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Wood Strengths

The table below provides laboratory values for several properties of wood that are associated with wood strength. Note that due to inadequacies of samples, these values may not necessarily represent average characteristics .

 

Tree Species Average Specific Gravity, Oven Dry  Sample Static Bending Modulus of Elasticity (E) Impact Bending, Height of Drop Causing Failure Compress. Parallel to Grain, Max Crushing Strength Compress. Perpen.  to Grain, Fiber Stress at Prop. Limit Shear Parallel to Grain, Max Shear Strength

(0-1.0) 10^6 psi inches psi psi psi
U. S. Hardwoods
Alder, Red 0.41 1.38 20 5,820 440 1,080
Ash, Black 0.49 1.60 35 5,970 760 1,570
Ash, Blue 0.58 1.40 - 6,980 1,420 2,030
Ash, Green 0.56 1.66 32 7,080 1,310 1,910
Ash, Oregon 0.55 1.36 33 6,040 1,250 1,790
Ash, White 0.60 1.74 43 7,410 1,160 1,910
Aspen, Bigtooth 0.39 1.43 - 5,300 450 1,080
Aspen, Quaking 0.38 1.18 21 4,250 370 850
Basswood 0.37 1.46 16 4,730 370 990
Beech, American 0.64 1.72 41 7,300 1,010 2,010
Birch, Paper 0.55 1.59 34 5,690 600 1,210
Birch, Sweet 0.65 2.17 47 8,540 1,080 2,240
Birch, Yellow 0.62 2.01 55 8,170 970 1,880
Butternut 0.38 1.18 24 5,110 460 1,170
Cherry, Black 0.50 1.49 29 7,110 690 1,700
Chestnut, American 0.43 1.23 19 5,320 620 1,080
Cottonwood, Balsam Poplar 0.34 1.1 - 4,020 300 790
Cottonwood, Black 0.35 1.27 22 4,500 300 1,040
Elm, Eastern 0.40 1.37 20 4,910 380 930
Elm, American 0.50 1.34 39 5,520 690 1,510
Elm, Rock 0.63 1.54 56 7,050 1,230 1,920
Elm, Slippery 0.53 1.49 45 6,360 820 1,630
Hackberry 0.53 1.19 43 5,440 890 1,590
Hickory, Bitternut 0.66 1.79 66 9,040 1,680 -
Hickory, Nutmeg 0.6 1.70 - 6,910 1,570 -
Hickory, Pecan 0.66 1.73 44 7,850 1,720 2,080
Hickory, Water 0.62 2.02 53 8,600 1,550 -
Hickory, Mockernut 0.72 2.22 77 8,940 1,730 1,740
Hickory, Pignut 0.75 2.26 74 9,190 1,980 2,150
Hickory, Shagbark 0.72 2.16 67 9,210 1,760 2,430
Hickory, Shellbark 0.69 1.89 88 8,000 1,800 2,110
Honeylocust - 1.63 47 7,500 1,840 2,250
Locust, Black 0.69 2.05 57 10,180 1,830 2,480
Magnolia,Cucumbertree 0.48 1.82 35 6,310 570 1,340
Magnolia, Southern 0.50 1.40 29 5,460 860 1,530
Maple, Bigleaf 0.48 1.45 28 5,950 750 1,730
Maple, Black 0.57 1.62 40 6,680 1,020 1,820
Maple, Red 0.54 1.64 32 6,540 1,000 1,850
Maple, Silver 0.47 1.14 25 5,220 740 1,480
Maple, Sugar 0.63 1.83 39 7,830 1,470 2,330
Oak, Black 0.61 1.64 41 6,520 930 1,910
Oak, Cherrybark 0.68 2.28 49 8,740 1,250 2,000
Oak, Laurel 0.63 1.69 39 6,980 1,060 1,830
Oak, Northern Red 0.63 1.82 43 6,760 1,010 1,780
Oak, Pin 0.63 1.73 45 6,820 1,020 2,080
Oak, Scarlet 0.67 1.91 53 8,330 1,120 1,890
Oak, Southern Red 0.59 1.49 26 6,090 870 1,390
Oak, Water 0.63 2.02 44 6,770 1,020 2,020
Oak, Willow 0.69 1.90 42 7,040 1,130 1,650
