grain Nail Bearing Specimens.........................6

Perpendicular-to-Grain Nail Bearing Specimens ...............7

Observations ..........................................................................8

Failure Modes ....................................................................8

Load–Deformation Curves.................................................9

Discussion and Comparisons ...............................................10

Effect of Grain Orientation ..............................................10

Effect of Nail Diameter....................................................11

Effect of Moisture Content ..............................................12

Probability Distributions..................................................13

Specific Gravity–Nail Bearing Strength Relationship......16

Conclusions..........................................................................19

References............................................................................20

Appendix—Nonparametric Distributional Information .......21
Effect of Moisture Content 

on Nail Bearing Strength 

Douglas R. Rammer, Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

Introduction 

Currently in the United States, both nailed and bolted lateral 

connections are designed by the yield theory (AF&PA 1997, 

ASCE 1996). This theory relates the 5% diameter offset load 

to connection geometry, dowel bearing strength, and dowel 

bending yield strength. Wilkinson (1991) determined both 

bolt and nail bearing strength for several wood species. 

Unfortunately two species groupings, which accounted for 

40% of the nail data sets, were at a moisture content (MC) 

of about 6%. Because the application of the yield theory is 

relatively new in the United States, few studies have been 

conducted according to accepted ASTM test procedures 

that completely define the factors influencing nail bearing 

strength. One such factor is MC. 

The objective of this study was to determine the effect of 

MC and specific gravity on nail bearing properties. Also, 

comparisons were made to determine if nail bearing properties were affected by nail diameter and direction of loading 

relative to grain orientation. 

Background 

Effect of Moisture on Wood Strength 

The Wood Handbook (Forest Products Laboratory 1999) 

provides a general discussion of the effect of MC on clear 

wood strength properties. It has been widely accepted that as 

MC goes from the fiber saturation point (FSP) to dry, the 

strength properties of wood increase. However, as Green and 

Kretschmann (1994) discuss, there is growing evidence that 

different strength and stiffness properties are affected to 

varying degrees by changing levels of MC. For example, the 

bending modulus of elasticity (MOE) of clear Southern Pine 

increases linearly with drying from green to 4% MC, while 

MOE of compression parallel to grain increases linearly with 

drying from green to about 6% MC, then increases at a 

slower rate or remains constant with further drying. Ultimate 

tension stress, both parallel and perpendicular to grain, 

peaks in a range of 7% to 13% MC and then decreases with 

further drying. 

The FSP is the MC level at which all liquid water has been 

removed from the cell cavities but the woody cell wall 

remains saturated. It is generally assumed that material 

properties above the FSP do not change. Below the FSP, 

water is removed from the wood cell wall causing the 

mechanical properties to change. It has long been known that 

the FSP value and the MC level at which mechanical properties are observed to change are different. The MC level 

where mechanical properties are observed to change is called 

the intersection MC, Mp. 

Wilson (1932) proposed one of the first methods for calculating the Mp value. He made a log transformation of the dry 

data and fit a linear curve to the transformed data. The intersection between the dry linear curve and the average 

saturated property data established the Mp values for the 

property. 

Dowel Bearing Strength 

Only recently has an ASTM standard for evaluating dowel 

bearing strength been developed and accepted (ASTM 

1996). Therefore, only a limited amount of dowel bearing 

strength data has been generated according to this new 

ASTM standard. European countries standardized their 

dowel bearing testing procedure in the early 1990s 

(European Committee for Standardization 1993). This procedure defines the bearing strength using the maximum load 

or a limiting deformation of 5 mm. Additionally, the European dowel bearing test specimen encases the dowel with 

wood and allows flexibility in the dowel to occur, whereas 

the current ASTM standard does not. 

Smith and others (1988) determined that nail bearing strength 

is a function of both specific gravity and nail diameter. They 

used Sitka spruce, Scots pine, European redwood, European 

whitewood, and Canadian spruce–pine–fir for the softwood 

species with specific gravities between 0.4 and 0.5 and 

Malaysian keruing and South American greenheart for the 

hardwood species. These tropical hardwood species have a 

specific gravity about 0.75 and 1.00, respectively. For the 

softwoods, they used nail diameters of 2.65, 3.35, 4.00, 5.00, 

and 6.00 mm, and for the hardwoods, they used nail diameters of 3.55 and 6.00 mm. Based on these experimental 

results, they derived the following relationships for softwoods and tropical hardwoods: 
2 

for tropical hardwoods

6

0.071

for softwoods

6

0.048

0.28

0.036

−

−





 



 =





 



 =

d S

d S

ρ

ρ

where S is the maximum bearing strength (N/mm2), d is the 

nail diameter (mm), and ρ is the timber mass density (kg/m3

) 

with mass and volume at 13% MC. There was a difference 

between the parallel- and perpendicular-to-grain orientation, 

but since this difference was small, data were combined for 

the regression analysis. 

Wilkinson (1991) determined the dowel bearing strength for 

several wood species. His material ranged between 0.36 and 

0.52 in specific gravity and focused on 19.1-mm (0.75-in.) 

bolts and 4.11-mm (0.162-in.) nails. Expressions were developed that related the specific gravity and dowel diameter for 

bolts aligned parallel and perpendicular to grain and nails 

driven into side grain. These expressions were later accepted 

into the current wood construction specifications (AF&PA 

1997, ASCE 1996). Dowel bearing stress of nails that is 

applicable for both wood main and side member is 

1.84 Fe = 114.45G

where Fe is the nail bearing strength expressed in N/mm2 and 

G is the specific gravity defined using ovendry weight and 

volume. An FPL internal re-evaluation of Wilkinson’s nail 

data revealed that the specific gravity was miscalculated and 

two species groupings, Southern Pine and Spruce–Pine–Fir, 

had significantly lower MC values (6% lower). 

Pope and Hilson (1995) experimentally compared the ASTM 

D5764 and the EN 383 dowel test procedures using two sizes 

of bolts with loading applied parallel and perpendicular to 

grain. They concluded that ASTM and EN 383 procedures 

gave similar results for parallel-to-grain values but the 

EN 383 perpendicular-to-grain results were significantly 

greater than the ASTM values. 

Rammer (1999) evaluated the validity of using Wilkinson’s 

nail bearing strength expression for high-density wood species. Parallel-to-grain nail bearing tests were conducted using 

nails with two different diameters (3.33 and 6.2 mm) and two 

Guatemalan hardwoods with specific gravity values of 0.70 

and 0.76. Rammer showed that exploration of Wilkinson’s 

expression to higher specific gravity species is unwarranted 

and that the diameter of the nail had a statistically significant 

effect on the nail bearing strength. 

Moisture Effects on Dowel 

Bearing Strength 

Rammer and Winistorfer (2001) tested Southern Pine at 4%, 

6%, 12%, 19%, and green MC levels to develop an expression that relates parallel-to-grain bolt bearing strength to MC. 

Bolt bearing strength at 20% MC is related to the other four 

moisture levels by the following expressions: 

Fe @ 15% = 1.23(Fe @ 20%) 

Fe @ 12% = 1.36(Fe @ 20%) 

Fe @ 6% = 1.63(Fe @ 20%) 

Fe @ 4% = 1.72(Fe @ 20%) 

Rammer and Winistorfer (2001) validated this model by 

comparing it with previous Douglas-fir, Southern Pine, and 

Spruce–Pine–Fir nail bearing strength results at 6% and 

20+% MC. These tests were conducted on specimens with a 

routed groove nearly the same size as the nail; therefore, the 

moisture adjustments shown are valid for dowels with predrilled holes equal to or greater than the dowel diameter. 

In addition to Rammer and Winistorfer’s moisture expressions, Fahlbusch (1949) developed an expression to relate 

MC and parallel-to-grain dowel bearing strength. The relationship he developed used pine, ash, and linden solid wood 

and a 12-mm bolt and is valid between 5% and 30% MC. 

The following is Fahlbusch’s relationship: 

14

26 e12 e + = uf f u

where u is MC (%), feu is the peripheral hole strength 

(kg/cm2

) at MC u, and fe12 is the peripheral hole strength 

(kg/cm2

) at 12% MC. 

More recently, Koponen (1991) developed a bilinear model 

to describe the effect of MC on dowel bearing strength relationship for 12- to 20-mm-diameter bolts. Conducting tests 

on Finnish spruce that had an average specific gravity of 

0.48, Koponen varied the MC between 9% and green to 

arrive at the following dowel bearing strength expression: 

 fe = 46.7 − 1.35u when u < 22.5% 

 fe = 16.5 when u > 22.5%

where u is MC (%) and fe is dowel bearing strength in 

N/mm2

. He also developed a bilinear model for the effect of 

MC on stiffness. 

 k1 = 92 −3.9u when u < 19.7% 

k1 = 14.6 when u > 19.7% 

where k1 is the 10% to 40% maximum load secant stiffness. 

Koponen also developed an expression relating specific 

gravity to both dowel bearing strength and stiffness for all 

bolt diameters tested. 

All previous research focused on determining the effect of 

moisture on the parallel-to-grain dowel bearing strength with 

bolts, not with nails or perpendicular to grain. Research 

outlined here will investigate the effects of MC on both 

parallel- and perpendicular-to-grain dowel bearing strength, 
3 

nail diameter effects, distributional properties, and linear 

dowel bearing specific gravity relationships. 

Research Methods 

Four species groupings, Southern Pine (SP), yellow-cedar 

(YC), Spruce–Pine–Fir (SPF), and maple (M), were tested 

to determine nail bearing strength at several different MC 

levels. The SPF material was used to conduct a majority of 

the experimental study. One hundred 39- by 90-mm source 

SPF members were sorted by specific gravity into two groups 

of 50. From one group of 50 SPF specimens, all the 3.33- 

and 4.11-mm specimens were derived, and from the other 

group, all the 3.72- and 5.72-mm specimens were derived. 