Oak, Bur 0.64 1.03 29 6,060 1,200 1,820
Oak, Chestnut 0.66 1.59 40 6,830 840 1,490
Oak, Live 0.88 1.98 - 8,900 2,840 2,660
Oak, Overcup 0.63 1.42 38 6,200 810 2,000
Oak, Post 0.67 1.51 46 6,600 1,430 1,840
Oak, Swamp Chestnut 0.67 1.77 41 7,270 1,110 1,990
Oak, Swamp White 0.72 2.05 49 8,600 1,190 2,000
Oak, White 0.68 1.78 37 7,440 1,070 2,000
Sassafras 0.46 1.12 - 4,760 850 1,240
Sweetgum 0.52 1.64 32 6,320 620 1,600
Sycamore, American 0.49 1.42 26 5,380 700 1,470
Tupelo, Black 0.50 1.20 22 5,520 930 1,340
Tupelo, Water 0.50 1.26 23 5,920 870 1,590
Walnut, Black 0.55 1.68 34 7,580 1,010 1,370
Willow, Black 0.39 1.01 - 4,100 430 1,250
Yellow-poplar 0.42 1.58 24 5,540 500 1,190
U. S. Softwoods
Baldcypress 0.46 1.44 24 6,360 730 1,000
Cedar, Alaska 0.44 1.42 29 6,310 620 1,130
Cedar, Atlantic White 0.32 0.93 13 4,700 410 800
Cedar, Eastern Redcedar 0.47 0.88 22 6,020 920 -
Cedar, Incense 0.37 1.04 17 5,200 590 880
Cedar, Northern White 0.31 0.80 12 3,960 310 850
Cedar, Port-Orford 0.43 1.70 28 6,250 720 1,370
Cedar, Western Redcedar 0.32 1.11 17 4,560 460 990
Douglas-fir, Coast 0.48 1.95 31 7,230 800 1,130
Douglas-fir, Interior West 0.50 1.83 32 7,430 760 1,290
Douglas-fir, Interior North 0.48 1.79 26 6,900 770 1,400
Douglas-fir, Interior South 0.46 1.49 20 6,230 740 1,510
Fir, Balsam 0.35 1.45 20 5,280 404 944
Fir, California Red 0.38 1.50 24 5,460 610 1,040
Fir, Grand 0.37 1.57 28 5,290 500 900
Fir, Noble 0.39 1.72 23 6,100 520 1,050
Fir, Pacific silver 0.43 1.76 24 6,410 450 1,220
Fir, Subalpine 0.32 1.29 - 4,860 390 1,070
Fir, White 0.39 1.50 20 5,800 530 1,100
Hemlock, Eastern 0.40 1.20 21 5,410 650 1,060
Hemlock, Mountain 0.45 1.33 32 6,440 860 1,540
Hemlock, Western 0.45 1.63 23 7,200 550 1,290
Larch, western 0.52 1.87 35 7,620 930 1,360
Pine, Eastern white 0.35 1.24 18 4,800 440 900
Pine, Jack 0.43 1.35 27 5,660 580 1,170
Pine, Loblolly 0.51 1.79 30 7,130 790 1,390
Pine, Lodgepole 0.41 1.34 20 5,370 610 880
Pine, Longleaf 0.59 1.98 34 8,470 960 1,510
Pine, Pitch 0.52 1.43 - 5,940 820 1,360
Pine, Pond 0.56 1.75 - 7,540 910 1,380
Pine, Ponderosa 0.40 1.29 19 5,320 580 1,130
Pine, Red 0.46 1.63 26 6,070 600 1,210
Pine, Sand 0.48 1.41 - 6,920 836 -
Pine, Shortleaf 0.51 1.75 33 7,270 820 1,390
Pine, Slash 0.59 1.98 - 8,140 1,020 1,680
Pine, Spruce 0.44 1.23 - 5,650 730 1,490
Pine, Sugar 0.36 1.19 18 4,460 500 1,130
Pine, Virginia 0.48 1.52 32 6,710 910 1,350
Pine, Western white 0.38 1.46 23 5,040 470 1,040
Redwood, Old-growth 0.40 1.34 19 6,150 700 940
Redwood, Young-growth 0.35 1.10 15 5,220 520 1,110
Spruce, Black 0.42 1.61 23 5,960 550 1,230
Spruce, Engelmann 0.35 1.30 18 4,480 410 1,200
Spruce, Red 0.40 1.61 25 5,540 550 1,290
Spruce, Sitka 0.40 1.57 25 5,610 580 1,150
Spruce, White 0.36 1.43 20 5,180 430 970
Tamarack 0.53 1.64 23 7,160 800 1,280