Within each group, specimens for the various moisture conditions were cut from the same board with care taken to 

eliminate natural defects in the resulting material. No two 

specimens for given nail diameter and moisture level were 

derived from the same source piece. Matched parallel- and 

perpendicular-to-grain specimens for a similar nail diameter 

and moisture level were derived from adjacent source material (Fig. 1). Both SPF parallel- and perpendicular-to-grain 

nail bearing strengths were tested at six different MC levels 

(saturated, 19%, 17%, 12%, 9%, and 6%) and with three 

different nail diameters (3.33 mm (0.131 in.), 4.11 mm 

(0.162 in.), and 5.72 mm (0.225 in.)). An additional grouping 

was generated for 3.76-mm (0.148-in.) nail diameter at 12% 

MC. Large replication numbers were used to conduct a statistical evaluation on the effect of nail diameter and grain direction on nail bearing strength. 

To be consistent with Wilkinson’s original work, the remaining tests were conducted using a 4.11-mm- (0.162-in.-) diameter nail. The SP, YC, and M species were tested parallel 

and perpendicular to grain at the following moisture conditions: saturated, 17%, 12%, and 6%. An additional 9% MC 

for SP was added to better characterize the potential flattening of nail bearing strength for lower MC level, which was 

the response observed by Green and Kretschmann (1994) in 

other SP mechanical properties. The number of specimens 

and average sizes for the nail bearing tests are listed in 

Table 1. 

All the source material had MC levels below the fiber saturation point. A rewetting process was used for the saturated 

specimen to achieve a MC level greater than the fiber saturation point. Wood material was placed into a pressure-treating 

vessel. Water was introduced in the cylinders under pressure 

for several hours. A control specimen was removed, and an 

electronic moisture meter determined the MC. When the MC 

levels of the control specimens were significantly greater 

than FSP for that species, all the specimens were removed. 

From this point on, the saturated material was maintained in 

a wet condition during fabrication and testing. 

Specimen preparation followed procedures outlined in 

ASTM D 5764 Section 8.2.4 (ASTM 1996). Specimens were 

cut and clamped, and a pilot hole was drilled and then nailed. 

A pilot hole 75% the diameter of the shank was drilled prior 

to nailing. Specimens were nailed between 24 and 32 hours 

before testing. During the 24-hour waiting time, specimens 

remained in the appropriate conditioning room. For the 19% 

and saturated moisture conditions, specimens were placed in 

sealed plastic bags to minimize any drying effects during 

the 24-hour waiting period. 

The rate of testing was a constant 1.02-mm/min 

(0.04 in./min) for all specimens tested. This means that, on 

average, the 3.33-mm nail specimen failure times were 40% 

faster than the 5.76-mm nail test times. Deflection of the 

testing machine load head was measured with a linear 

Parallel-to-grain

Perpendicular-to-grain

50.8 mm

50.8 mm

50.8 mm 76.2 mm

Figure 1—Orientation of matched parallel- and 

perpendicular-to-grain specimens in source 

material. 
4 

variable differential transducer until the deformation exceeded 50% of the nail diameter or the loading apparatus 

touched the specimen. Load was measured to the nearest 

pound increment. Load and deformation readings were used 

to calculate the stiffness and the percentage offset yield 

loads. Figure 2 shows a parallel-to-grain and perpendicularto-grain specimen under load. 

After testing, MC and specific gravity values for each specimen were found in accordance with ASTM D4442 and 

ASTM D2395 procedures (ASTM 1995a,b). The entire 

specimen was used as the sample, and the size of the nail was 

subtracted for volume calculations. Specific gravity values 

are based on weight and volume after oven drying. 

Microscopic identifications indicated that the 100 source 

SPF members consisted of the following species: 45 Picea, 

29 Abies, and 26 yellow pine. 

Data Analysis 

Offset Analysis 

The 5%, 10%, 25%, and 50% diameter offset yield loads 

were determined for each specimen by the following 

procedure. Initial slope of the load–deformation curve is 

approximated by linearly regressing the data between 20% 

and 40% of the maximum load. The slope was then offset an 

Table 1—Summary of the number and sizes of specimens used for nail bearing tests

 Perpendicular-to-grain specimens Parallel-to-grain specimens 

Species 

Nail 

diameter 

(mm) 

Moisture 

content 

No. 

tested 

Width 

(mm) 

Depth 

(mm) 

Length 

(mm) 

No. 

tested 

Width 

(mm) 

Depth 

(mm) 

Length 

(mm) 

Yellow-cedar 4.11 6% 24 24.9 50.8 49.0 33 24.9 50.8 74.4 

 12% 26 25.1 50.9 50.7 34 25.3 51.0 74.1 

 17% 23 25.6 50.7 48.3 34 25.6 50.7 74.0 

 Saturated 24 26.0 50.9 50.9 34 26.1 51.0 76.8 

Maple 4.11 6% 29 27.1 50.7 50.2 30 27.1 50.8 77.0 

 12% 30 31.6 51.0 48.7 30 31.6 51.5 74.1 

 17% 29 31.8 51.0 48.6 30 31.7 51.0 74.0 

 Saturated 30 25.6 50.8 50.6 31 25.6 51.1 77.0 

Southern Pine 4.11 6% 37 37.4 50.8 76.1 37 37.5 50.4 76.3 

 9% 37 37.7 50.8 76.2 37 37.6 50.5 76.4 

 12% 42 37.8 51.3 74.9 43 37.8 50.6 75.9 

 17% 37 38.2 50.8 75.5 37 38.1 51.1 76.1 

 Saturated 37 39.6 50.8 75.8 37 39.6 52.7 76.2 

Spruce–Pine–Fir 3.33 6% 49 25.6 51.0 51.3 45 25.4 50.6 76.4 

 9% 48 25.7 50.9 50.8 50 25.7 51.3 76.1 

 12% 48 25.4 50.6 50.9 49 25.4 50.8 76.1 

 17% 48 25.4 50.9 50.7 49 25.2 50.5 76.2 

 Saturated 48 25.9 50.9 50.9 49 25.8 51.8 76.0 

Spruce–Pine–Fir 3.76 12% 46 25.4 50.6 51.0 31 25.4 50.9 76.2 

Spruce–Pine–Fir 4.11 6% 49 25.4 50.9 51.1 49 25.5 50.7 76.3 

 9% 49 25.8 50.9 50.9 48 25.7 51.4 76.1 

 12% 49 25.5 50.6 51.0 49 25.5 50.9 76.2 

 17% 50 25.5 50.9 50.8 50 25.3 50.6 76.1 

 19% 50 25.6 50.9 51.9 50 25.5 52.2 76.4 

 Saturated 49 26.0 50.9 50.8 50 25.8 51.8 76.2 

Spruce–Pine–Fir 5.76 6% 44 25.4 51.0 51.2 39 25.3 51.1 76.4 

 9% 47 25.8 50.9 50.7 47 25.7 51.4 76.1 

 12% 46 25.4 50.6 51.0 47 25.4 50.9 76.2 

 17% 46 25.4 50.9 50.8 47 25.4 51.1 76.1 

 Saturated 46 26.1 50.9 51.1 47 26.0 51.9 75.9 
5 

amount equal to 5%, 10%, 25%, and 50% of the nail diameter used for that test. The point of intersection of the offset 

line for a given percentage and the load–deformation curve 

determined the yield load for that given offset percentage. 

If the percentage-offset line did not intersect the load–

deformation curve, the maximum load of the test was used as 

the yield load. Figure 3 illustrates the procedure for the 5% 

offset line. Nail bearing strength values were calculated by 

dividing yield load by the product of fastener diameter and 

loaded length of the fastener. Stiffness, for 20% to 40% of 

the maximum load, is calculated using the slope of the linear 

regression divided by the product of fastener diameter and 

loaded length of the fastener. 

Moisture Intersection Calculation

A procedure similar to Wilson’s (1932) historic method was 

used to establish the Mp values for all the material tested. For 

a given species grouping, nail diameter, and MC level, the 

data were adjusted to a common specific gravity value using 

the derived linear specific gravity–nail bearing strength 

relationship for each given test set. Common specific gravity 

was the average value for the species, orientation, and nail 

diameter considered. Once these data were adjusted to a 

common specific gravity value, a linear and quadratic curve 

was best-fit to the data. Based both on the correlation coefficient and visual interpretation, a curve was chosen that best 

represented the data. Moisture intersection Mp was determined as that MC where the average saturated result intersected the best-fit curve for a given species, grain orientation, 

and nail diameter. 

Results 

The average, coefficient of variation (COV), maximum, and 

minimum specific gravity and MC data for all the moisture 

groupings and wood species are summarized in Tables 2 and 

3. Average stiffness and 5% diameter offset nail bearing 

strength values are listed in Tables 4 and 5 for parallel- and 

perpendicular-to-grain loading, respectively. Detailed nonparametric distributional information for the 5% diameter 

offset strength is given in the Appendix for all test groupings. 

Specific Gravity 

Average specific gravity for each species, MC level, and 

orientation is given in Table 2 along with COV, maximum, 

and minimum observed values. The average, maximum, and 

minimum specific gravity values are fairly consistent for each 

wood species regardless of MC grouping or grain orientation. 

The SPF COV values are greater than the other test species, 

but this is expected since the SPF grouping consists of 

several wood species. The average range of test specimen 

Figure 2—Nail bearing test configuration (a) parallel to 

grain and (b) perpendicular to grain. 

Figure 3—Offset procedure. 
6 

specific gravity was 0.42 to 0.69 and largely covers the range 

of specific gravity used in typical wood construction in the 

United States. 

Moisture Content 

Average MC levels for each species, nail diameter, nominal 

MC level, and orientation are given in Table 3 along with 

COV, maximum, and minimum observed values. The average, maximum, and minimum moisture values are tightly 

banded for the lower MC values, but as the target moisture 

level increased, the variation of MC values increased. 

Saturated conditions were the most variable, but all 

specimens achieved MC levels above the generally assumed 

30% FSP. 

Parallel-to-Grain Nail 

Bearing Specimens 

Mean and COV values for 20% to 40% of maximum load 

stiffness and 5% diameter offset strength for each species and 

nail size loaded parallel to grain are listed in Table 4. Stiffness increased with decreasing MC and was the most variable bearing property. The 5% diameter offset bearing 

strength values decreased with increasing MC, and the COV 

for these nails at all MC levels are within the range of 

Table 2—Mean, coefficient of variation (COV), minumum, and maximum data for specific gravitya

Specific gravity 

Parallel to grain Perpendicular to grain 

Species 

Nail 

diameter 

(mm) 

Moisture 

content Mean 

COV 

(%) 

Minimum Maximum Mean COV 

(%) 

Minimum Maximum 

Yellow-cedar 4.11 6% 0.51 8.3 0.43 0.61 0.52 6.6 0.41 0.57 

 12% 0.51 7.5 0.42 0.61 0.50 8.2 0.43 0.58 

 17% 0.50 8.2 0.42 0.59 0.51 7.2 0.42 0.55 

 Saturated 0.52 7.9 0.44 0.62 0.51 6.9 0.42 0.55 

Maple 4.11 6% 0.69 8.3 0.55 0.81 0.69 8.5 0.53 0.80 

 12% 0.69 8.1 0.52 0.81 0.70 9.5 0.50 0.87 

 17% 0.70 8.6 0.53 0.85 0.70 8.5 0.53 0.82 

 Saturated 0.68 8.9 0.57 0.84 0.69 9.3 0.55 0.85 

Southern Pine 4.11 6% 0.60 9.8 0.52 0.73 0.61 9.7 0.52 0.72 

 9% 0.60 8.8 0.51 0.71 0.60 9.0 0.51 0.70 

 12% 0.60 9.9 0.50 0.77 0.60 10.1 0.50 0.71 

 17% 0.61 11.2 0.49 0.74 0.61 11.0 0.48 0.72 

 Saturated 0.60 9.3 0.51 0.73 0.60 9.7 0.50 0.72 

Spruce–Pine–Fir 3.33 6% 0.42 15.4 0.29 0.57 0.43 14.8 0.29 0.56 

 9% 0.43 13.8 0.30 0.55 0.43 14.4 0.30 0.56 

 12% 0.42 14.5 0.30 0.56 0.42 14.1 0.30 0.55 

 17% 0.42 13.4 0.30 0.56 0.43 15.4 0.30 0.64 

 Saturated 0.43 14.5 0.30 0.56 0.42 14.0 0.32 0.56 

Spruce–Pine–Fir 3.76 12% 0.43 14.6 0.31 0.54 0.43 14.9 0.30 0.55 

Spruce–Pine–Fir 4.11 6% 0.42 13.6 0.29 0.56 0.42 14.0 0.29 0.55 

 9% 0.42 14.5 0.29 0.56 0.42 14.4 0.29 0.56 

 12% 0.42 14.0 0.29 0.55 0.42 14.1 0.30 0.58 

 17% 0.42 13.6 0.30 0.56 0.42 14.0 0.30 0.56 

 19% 0.42 13.7 0.30 0.55 0.42 13.5 0.30 0.54 

 Saturated 0.42 13.6 0.31 0.55 0.42 13.2 0.31 0.54 

Spruce–Pine–Fir 5.76 6% 0.43 14.4 0.29 0.57 0.43 13.7 0.29 0.54 

 9% 0.42 13.8 0.30 0.53 0.42 14.7 0.30 0.57 

 12% 0.42 13.1 0.32 0.53 0.42 12.5 0.32 0.50 

 17% 0.43 13.4 0.30 0.54 0.43 14.1 0.29 0.55 

 Saturated 0.43 13.5 0.27 0.53 0.42 13.9 0.28 0.53 

a

Specific gravity based on ovendry weight divided by ovendry volume. 
7 

Wilkinson’s findings. Effect of MC on the 5% diameter 

offset bearing strength is shown in Figures 4a through 9a. In 

these figures, saturated specimen results are plotted at the 

moisture intersection point Mp. These figures show that 

parallel-to-grain nail bearing strength generally increases as 

the MC decreases. SP parallel-to-grain specimens showed a 

decrease in 5% bearing strength for the 6% MC level. Green 

and Kretschmann (1994) noted a similar response in other SP 

mechanical properties. The average ratio of the 5% diameter 

offset strength to three different offset values, 10%, 25%, and 

50% for each nail size and MC are shown in Table 4. Results 

indicate that the 10%, 25%, and 50% offset values are generally greater than the 5% offset values. For all results, the 

10% offset load is 3.8% greater, the 25% offset load is 6.4% 

greater, and the 50% offset load is 7.7% greater than the 5% 

offset load. 

Perpendicular-to-Grain Nail 

Bearing Specimens 

Average and COV values for 20% to 40% of maximum load 

stiffness and 5% diameter offset strength for each species and 

nail size loaded perpendicular to grain are listed in Table 5. 

Stiffness increased with decreasing MC and was the most 

variable bearing property. The 5% diameter offset 

bearing strength values decreased with increasing MC, and 

Table 3—Mean, coefficient of variation (COV), minumum, and maximum data for moisture content 

 Moisture content 

Parallel to grain Perpendicular to grain 

Species 

Nail 

diameter 

(mm) 

Moisture 

content 

Mean 

(%) 

COV 

(%) 

Minimum 

(%) 

Maximum 

(%) 

Mean 

(%) 

COV 

(%) 

Minimum 

(%) 

Maximum (%) 

Yellow-cedar 4.11 6% 6.8 2.7 6.5 7.2 6.8 4.0 6.5 7.4 

 12% 12.4 2.3 11.9 13.0 12.7 2.3 12.1 13.2 

 17% 17.8 2.1 17.3 18.5 17.1 12.6 7.3 18.1 

 Saturated 80.9 22.6 39.4 110.2 86.6 22.8 44.4 117.6 

Maple 4.11 6% 8.0 4.2 7.1 8.7 7.6 4.3 7.2 8.5 

 12% 14.3 1.9 13.8 14.9 14.4 1.7 13.7 14.8 

 17% 18.1 6.2 17.0 21.9 18.9 6.8 16.9 21.8 

 Saturated 90.6 15.7 56.5 115.2 92.0 13.5 67.1 116.7 

Southern Pine 4.11 6% 6.3 2.9 6.0 6.6 6.2 3.1 5.8 6.5 

 9% 9.3 2.2 8.7 9.6 9.6 2.4 8.6 9.9 

 12% 11.0 5.6 9.4 11.9 10.8 5.8 9.6 11.9 

 17% 17.4 5.4 15.8 19.4 17.0 5.94 15.5 18.9 

 Saturated 114.2 13.2 86.9 143.2 114.7 13.46 77.6 138.9 

Spruce–Pine–Fir 3.33 6% 6.2 6.3 5.2 6.9 6.3 9.3 3.3 7.1 

 9% 8.9 6.7 7.1 9.7 9.0 5.9 7.4 9.8 

 12% 11.2 9.6 8.8 13.2 11.3 9.8 8.7 13.1 

 17% 16.7 13.5 11.2 21.3 16.5 13.3 11.6 21.2 

 Saturated 104.8 39.9 36.9 214.3 136.9 30.1 63.0 226.1 

Spruce–Pine–Fir 3.76 12% 11.2 10.4 8.3 12.7 11.3 9.7 8.4 13.2 

Spruce–Pine–Fir 4.11 6% 6.4 4.7 5.7 6.9 6.2 7.2 5.1 7.0 

 9% 8.8 6.7 6.8 9.6 8.9 6.9 6.8 9.8 

 12% 11.2 9.9 8.5 12.8 11.4 18.2 8.3 23.2 

 17% 16.6 13.6 11.4 21.2 16.6 13.6 11.7 21.7 

 19% 17.5 10.8 12.3 21.1 17.7 10.1 12.8 21.2 

 Saturated 106.0 38.3 34.6 226.3 135.6 27.8 56.2 226.7 

Spruce–Pine–Fir 5.76 6% 6.6 5.8 5.5 7.1 6.4 6.7 4.9 7.0 

 9% 9.1 6.7 6.9 10.0 9.1 7.0 7.0 10.9 

 12% 11.4 9.0 8.7 13.0 11.3 8.5 8.4 12.8 

 17% 16.5 11.2 13.2 20.2 16.5 14.1 12.8 21.1 

 Saturated 108.6 38.9 59.0 236.9 132.7 30.5 76.1 249.0 
8 

the COVs for these nails at these MC levels are within the 

range of Wilkinson’s findings. Effect of MC on the perpendicular-to-grain 5% diameter offset bearing strength is shown 

in Figures 4b through 9b. In these figures, saturated specimen 

results are plotted at the moisture intersection point, Mp. 

Again, these figures show that, generally, perpendicular-tograin nail bearing strength increases as the MC decreases. 

The average ratio of the 5% strength to three different offset 

values, 10%, 25%, and 50%, for each nail size and MC are 

shown in Table 4. Results indicate that the 10%, 25%, and 

50% offset values are greater than the 5% offset values. For 

all the results, the 10% offset load is 12.0% greater, the 25% 

offset load is 26.6% greater, and the 50% offset load is 

28.5% greater than the 5% offset load. 