Strength may be defined as the ability to resist applied stress: the greater the resistance, the stronger the material. Resistance may be measured in several ways. One is the maximum stress that the material can endure before "failure" occurs. Another approach is to measure the deformation or strain that results from a given level of stress before the point of total failure. Strength of wood is often thought of in terms of bending strength. This is certainly a useful yardstick of strength but is by no means the only one. A number of other strength criteria are described below.

Stress
is the amount of force for a given unit of area. It is typically measured in pounds per square inch (psi). Example: if a 1000 pound load was applied on the edge of a block of wood measuring 2-inches by 2-inches in cross-section by 10 inches in length, the applied stress would be 1000 pounds divided by 4 square inches = 250 lb./sq. inch.

Strain
is defined as unit deformation or movement per unit of original length. It is typically expressed in inches per inch. Example: if the 10-inch long block of wood in the stress example above was compressed by 0.002 inches, the strain would be 0.002 inches/10 inches = 0.0002 inches per inch.

Elasticity
is a property of wood in which strains or deformations are recoverable after an applied stress is removed, up to a certain level of stress known as the proportional limit. Below this point, each increment of stress will produce a proportional increment of strain (the stress/strain ratio is constant) and the wood will return to its original position once the stress is removed. Beyond the proportional limit, each increment of stress will cause increasingly larger increments of strain (as failure is approached) and removal of the stress will only result in a partial recovery of the strain.

Modulus of elasticity
or Young's modulus is the ratio of stress to strain. Within the elastic range below the proportional limit, this ratio is a constant for a given piece of wood, making it useful in static bending tests for determining the relative stiffness of a board. The modulus of elasticity is normally measured in pounds per square inch (psi) and is abbreviated as MOE or E. Values for E relating to wood properties are commonly in terms of million psi; for simplicity, a board with a modulus of elasticity of 2,100,000 psi. (2.1 x 106) may be reported as 2.1E.

Modulus of rupture
is the maximum load carrying capacity of a member. It is generally used in tests of bending strength to quantify the stress required to cause failure. It is reported in units of psi.

Fiber stress at proportional limit
represents the maximum stress a board can be subjected to without exceeding the elastic range of the wood. Permanent set will result if an applied stress exceeds the proportional limit. This property is typically reported in units of psi.

Maximum crushing strength
is the maximum stress sustained by a board when pressure is applied parallel to the grain.

Impact bending
involves dropping a hammer of a given weight upon a board from successively greater heights until complete rupture occurs. The height of the drop that causes failure provides a comparative measure of how well the wood absorbs shock. It is reported in units of inches or centimeters.

Stiffness
may be quantified using the modulus of elasticity, E. The higher the E value, the stiffer the wood and the lower the deformation under a given load. A board rated at 2.0E is twice as stiff as one rated at 1.0E.

Compression
stress shortens or compresses the material. For the woodworker, the primary types of compression to consider are parallel to the grain and perpendicular to the grain. Compression parallel to the grain shortens the fibers in the wood lengthwise. An example would be chair or table legs which are primarily subjected to downward, rather than lateral pressure. Wood is very strong in compression parallel to the grain and this is seldom a limiting factor in furniture design. It is considerably weaker in compression perpendicular to the grain. An example of this type of compression would be the pressure that chair legs exert on a wooden floor. If the applied pressure (weight) exceeds the fiber stress at proportional limit for the wood, permanent indentations will result in the floor. Compression stress is measured in psi.

Tensile
stress elongates or expands an object. Measurements of tensile stress perpendicular to the grain are useful for quantifying resistance to splitting. Examples of such stress include splitting firewood, driving nails, and forcing cupped boards to be flat. Wood is relatively weak in tension perpendicular to the grain but it is very strong in tension parallel to the grain (visualize a board being pulled from both ends). Due to difficulties in testing and the limited use for such data, tension parallel to the grain has not been extensively measured and/or reported to date. Tensile stress is measured in psi.

Shear
stress involves the application of stress from two opposite directions causing portions of an object to move in parallel but opposite directions. Wood is very resistant to shearing perpendicular to the grain and this property is not measured via a standard test. Wood shears much easier in a direction parallel to the grain - consider a screw running perpendicular to the grain: it will shear out to the nearest end-grain if a sufficiently large force is applied to the board parallel to the grain. Shear stress is measured in psi.

Density
is weight per unit volume. For wood, density is expressed as pounds per cubic foot, kilograms per cubic meter, or grams per cubic centimeter - at a specified moisture content. Density is the single most important indicator of strength in wood: a wood that is heavier (i.e., more wood substance per unit volume) will generally tend to be stronger than a lighter one.

Specific gravity
as applied to wood, is the ratio of an ovendry weight of a wood sample to the weight of water (whose volume is equal to the volume of the wood sample at a specified moisture content). Specific gravity is often used in place of density to standardize comparisons of wood species - as with density, the higher the specific gravity, the heavier the wood, and the stronger it tends to be. At a moisture content of 12 percent, most woods have a specific gravity between 0.3 to 0.8 (water has a specific gravity of 1.0).

Source: U.S. Forest Products Laboratory and Chris Messier - Messman
 

Need to know more about wood? We recommend the following guides:

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Comments   

 
0 #2 Guest 2013-05-20 18:32
What about Pacific Yew and Osage/Bodock?
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+3 #1 Samuel Markley 2012-03-07 10:12
Thank you very much for this beautifully laid out and insightful work you have done for this page.
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