Observations 

Failure Modes 

Two failure modes were observed for specimens loaded 

parallel to grain (Fig. 10a,b), and two different failure modes 

were observed for specimens loaded perpendicular to grain 

(Fig. 10c,d). For parallel-to-grain loading, the predominant 

failure mode was localized crushing or bearing of the wood 

directly under the nail. This failure occurred in 78% of all 

parallel-to-grain tests. For the remaining specimens at failure, 

a split developed directly under the nail on one or both sides 

of the specimen. For all wood species, the occurrence of the 

splitting failure modes typically increased as the MC of the 

Table 4—Parallel-to-grain nail bearing results 

Stiffness Bearing strength Offset load ratios Failure observations 

Species 

Nail 

diameter 

(mm) 

Moisture 

content 

Mean 

(N/mm3

) 

COV 

(%) 

Mean 

(MPa) 

COV 

(%) 10%/5% 25%/5% 50%/5% Bearing Splitting 

Yellow-cedar 4.11 6% 156.5 21.4 56.84 15.6 1.000 0.993 1.029 8 25 

 12% 152.2 26.5 42.38 15.4 1.026 1.035 1.060 28 6 

 17% 106.0 29.8 31.01 14.5 1.050 1.087 1.111 30 4 

 Saturated 37.6 25.3 23.21 19.1 1.026 1.043 1.049 34 0 

Maple 4.11 6% 235.3 19.9 79.67 16.3 1.022 1.035 1.035 19 11 

 12% 101.3 32.8 48.09 16.4 1.015 1.039 1.052 28 2 

 17% 107.8 24.3 44.76 16.9 1.023 1.051 1.067 29 1 

 Saturated 50.4 33.3 31.02 14.7 1.077 1.085 1.085 31 0 

Southern Pine 4.11 6% 115.6 44.1 47.20 27.6 0.993 1.058 1.058 17 20 

 9% 110.8 31.2 49.22 18.8 1.037 1.020 1.049 17 20 

 12% 105.7 34.9 46.59 19.4 1.028 1.040 1.040 — — 

 17% 87.4 34.8 34.31 16.7 1.046 1.073 1.082 35 2 

 Saturated 36.9 40.8 24.50 16.5 1.033 1.043 1.056 37 0 

Spruce–Pine–Fir 3.33 6% 78.6 38.4 34.94 22.3 1.013 1.000 1.040 27 18 

 9% 107.6 32.3 34.51 24.2 1.028 1.017 1.054 34 16 

 12% 80.0 41.0 28.89 19.4 1.022 1.056 1.059 46 3 

 17% 60.6 38.4 23.66 17.4 1.045 1.089 1.096 48 1 

 Saturated 27.2 53.3 16.10 25.3 1.037 1.078 1.085 49 0 

Spruce–Pine–Fir 3.76 12% 77.8 38.4 29.66 24.2 1.022 1.040 1.040 26 5 

Spruce–Pine–Fir 4.11 6% 71.0 44.8 32.61 30.2 1.030 1.072 1.103 17 32 

 9% 85.9 48.0 32.62 26.5 1.035 1.028 1.059 29 19 

 12% 72.7 40.8 27.68 26.0 1.055 1.055 1.055 35 14 

 17% 52.5 37.2 22.54 22.0 1.054 1.106 1.111 46 4 

 19% 53.2 43.5 22.30 20.7 1.065 1.109 1.124 48 2 

 Saturated 22.5 49.1 15.59 29.0 1.044 1.084 1.098 49 1 

Spruce–Pine–Fir 5.76 6% 76.4 42.1 30.91 30.7 1.074 1.133 1.140 11 28 

 9% 60.8 49.0 30.34 23.0 1.072 1.102 1.133 25 22 

 12% 75.8 29.6 31.95 19.0 1.049 1.086 1.091 41 6 

 17% 54.9 39.8 18.42 21.2 1.093 1.173 1.176 46 1 

 Saturated 9.4 46.7 14.35 22.2 1.040 1.080 1.089 47 0 
9 

specimens changed from saturated to 6% with the greatest 

occurrence at the 6% MC level. The number of bearing and 

splitting type failures for a given species, nail diameter, and 

MC are listed in Table 4. 

For perpendicular-to-gain loading, the predominant failure 

mode was localized crushing of the wood fibers directly 

under the nail (Fig. 10c). This failure mode occurred in 79% 

of all the perpendicular-to-grain tests. Remaining specimens 

failed by the development of a split from either side or both 

sides of the specimens at roughly the same level as the bottom of the nail (Fig. 10d). The occurrence of the splitting 

failure increased as the MC decreased for the YC, M, and SP 

specimens but was different for the SPF specimens. For SPF 

specimens with 3.33- and 4.11-mm nails, the incidence of 

splitting increased with increased moisture levels and was 

nearly constant for SPF specimens tested with a 5.76-mm 

nail. The number of bearing and splitting type failures for a 

given species, nail diameter, and MC are listed in Table 5. 

Load–Deformation Curves 

Representative load versus head displacement curves are 

plotted at 6%, 12%, and saturated MC conditions for parallel- and perpendicular-to-grain loading with a 4.11-mm nail 

of matched SPF specimens (Fig. 11). The 5% diameter offset 

lines are plotted on the curves to give a reference point for 

further discussion. Splitting and peeling failure responses are 

Table 5—Perpendicular-to-grain nail bearing results 

Stiffness Bearing strength Offset load ratios Failure observations 

Species 

Nail 

diameter 

(mm) 

Moisture 

content 

Mean 

(N/mm3

) 

COV 

(%) 

Mean 

(MPa) 

COV 

(%) 10%/5% 25%/5% 50%/5% Bearing Peeling 

Yellow-cedar 4.11 6% 55.8 38.1 35.55 15.88 1.095 1.258 1.282 21 3 

 12% 40.7 38.9 27.62 23.25 1.126 1.340 1.358 23 3 

 19% 25.1 34.4 21.03 17.67 1.126 1.306 1.332 16 7 

 Saturated 10.9 30.2 14.49 27.7 1.103 1.216 1.218 23 1 

Maple 4.11 6% 109.2 29.1 60.08 19.0 1.131 1.379 1.410 25 4 

 12% 76.7 35.0 46.99 20.4 1.131 1.380 1.426 26 4 

 19% 57.3 34.2 39.43 20.0 1.127 1.343 1.370 28 1 

 Saturated 18.87 36.3 21.29 26.5 1.156 1.330 1.336 29 1 

Southern Pine 4.11 6% 47.3 19.3 49.90 19.9 1.121 1.222 1.247 30 7 

 9% 53.2 21.7 45.36 16.9 1.114 1.251 1.259 29 8 

 12% 47.8 21.3 40.08 17.0 1.125 1.317 1.382 — — 

 17% 24.8 28.6 26.39 17.0 1.135 1.263 1.266 37 0 

 Saturated 10.2 27.9 15.30 19.1 1.113 1.230 1.256 37 0 

Spruce–Pine–Fir 3.33 6% 36.6 47.0 23.70 34.6 1.133 1.275 1.295 48 1 

 9% 37.2 42.8 24.33 29.6 1.096 1.234 1.252 44 6 

 12% 32.0 43.8 21.61 26.5 1.124 1.263 1.270 44 4 

 17% 19.7 38.5 17.51 25.9 1.141 1.325 1.329 41 7 

 Saturated 7.2 34.0 11.21 30.3 1.163 1.360 1.395 37 11 

Spruce–Pine–Fir 3.76 12% 29.8 39.0 20.80 22.4 1.109 1.239 1.236 41 5 

Spruce–Pine–Fir 4.11 6% 28.1 40.6 22.68 30.6 1.119 1.261 1.295 45 4 

 9% 30.6 43.6 22.45 27.5 1.102 1.248 1.255 45 4 

 12% 25.3 42.2 20.45 26.8 1.119 1.247 1.268 38 11 

 17% 17.2 43.1 16.19 26.5 1.119 1.225 1.228 34 16 

 19% 14.9 33.1 15.51 24.3 1.116 1.204 1.211 21 29 

 Saturated 5.6 28.3 8.71 32.1 1.166 1.332 1.370 39 10 

Spruce–Pine–Fir 5.76 6% 25.5 41.8 22.39 24.7 1.081 1.178 1.185 23 21 

 9% 23.2 47.3 20.44 25.6 1.087 1.178 1.182 20 27 

 12% 21.2 40.6 18.82 21.3 1.065 1.119 1.145 23 23 

 17% 13.2 32.4 13.13 21.4 1.129 1.210 1.216 24 22 

 Saturated 4.3 34.4 6.95 27.6 1.128 1.251 1.265 34 12 
10 

noted on Figure 11a for the 6% MC condition specimens 

because the occurrence of this type of failure was greatest at 

the lower moisture conditions. Bearing type failure response, 

which occurred in 79% of all tests, is shown in Figure 11b 

and 11c. All figures indicate that parallel-to-grain specimens 

typically had a substantial region of nearly constant load with 

increasing deformation, with the 5% offset line regularly 

intersecting the curve in this region. Therefore, differences 

between the 5% offset line and other offset levels are relatively small. Ratios listed in Table 4 indicate that the average 

difference between the 5% and 50% offset loads is 7.7% for 

all specimens with a maximum difference of 17.6% for 

5.76-mm-diameter nails in saturated SPF. 

Perpendicular-to-grain loaded specimens have a load versus 

head deformation curve that typically monotonically increases until the testing is concluded by a deflection limit or 

the load-head touching the specimen. When a splitting failure 

occurred, the specimen still had the ability to sustain higher 

load. It is hypothesized that the measured deformation is 

largely comprised of the axial response of the wood 

specimen and that the actual embedment of the nail into the 

wood is significantly smaller. Since the load is always increasing during the test, ratios of the 5% offset load to other 

offset loads increase as the percentage offset increases. Ratios listed in Table 5 indicate that the average difference 

between the perpendicular-to-grain 5% and 50% offset loads 

is 28.5% for all specimens with a maximum difference of 

42.6% for 4.11-mm-diameter nails in M at 12% MC. 

Discussion and Comparisons 

Effect of Grain Orientation 

The number of replicates allowed for a statistical comparison 

of the effect of grain orientation on 20% to 40% stiffness and 

nail bearing strength. For each wood species at each MC 

level and nail diameter, t-tests, at 0.05 level of significance 

were performed. Comparisons indicated that grain orientation 

has a statistically significant effect on stiffness for all considered combinations and has a statistically significant effect on 

nail bearing strength except for 12% MC M, 6% SP, and 9% 

Figure 4—Effect of moisture content on the (a) paralleland (b) perpendicular-to-grain 5% nail bearing 

strength of yellow-cedar using a 4.11-mm nail. 

Figure 5—Effect of moisture content on the (a) paralleland (b) perpendicular-to-grain 5% nail bearing 

strength of maple using a 4.11-mm nail. 
11 

SP comparisons (Tables 6 and 7). Ratios of the parallel and 

perpendicular stiffness and bearing strength were calculated 

(Tables 6 and 7). Stiffness ratios are highly variable, but with 

some exception, the ratio decreased as the MC levels went 

from saturated to 6%. Strength ratios were also variable, but 

the average value for each MC level 17% and lower ranged 

between 1.34 and 1.36. These average ratios included ratios 

that were statistically insignificant. The average strength ratio 

for saturated specimens was 1.66. In general, except for three 

cases, both the stiffness and bearing strength parallel-to-grain 

values were greater than matched perpendicular specimens. 

Effect of Nail Diameter 

For the SPF grouping, three different nail diameters were 

tested at each MC to determine if the nail diameter had a 

significant affect on stiffness or bearing strength. An analysis 

of variance (ANOVA) was conducted using a 0.05 level of 

significance and Tukey’s studentized test for multiple comparisons. Table 8 summarizes the ANOVA results for both 

stiffness and nail bearing strength for each MC tested. 

Numbers in the table represent the average stiffness or nail 

bearing strength values. A common underline under adjacent 

values indicates there is no significant difference between the 

values at a 0.05 level of significance. A common underline 

under three values indicates no significant difference between all three values. Stiffness results for tested nails in SPF 

were similar for at least two nail diameters at all moisture 

conditions but two. Parallel-to-grain stiffness was similar in 

most cases except one, but this was not the case for perpendicular-to-grain stiffness. Although some values were similar, 

the 3.33-mm nail stiffness was always greater than the 

4.11-mm nail values. Also, the 4.11-mm nail stiffness was 

always greater than the 5.76-mm nail stiffness. Bearing 

strength results were similar at each MC for a least two nail 

diameters, except one — the perpendicular-to-grain loading 

of saturated specimen. In all cases, the 3.33- and 4.11-mmdiameter nails (a 0.78-mm-diameter difference) gave similar 

results. Differences were only noticed between the 5.76-mmdiameter nail and the other nail diameters, which differed in 

diameter by a minimum of 1.65 mm. This indicates that the 

number of replicates was not great enough to significantly 

Figure 6—Effect of moisture content on the (a) paralleland (b) perpendicular-to-grain 5% nail bearing strength 

of Southern Pine using a 4.11-mm nail. 

Figure 7—Effect of moisture content on the (a) paralleland (b) perpendicular-to-grain 5% nail bearing strength 

of Spruce–Pine–Fir using a 3.33-mm nail. 
12 

distinguish the difference between the 3.33- and 4.11-mmdiameter nail bearing strength results. The ANOVA results 

did not conclusively determine that all nail diameters had a 

significant effect on nail bearing strength, but average values 

decreased as the nail diameter increased. For all specimens, 

the 3.33- and 4.11-mm nail bearing values were 19% and 

10%, respectively, higher than the 5.76-mm nail results. 

Effect of Moisture Content 

As shown in Figures 4 to 9, nail bearing strength generally 

increases with decreasing MC. To determine the moisture 

relationship for nail bearing stiffness, each data set for a 

given nail diameter and species was adjusted to a common 

specific gravity. The common value was the average specific 

gravity for a given diameter and species. Data were adjusted 

to this common value by conducting a linear regression of the 

data at each MC and using this relationship to adjust the data 

to the common specific gravity for the set. 

With this adjusted nail bearing stiffness data, linear and 

quadratic polynomials were fitted to data with a MC of 17% 

and lower. Intersection MC, Mp, values were found by substituting the average saturated nail bearing stiffness into the 

visually best-fitting expression. Final MC–nail bearing stiffness relationships were determined by refitting the polynomial expressions to all the data after shifting the saturated 

data set to the intersection MC. The criteria to determine 

which polynomial best represented the interaction were based 

on both the coefficient of determination and a visual 

interpretation of the curves plotted on the data. A linear 

expression was preferred because it would be simpler to 

implement into current practice. Table 9 lists the coefficients 

for the best-fit MC–nail bearing stiffness expression, r

2

, and 

moisture intersection for each species and grain orientation. 

For the SPF grouping, an expression was developed for the 

pooled nail sizes in the parallel and perpendicular grain 

directions. In all cases, MC was negatively correlated 

with stiffness. 

Figure 8—Effect of moisture content on the (a) paralleland (b) perpendicular-to-grain 5% nail bearing strength 

of Spruce–Pine–Fir using a 4.11-mm nail. 

Figure 9—Effect of moisture content on the (a) paralleland (b) perpendicular-to-grain 5% nail bearing 

strength of Spruce–Pine–Fir using a 5.76-mm nail. 
13 

A similar technique was used to determine the effect of MC 

on nail bearing strength for each material species. Table 10 

lists the coefficient for the best-fit MC–nail bearing strength 

expression, r

2

, and moisture intersection for each species and 

grain orientation. For the SPF grouping, an expression was 

developed for the pooled nail sizes in the parallel and perpendicular grain direction. In all cases, MC was negatively 

correlated with nail bearing. 

Calculated Mp values (Tables 9 and 10) for the different 

species are in line with Wilson’s (1932) published values for 

mechanical properties, 21% for Southern Pine, 24% for red 

pine, and 27% for Sitka spruce. The last two species are 

included in the SPF species grouping. 

Probability Distributions 

As the wood building design community moves toward a 

load and resistance design philosophy, underlying strength 

Figure 10—Failure modes parallel to grain (a) bearing 

and (b) splitting, and perpendicular to grain (c) bearing 

and (d) peeling. 

Figure 11—Representative load versus head deformation curves for (a) 6% moisture content, (b) 12% 

moisture content, and (c) saturated moisture condition. 
14 

Table 6—Statistical comparision of the effect of grain orientation on nail bearing stiffness 

t-tests for each moisture contenta Ratio for each moisture content 

Species 

Diameter 

(mm) 6% 9% 12% 17% Sat. 6% 9% 12% 17% Sat. 

Yellow-cedar 4.1 Yes — Yes Yes Yes 2.80 — 3.74 4.22 3.45 

Maple 4.1 Yes — Yes Yes Yes 2.15 — 1.32 1.88 2.67 

Southern Pine 4.1 Yes Yes Yes Yes Yes 2.17 2.32 2.24 3.53 3.64 

Spruce–Pine–Fir 3.3 Yes Yes Yes Yes Yes 2.15 2.89 2.49 3.08 3.80 

Spruce–Pine–Fir 4.1 Yes Yes Yes Yes Yes 2.52 2.81 2.87 3.06 4.01 

Spruce–Pine–Fir 5.7 Yes Yes Yes Yes Yes 3.01 2.62 3.57 4.15 2.17 

a Yes indicates a statistically significant difference between the means at a 0.05 level of confidence. 

Table 7—Statistical comparision of the effect of grain orientation on nail bearing strength 

t-tests for each moisture contenta Ratio for each moisture content 

Species 

Diameter 

(mm) 6% 9% 12% 17% Sat. 6% 9% 12% 17% Sat. 

Yellow-cedar 4.1 Yes — Yes Yes Yes 1.60 — 1.53 1.47 1.60 

Maple 4.1 Yes — No Yes Yes 1.33 — 1.02 1.14 1.46 

Southern Pine 4.1 No No Yes Yes Yes 0.95 1.09 1.16 1.30 1.60 

Spruce–Pine–Fir 3.3 Yes Yes Yes Yes Yes 1.47 1.42 1.34 1.35 1.44 

Spruce–Pine–Fir 4.1 Yes Yes Yes Yes Yes 1.44 1.45 1.35 1.39 1.79 

Spruce–Pine–Fir 5.7 Yes Yes Yes Yes Yes 1.38 1.48 1.70 1.40 2.06 

a Yes indicates a statistically significant difference between the means at a 0.05 level of confidence. 

Table 8—ANOVA statistical comparision of the effect of nail diameter on nail bearing stiffness and strength for SPF 

Mean stiffness values for each 

nail diameter (N/mm3

) 

Mean 5% diameter offset strength for each 

nail diameter (MPa) Grain 

orientation 

Moisture 

content 3.33-mm 4.11-mm 5.76-mm 3.33-mm 4.11-mm 5.76-mm 

Parallel 6% 78.6 71.0 76.4 34.94 32.61 30.91 

 9% 107.6 85.9 60.8 34.51 32.62 30.34 

 12% 80.0 72.7 75.8 28.89 27.68 31.95 

 17% 60.6 52.5 54.9 23.66 22.54 18.42 

 Saturated 27.2 22.5 9.4 16.10 15.59 14.35 

Perpendicular 6% 36.6 28.1 25.5 23.70 22.68 22.39 

 9% 37.2 30.6 23.2 24.33 22.45 20.44 

 12% 32.0 25.3 21.2 21.61 20.45 18.82 

 17% 19.7 17.2 13.2 17.51 16.19 13.13 

 Saturated 7.2 5.6 4.3 11.21 8.71 6.95 
15 

Table 9—Equations fit to stiffness and moisture content levels to determine Mp

P = A(MC)2

 + B(MC) + C (N/mm3)

a 

Species 

Grain 

orientation 

Nail 

diameter 

(mm) A B C r

2 

Moisture 

intersection 

Mp

Yellow-cedar Parallel 4.11 99.2 1,341.6 −7,324.1 0.73 22.1 

 Perpendicular 4.11 76.0 −289.9 — 0.60 22.5 

Maple Parallel 4.11 459.2 −3,459.4 7,577.2 0.77 21.6 

 Perpendicular 4.11 142.5 −450.9 — 0.66 27.4 

Southern Pine Parallel 4.11 121.8 −40.17 −910.2 0.40 28.4 

 Perpendicular 4.11 48.7 186.1 −1,928.7 0.83 19.7 

Spruce–Pine–Fir Parallel 3.33 61.8 667.2 −3,886.0 0.48 21.3 

 Perpendicular 3.33 49.8 −172.7 — 0.63 24.7 

 Parallel 4.11 64.6 311.4 −2,106.1 0.39 23.3 

 Perpendicular 4.11 38.3 −124.7 — 0.68 26.2 

 Parallel 5.76 70.5 110.1 −1,176.4 0.54 27.9 

 Perpendicular 5.76 32.5 −108.5 — 0.60 25.9 

 Parallel All sizes 67.5 336.6 −2,317.3 0.45 23.3 

 Perpendicular All sizes 40.6 −137.6 — 0.57 25.3 

a

P = 20% to 40% of maximum load nail bearing stiffness (in N/mm3

). 

Table 10—Equations fit to 5% diameter offset dowel bearing strength and moisture content levels to 

determine Mp

P = A(MC)2

 + B(MC) + C (MPa)a 

Species 

Grain 

orientation 

Nail 

diameter 

(mm) A B C r

2 

Moisture 

intersection 

Mp

Yellow-cedar Parallel 4.11 72.31 −232.93 — 0.89 21.3 

 Perpendicular 4.11 43.41 −125.29 — 0.79 23.1 

Maple Parallel 4.11 131.94 −789.79 1,559.60 0.86 21.5 

 Perpendicular 4.11 74.03 −189.48 — 0.81 27.9 

Southern Pine Parallel 4.11 36.31 292.77 −1,755.94 0.61 20.0 

 Perpendicular 4.11 64.10 −218.91 — 0.87 22.0 

Spruce–Pine–Fir Parallel 3.33 42.92 −115.00 — 0.74 23.5 

 Perpendicular 3.33 28.97 −67.47 — 0.75 26.1 

 Parallel 4.11 39.57 −99.29 — 0.55 24.2 

 Perpendicular 4.11 27.23 −65.20 — 0.81 28.4 

 Parallel 5.76 22.69 218.89 −1,390.10 0.65 19.0 

 Perpendicular 5.76 27.91 −85.54 — 0.86 24.4 

 Parallel All sizes 41.20 −110.94 — 0.62 23.4 

 Perpendicular All sizes 29.92 −71.19 — 0.76 26.5 

a

P = 5% diameter offset nail bearing strength (in MPa). 
16 

distributions will need to be quantified. Since the SP and SPF 

grouping had a minimum of 37 specimens, an analysis of 

both the 5% diameter offset strength distributions was warranted. Maximum likelihood estimators examined three types 

of distributions: normal, lognormal, and two-parameter 

Weibull. These distributions were chosen because they are 

typically used to classify mechanical response in wood and 

wood-based materials. Chi-squared (χ2

), Anderson–Darling 

(A–D), and Kolmogorov–Smirnov (K–S) tests were performed to evaluate the goodness of fit of these distributions 

to the data. All distribution parameters found by the likelihood estimators along with the goodness of fit estimates are 

listed in Table 11 for parallel-to-grain results and Table 12 

for perpendicular-to-grain results. Based on goodness of fit 

comparisons, the best-fit distribution for each size nail is 

shown by the footnote in Tables 11 and 12. For parallel-tograin bearing strength, the normal distribution best-fit 13 of 

the 19 combinations, and for the perpendicular-to-grain 

bearing strength, no distribution predominantly fit the data. 

Specific Gravity–Nail Bearing 

Strength Relationship 

For clear wood mechanical properties, there is typically a 

strong correlation to specific gravity. This is also true for 

both dowel bearing stiffness and strength (Wilkinson 1991, 

Koponen 1991, Smith and others 1988). Linear relationships 

were developed at 6%, 12%, 15%, and saturated moisture 

conditions for the 4.11-mm nail diameter data. Moisture 

conditions represented extreme conditions (6% and saturated), typical testing conditions (12%), and the design standard for dry lumber (15%). 

Prior to regression analysis, both nail stiffness and bearing 

strength results were adjusted to the four moisture conditions, 

6%, 12%, 15%, and saturated, using expressions listed in 

Tables 9 and 10. Linear regressions were developed at each 

of the four moisture levels for parallel to grain, perpendicular 

to grain, and a combined set considering both orientations. 

Linear expressions relating specific gravity and nail bearing 

stiffness, r

2

, mean deviation, and standard error are listed in 

Table 13. These linear type expressions fit the perpendicularto-grain results best. For the other two sets, parallel to grain 

and combined, the r

2

 values indicate a weak to no linear 

correlation between specific gravity and nail bearing stiffness. Linear expressions relating specific gravity and nail 

bearing strength, r

2

, mean deviation, and standard error are 

listed in Table 14. Linear expression fit all parallel, perpendicular, and combined data well. As with the stiffness results, 

linear expression tends to fit perpendicular-to-grain better 

than the other sets. Tables 13 and 14 indicate that the effect 

of specific gravity decreases as the MC approaches a saturated condition and that specific gravity is positively correlated with both nail bearing stiffness and strength. 

To investigate if Wilkinson’s specific gravity–nail bearing 

relationship was affected by the lower MC specimens, it was 

compared with a relationship developed in the study. 

Figure 12 compares bearing strengths of both the experimental parallel (solid symbols) and perpendicular (open symbols) 

to grain results with specific gravity. The results in Figure 12 

are experimental bearing strengths from 4.11-mm-diameter 

nails adjusted to 12% MC by expressions in Table 10. Also 

compared are the equations by Wilkinson and from Table 14 

for 12% MC using the combined data. Across the entire 

specific gravity range, parallel-to-grain strengths are higher 

than the perpendicular-to-grain values as confirmed by a 

statistical comparison for each species. The fitted expression 

predicts the middle response of the data, as determined by a 

residual analysis, with a range of percentage deviation (PD) 

of the fitted expression and experimental values of 88.3% to 

−51.9% with an average PD of −0.02. For Wilkinson’s expression, the range of PD was 81.6% to −52.7% with an 

average of −0.73. Based on PD and an analysis of the actual 

residuals, Wilkinson’s expression overpredicts nail bearing 

strengths for higher specific gravity values. Percentage difference between Wilkinson’s expression and the 12% MC 

combined expression in Table 14 as it varies with specific 

gravity is also shown in Figure 12. At a specific gravity of 

0.48, both expressions are equivalent, but for values lower 

than 0.39 and higher than 0.6, the expressions differ by 

greater than 10%. For typical wood species used in construction, the difference between the best-fit and Wilkinson’s is 

less than 10%. 

Figure 12—Nail bearing versus specific gravity for 

4.11-mm nails at 12% MC (Filled symbols are parallelto-grain strengths, open symbols are perpendicularto-grain strengths). 
17 

Table 11—Parallel-to-grain 5% diameter offset strength probability distributions 

Species 

Nail 

diameter 

Moisture 

content Distributiona

 Scale (α) Shape(β) χ2 K-S A-D 

Southern Pine 4.11 6% Normalb 47.01 165.78 5.945 0.1063 0.4425 

 Lognormal 3.809 0.08732 5.946 0.1546 0.5958 

 Weibull 51.86 4.180 6.324 0.1009 0.4205 

 9% Normab

 49.32 83.30 4.432 0.0867 0.2976 

 Lognormal 3.881 0.03500 4.432 0.0971 0.3902 

 Weibull 53.14 5.701 7.459 0.0771 0.3624 

 12% Normal 45.52 79.50 4.814 0.1100 0.6433 

 Lognormalb 3.799 0.03863 5.930 0.0946 0.4182 

 Weibull 49.23 5.481 10.767 0.1335 0.8715 

 17% Normalb

 35.58 36.97 2.162 0.0808 0.2619 

 Lognormal 3.556 0.03192 5.568 0.1163 0.5470 

 Weibull 38.12 6.624 2.919 0.1029 0.2169 

 Saturated Normalb

 24.50 15.79 3.676 0.1010 0.2952 

 Lognormal 3.185 0.02918 1.027 0.1176 0.3882 

 Weibull 26.17 7.104 4.432 0.1065 0.3244 

Spruce–Pine–Fir 3.33 6% Normalb

 35.21 61.76 5.600 0.0597 0.1488 

 Lognormal 3.535 0.05327 4.000 0.0970 0.3182 

 Weibull 38.33 4.763 2.800 0.0742 0.2843 

 9% Normalb

 34.36 70.60 4.000 0.0702 0.3377 

 Lognormal 3.503 0.07608 6.400 0.1189 0.6806 

 Weibull 37.56 4.533 4.800 0.0863 0.4938 

 12% Normalb

 28.02 33.97 8.122 0.0630 0.1751 

 Lognormal 3.310 0.04845 7.755 0.0879 0.4046 

 Weibull 30.38 5.470 2.612 0.0729 0.1969 

 17% Normalb

 23.30 17.25 3.347 0.0614 0.2655 

 Lognormal 3.132 0.03381 3.347 0.0804 0.3630 

 Weibull 25.04 6.306 2.612 0.0730 0.3248 

 Saturated Normalb

 16.10 16.28 7.755 0.1240 0.5421 

 Lognormal 2.746 0.06712 3.347 0.0771 0.3483 

 Weibull 17.66 4.310 9.224 0.1386 0.7149 

Spruce–Pine–Fir 4.11 6% Normalb

 33.04 96.14 18.408 0.1192 0.5031 

 Lognormal 3.441 0.13850 16.939 0.1710 1.7811 

 Weibull 36.50 3.705 16.939 0.1255 0.6268 

 9% Normal 32.38 73.73 1.875 0.0972 0.4371 

 Lognormalb 3.444 0.06746 4.125 0.0733 0.2986 

 Weibull 35.63 3.727 6.750 0.1208 0.9152 

 12% Normal 26.88 56.48 8.250 0.1076 0.4402 

 Lognormal 3.244 0.10820 14.250 0.1707 1.486 

 Weibullb

 29.62 4.100 10.125 0.0975 0.3734 

 17% Normalb

 22.11 24.38 7.600 0.0982 0.5497 

 Lognormal 3.068 0.05960 10.00 0.1455 1.205 

 Weibull 24.04 4.726 7.200 0.1028 0.7689 

 Saturated Normal 15.59 20.09 5.600 0.0826 0.6376 

 Lognormalb 2.708 0.07719 3.600 0.0729 0.2434 

 Weibull 17.25 3.485 8.400 0.1064 0.9713 

Spruce–Pine–Fir 5.76 6% Normal 30.67 86.29 8.205 0.1128 0.5229 

 Lognormalb 3.376 0.09688 3.538 0.0781 0.2966 

 Weibull 34.06 3.603 6.769 0.1196 0.4927 

 9% Normal 30.43 48.13 4.894 0.0951 0.3193 

 Lognormalb 3.389 0.05429 7.957 0.0753 0.3063 

 Weibull 33.19 4.792 8.723 0.1108 0.3647 

 12% Normal 31.49 39.74 7.191 0.1192 0.6007 

 Lognormal 3.429 0.04117 13.702 0.0834 0.3845 

 Weibull 34.10 5.304 12.553 0.8741 0.1446 

 17% Normalb

 17.42 27.63 6.043 0.0881 0.4222 

 Lognormal 2.800 0.13473 17.532 0.1658 1.6929 

 Weibullb

 19.28 3.764 6.043 0.0885 0.4077 

 Saturated Normalb

 14.35 9.957 5.277 0.0957 0.3797 

 Lognormal 2.638 0.05223 7.957 0.0848 0.4596 

 Weibull 15.61 5.000 6.043 0.1084 0.4665 

a

Normal: 















 − −

= β

α

πβ

2

2 ( )

2

1 ( )

x

x f x e Lognormal: 















 − −

= β

α

πβ

2

2 (ln )

2

1 ( )

x

x e x f x Weibull: α α β

α β

α 1 ( ) ( ) − − [ f x = x e x

b

Best-fitting curve for bearing strength. 
18 

Table 12—Perpendicular-to-grain 5% diameter offset strength probability distributions

Species 

Nail 

diameter 

Moisture 

content Distributiona

 Scale (α) Shape (β) χ2 K-S A-D 

Southern Pine 4.11 6% Normal 50.35 96.40 3.297 0.0869 0.3240 

 Lognormalb 3.900 0.03882 2.162 0.0869 0.2689 

 Weibull 54.44 5.623 4.811 0.0858 0.3950 

 9% Normal 46.67 55.00 12.000 0.1804 1.1520 

 Lognormalb 3.831 0.02259 8.595 0.1564 0.7348 

 Weibull 49.95 5.999 16.919 0.1858 1.6414 

 12% Normal 37.36 45.44 5.238 0.1038 0.4989 

 Lognormalb 3.605 0.03221 1.048 0.1109 0.2951 

 Weibull 40.23 5.930 8.286 0.1128 0.6817 

 17% Normalb

 26.05 26.98 2.846 0.1181 0.2797 

 Lognormal 3.239 0.04289 1.692 0.1446 0.4032 

 Weibull 28.18 5.589 2.846 0.1454 0.2901 

 Saturated Normal 15.83 8.882 4.054 0.1232 0.4489 

 Lognormalb 2.744 0.03479 5.189 0.0861 0.2294 

 Weibull 17.09 5.493 5.568 0.1443 0.7740 

Spruce–Pine–Fir 3.33 6% Normal 24.21 57.75 8.122 0.0929 0.5164 

 Lognormal 3.138 0.09886 17.673 0.1088 0.4578 

 Weibull 26.94 3.323 14.735 0.0875 0.6077 

 9% Normalb

 24.30 51.75 1.600 0.0692 0.2261 

 Lognormal 3.145 0.09466 7.600 0.0746 0.3280 

 Weibull 26.92 3.575 5.600 0.0667 0.3240 

 12% Normal 21.12 35.44 14.625 0.0974 0.3576 

 Lognormal 3.008 0.08916 14.250 0.1176 0.5431 

 Weibullb

 23.33 3.830 13.500 0.0822 0.3790 

 17% Normalb

 17.15 20.55 6.375 0.0827 0.4196 

 Lognormal 2.806 0.07583 7.875 0.1214 0.7516 

 Weibull 18.85 3.867 6.375 0.1019 0.6838 

 Saturated Normal 11.21 11.30 7.875 0.1405 1.2274 

 Lognormalb 2.374 0.08317 4.875 0.1216 0.6155 

 Weibull 12.45 3.497 13.125 0.1330 1.1713 

Spruce–Pine–Fir 4.11 6% Normal 22.80 47.50 4.082 0.1136 0.7121 

 Lognormalb 3.082 0.09120 14.000 0.0971 0.6670 

 Weibull 25.28 3.365 8.491 0.1310 1.0178 

 9% Normalb

 22.37 38.54 11.061 0.0850 0.4120 

 Lognormal 3.067 0.08587 11.796 0.1305 0.6635 

 Weibull 24.70 3.916 11.429 0.0988 0.4722 

 12% Normal 19.89 32.10 8.857 0.0691 0.4405 

 Lognormal 2.949 0.08360 8.490 0.0780 0.3944 

 Weibull 21.98 3.693 5.184 0.0843 0.5709 

 17% Normalb

 15.97 18.50 3.714 0.0709 0.2387 

 Lognormal 2.732 0.08322 8.857 0.1276 0.6017 

 Weibull 17.60 4.096 4.816 0.0759 0.2657 

 Saturated Normal 8.70 7.658 14.735 0.1204 0.7919 

 Lognormal 2.116 0.09326 9.224 0.1163 0.4080 

 Weibullb

 9.69 3.245 8.490 0.0941 0.8064 

Spruce–Pine–Fir 5.76 6% Normalb

 22.74 31.41 3.273 0.0689 0.2983 

 Lognormal 3.093 0.06319 8.364 0.0932 0.3585 

 Weibull 24.92 4.350 8.000 0.0810 0.3798 

 9% Normalb

 20.55 27.46 3.745 0.0931 0.2566 

 Lognormal 2.990 0.06876 6.043 0.1006 0.3897 

 Weibull 22.57 4.237 4.128 0.0914 0.2813 

 12% Normal 18.11 17.79 3.200 0.0882 0.2907 

 Lognormal 2.866 0.06345 8.800 0.1324 0.7334 

 Weibullb

 19.75 4.957 1.600 0.0688 0.2120 

 17% Normal 12.77 10.62 3.696 0.0764 0.1945 

 Lognormal 2.511 0.07904 10.739 0.1271 0.6133 

 Weibullb

 14.02 4.491 2.913 0.0791 0.1595 

 Saturated Normal 6.95 3.60 6.435 0.0932 0.5898 

 Lognormalb 1.902 0.07105 2.522 0.0673 0.1943 

 Weibull 7.67 3.816 7.217 0.0910 0.7162 

a

Normal: 















 − −

= β

α

πβ

2

2 ( )

2

1 ( )

x

x f x e Lognormal: 















 − −

= β

α

πβ

2

2 (ln )

2

1 ( )

x

x e x f x Weibull: α α β

α β

α 1 ( ) ( ) − − [ f x = x e x

b

Best-fitting curve for bearing strength. 
19 

Conclusions 

Based on the results of this study on the effect of MC on the 

nail bearing properties in yellow-cedar, maple, Southern 

Pine, and Spruce–Pine–Fir, the following can be concluded: 

• Parallel-to-grain offset loads increased 7.7% from the 

reference 5% offset values to the 50% offset load values. 

Perpendicular-to-grain offset loads significantly increased 

from the reference 5% values, with a nearly 28.5% increase to a 50% offset load. 

• Grain orientation significantly affected both the nail 

bearing stiffness and strength. 

• ANOVA results did not conclusively determine that all nail 

diameters had a significant effect on bearing strength, but 

average values decreased as the nail diameter increased. 

• MC was negatively correlated with nail stiffness and bearing strength. Expressions relating MC to nail stiffness and 

bearing strength for each wood species were developed. 

Table 13— Linear regression relationship between specific gravity and nail bearing stiffness 

P = A + B(G)a 

Grain 

orientation 

Moisture 

content A B r

2 Mean 

deviation 

Standard 

error 

Parallel 6% −150.53 543.15 0.52 3.97 49.40 

 12% 18.58 170.43 0.17 −0.33 41.06 

 15% −10.95 207.85 0.33 −0.73 36.82 

 Saturated −8.55 80.97 0.30 −0.12 39.99 

Perpendicular 6% −72.20 240.08 0.58 31.03 380.11 

 12% −49.53 176.29 0.59 3.71 42.69 

 15% −41.10 142.55 0.54 7.15 56.53 

 Saturated −10.17 38.30 0.54 2.54 37.05 

Combined 6% −107.55 386.83 0.32 4.08 70.43 

 12% −13.77 171.79 0.16 −0.58 62.80 

 15% −24.43 177.32 0.20 −1.02 63.11 

 Saturated −8.14 58.28 0.14 −0.24 70.78 

a

P = 20% to 40% of maximum load nail bearing stiffness (in N/mm3

). 

Table 14—Linear regression relationship between specific gravity and nail bearing strength

P = A + B(G)a 

Grain 

orientation 

Moisture 

content A B r

2 Mean 

deviation 

Standard 

error 

Parallel 6% −30.48 155.99 0.57 0.78 27.71 

 12% −13.68 101.86 0.75 −0.19 17.84 

 15% −13.71 94.25 0.84 −0.03 13.89 

 Saturated −6.63 54.24 0.72 −0.12 17.58 

Perpendicular 6% −36.92 142.95 0.89 1.78 19.34 

 12% −24.38 105.48 0.87 0.76 15.35 

 15% −20.62 90.02 0.84 1.18 16.58 

 Saturated −8.63 42.32 0.69 −0.08 21.85 

Combined 6% −33.00 148.61 0.61 0.83 30.40 

 12% −18.82 103.50 0.73 −0.02 22.13 

 15% −16.93 92.40 0.74 0.12 21.57 

 Saturated −7.22 47.84 0.49 −0.24 30.82 

a

P = 5% diameter offset nail bearing strength (in MPa). 
20 

• A normal distribution fit the probability distribution of 

parallel-to-grain nail bearing strength but no distribution 

adequately fit the perpendicular-to-grain nail bearing 

strength. 

• Both nail bearing stiffness and strength were positively 

correlated to specific gravity. However, the slope of the 

specific gravity–nail bearing strength relationship was a 

function of MC. 

• Linear expressions relating specific gravity and nail 

bearing strength were developed at 6%, 12%, 15%, and 

saturated moisture conditions. 

• For typical wood species used in construction, the difference between the best-fit linear expression for 12% MC, 

4.11-mm experimental nail bearing strength compared with 

specific gravity and Wilkinson’s is less than 10%. 

References 

AF&PA. 1997. National design specification for wood 

construction. Washington, DC: American Forest & Paper 

Association. 

ASCE. 1996. Load and resistance factored design for engineered wood construction. Reston, VA: American Society 

of Civil Engineers. 

ASTM. 1995a. Standard test methods for specific gravity 

of wood and wood-base materials. ASTM D2395–93. West 

Conshohocken, PA: American Society for Testing and 

Materials. 

ASTM. 1995b. Standard test methods for direct moisture 

content measurement of wood and wood-base materials. 

ASTM D4442–92. West Conshohocken, PA: American 

Society for Testing and Materials. 

ASTM. 1996. Standard test method for evaluating dowelbearing strength of wood and wood-base materials. ASTM 

D5764–95. West Conshohocken, PA: American Society for 

Testing and Materials. 

European Committee for Standardization. 1993. Timber 

structures—Test methods—Determination of embedding 

strength and foundation values for dowel type fasteners. 

European Standard EN 383. Brussels, Belgium: European 

Committee for Standardization. 

Fahlbusch, H. 1949. A contribution to the problem of the 

bearing strength of bolts in wood under static loads. 

Rep. 49–09, Institute for Mechanical Construction and 

Carpentry, Technical School Braunschweig. Trans. 218 from 

German. Madison, WI: U.S. Department of Agriculture, 

Forest Service, Forest Products Laboratory. 

Forest Products Laboratory. 1999. The wood handbook: 

wood as an engineering material. Gen. Tech. Rep. 

FPL–GTR–113. Madison, WI: U.S. Department of Agriculture Forest Service, Forest Products Laboratory. 463 p. 

Green, D.W.; Kretschmann, D.E. 1994. Moisture content 

and the properties of clear Southern Pine. Res. Pap. 

FPL–RP–531. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

Koponen, S. 1991. Embedding characteristics of wood in the 

grain direction. Rep. 25. Espoo, Finland: Helsinki University 

of Technology, Laboratory of Structural Engineering and 

Building Physics. 21 p. 

Pope, D.J.; Hilson, B.O. 1995. Embedment testing for bolts: 

A comparison of the European and American procedures. 

Journal of the Institute of Wood Science. 13(6): 568–571 

(Issue 78). 

Rammer, D.R. 1999. Parallel-to-grain dowel-bearing 

strength of two Guatemalan hardwoods. Forest Products 

Journal. 49(6): 77–87. 

Rammer, D.R.; Winistorfer, S.G. 2001. Effect of moisture 

content on dowel-bearing strength. Wood and Fiber Science. 

33(1): 126–139. 

Smith, I.; Whale, R.J.; Anderson, C.; Hilson, B.O.; Rodd, 

P.D. 1988. Design properties of laterally loaded nailed and 

bolted wood joints. Canadian Journal of Civil Engineering. 

15: 633–643. 

Wilkinson, T.L. 1991. Dowel bearing strength. Res. Pap. 

FPL–RP–505. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 

Wilson, T.R.C. 1932. Strength–moisture relations for wood. 

Tech. Bull. 282. Washington, DC: U.S. Department of 

Agriculture. 

Winistorfer, S.G. 1994. Validation of the European yield 

model for nailed connections. In: Proceedings of structures 

congress 1994; 1994 April 24–28; Atlanta, GA. New York: 

American Society of Civil Engineers. 
21 

Appendix—Nonparametric Distributional Information 

Table A1—Nonparametric distributional information for 5% diameter offset bearing strength—parallel to grain

 Bearing strength 

Moisture Percentiles (MPa) 

content 

Sample 

size 

Mean 

 (MPa) 

COV 

(%) 

Min. 

(MPa) 10th 25th 50th 75th 90th 

Max. 

(MPa) 

Yellow-cedar

6% 33 56.84 15.6 36.10 42.65 52.23 58.37 62.78 64.69 75.39 

12% 34 42.38 15.4 17.88 36.10 39.60 42.60 46.76 49.25 56.17 

17% 34 31.01 14.5 17.14 24.73 28.72 30.85 33.88 35.64 41.81 

Saturated 34 23.21 19.1 17.80 18.57 20.20 22.10 24.87 31.67 34.71 

 

Maple

6% 30 79.67 16.3 54.08 59.88 71.89 81.59 89.31 96.20 106.53 

12% 30 48.09 16.4 29.00 38.56 43.29 47.21 54.12 60.02 64.41 

17% 30 44.76 16.9 30.59 32.88 39.91 44.94 48.46 52.92 62.69 

Saturated 31 31.02 14.7 23.08 24.55 27.14 31.23 34.39 36.94 41.77 

 

Southern Pine

6% 37 47.20 27.6 22.19 28.37 36.89 49.93 57.20 65.63 68.74 

9% 37 49.22 18.8 33.20 38.02 41.11 49.75 56.15 61.02 74.34 

12% 43 46.59 19.4 29.73 35.63 40.91 44.96 52.33 60.56 66.37 

17% 37 34.31 16.7 24.46 27.26 29.17 32.99 38.70 41.59 48.86 

Saturated 37 24.50 16.5 14.36 19.74 21.76 24.34 27.88 29.73 32.38 

 

Spruce–Pine–Fir: 3.33 mm

6% 45 34.94 22.3 19.57 24.89 29.07 35.08 40.47 44.64 57.78 

9% 50 34.51 24.2 11.06 23.92 29.33 33.99 39.14 48.68 52.26 

12% 49 28.89 19.4 16.78 21.29 25.02 28.65 32.87 36.64 41.17 

17% 49 23.66 17.4 14.00 19.04 20.85 23.14 25.25 31.33 31.69 

Saturated 49 16.10 25.3 7.72 10.57 13.24 15.67 18.74 23.28 24.51 

 

Spruce–Pine–Fir: 3.76 mm

12% 31 29.66 24.2 16.73 22.99 24.89 28.30 32.99 36.97 56.95 

 

Spruce–Pine–Fir: 4.11 mm

6% 49 32.61 30.2 7.63 20.25 27.26 33.02 36.26 44.29 54.02 

9% 48 32.62 26.5 16.03 21.63 27.16 33.08 36.69 42.17 66.10 

12% 49 27.68 26.0 11.25 17.36 23.25 28.13 32.73 36.30 47.29 

17% 50 22.54 22.0 12.49 16.44 19.22 22.09 25.27 28.59 38.17 

19% 50 22.30 20.7 13.17 14.93 19.01 22.62 25.11 29.13 32.83 

Saturated 50 15.59 29.0 7.10 10.59 12.10 15.16 18.13 20.20 32.13 

 

Spruce–Pine–Fir: 5.76 mm

6% 39 30.91 30.7 15.28 19.10 22.96 29.85 38.99 45.73 50.59 

9% 47 30.34 23.0 17.44 21.23 24.40 29.20 35.23 40.10 46.88 

12% 47 31.95 19.0 19.22 24.77 27.67 30.62 36.68 41.05 47.32 

17% 47 18.42 21.2 8.19 13.18 15.39 18.59 21.70 23.71 25.84 

Saturated 47 14.35 22.2 8.14 9.26 12.39 13.67 17.09 18.36 21.44 
22 

Table A2—Nonparametric distributional information for 5% diameter offset bearing strength—perpendicular to grain

 Bearing strength 

Moisture Percentiles (MPa) 

content 

Sample 

size 

Mean 

 (MPa) 

COV 

(%) 

Min. 

(MPa) 10th 25th 50th 75th 90th 

Max. 

(MPa) 

Yellow-cedar

6% 24 35.55 15.88 24.89 27.48 31.09 35.46 39.92 43.97 45.57 

12% 26 27.62 23.25 17.37 18.28 21.82 27.71 31.76 36.87 40.55 

17% 23 21.03 17.67 14.46 15.00 18.40 21.09 23.58 25.36 29.71 

Saturated 24 14.49 27.7 8.61 10.13 11.28 13.50 17.62 21.52 23.59 

 

Maple

6% 29 60.08 19.0 39.02 42.54 49.42 60.79 69.26 75.24 81.38 

12% 30 46.99 20.4 29.69 35.35 39.90 46.57 53.69 59.82 73.36 

17% 29 39.43 20.0 25.06 30.74 33.04 38.73 45.03 50.17 57.39 

Saturated 30 21.29 26.5 11.46 13.58 17.94 19.69 24.31 31.13 32.63 

 

Southern Pine

6% 37 49.90 19.9 32.81 36.67 40.94 49.36 57.98 63.43 70.79 

9% 37 45.36 16.9 34.29 37.39 39.53 43.03 50.21 57.89 68.28 

12% 42 40.08 17.0 27.42 32.04 35.51 38.81 45.30 51.02 53.68 

17% 37 26.39 17.0 19.36 21.21 23.93 24.61 28.94 33.53 37.27 

Saturated 37 15.30 19.1 10.50 12.08 13.78 15.84 17.83 20.71 22.88 

 

Spruce–Pine–Fir: 3.33 mm

6% 49 23.70 34.6 11.10 15.01 17.30 23.69 29.09 32.80 48.10 

9% 48 24.33 29.6 10.63 15.28 19.00 23.58 28.46 32.95 46.30 

12% 48 21.61 26.5 9.94 15.49 16.79 21.60 25.25 28.68 38.54 

17% 48 17.51 25.9 8.74 12.31 14.60 17.09 20.13 23.13 35.14 

Saturated 48 11.21 30.3 6.56 8.07 8.58 10.41 13.50 16.20 20.61 

 

Spruce–Pine–Fir: 3.76 mm

12% 46 20.80 22.4 11.73 14.68 18.40 20.13 23.35 27.65 32.60 

 

Spruce–Pine–Fir: 4.11 mm

6% 49 22.68 30.6 10.77 14.57 17.88 22.85 26.17 29.04 46.04 

9% 49 22.45 27.5 11.13 14.56 17.68 23.37 24.98 32.05 37.14 

12% 49 20.45 26.8 10.62 14.25 16.09 20.29 23.97 25.81 35.48 

15% 50 16.19 26.5 9.02 9.05 13.34 15.52 18.14 23.57 27.65 

17% 50 15.51 24.3 8.38 10.24 13.20 15.30 17.84 19.91 25.09 

Saturated 49 8.71 32.1 4.49 5.68 6.37 8.22 10.57 12.44 18.38 

 

Spruce–Pine–Fir: 5.76 mm

6% 44 22.39 24.7 12.59 15.16 17.97 21.76 25.96 29.81 36.46 

9% 47 20.44 25.6 11.73 13.70 16.49 21.24 23.73 27.30 34.49 

12% 46 18.82 21.3 10.93 13.19 15.57 18.72 22.04 24.25 26.77 

17% 46 13.13 21.4 8.56 9.30 10.96 12.25 15.12 17.26 19.58 

Saturated 46 6.95 27.6 3.90 4.87 5.43 6.59 8.02 9.50 11.83