A. Weight

Wood substance about 1.6 times as heavy as water - depends upon the amount of moisture in the wood substance - sapwood heavier than heartwood - the wood of saplings heavier than the wood of old trees - woods vary in weight from 30 to 40 pounds per cubic foot.

The following table gives the weight of kiln-dried wood of different species: -

Weight Of Kiln-Dried Wood Of Different Species

(Water 62 pounds to cu. ft).

Approximate

Weight of -

Specific Weight

1 cubic foot

1000 feet of lumber

(a) Very heavy woods:

Hickory, oak, persimmon, osage orange, black locust, hackberry, blue beech, best of elm, and ash..........

Pounds

Pounds

0.70-0.80

42-48

3,700

(6) Heavy woods:

Ash, elm, cherry, birch, maple, beech, walnut, sour gum, coffee tree, honey locust, best of Southern pine, and tamarack.....

.60- .70

36-42

3,200

(c) Woods of medium weight:

Southern pine, pitch pine, tamarack, Douglas spruce, Western hemlock, sweet gum, soft maple, sycamore, sassafras, mulberry, light grades of birch and cherry....

.50- .60

30-36

2,700

(d) Light woods:

Norway and bull pine, red cedar, cypress, hemlock, the heavier spruce and fir, redwood, basswood, chestnut, butternut, tulip, catalpa, buckeye, heavier grades of poplar.....

.40- .50

24-30

2,200

(e) Very light woods:

White pine, spruce, fir, white cedar, poplar....

30- .40

18-24

1,800

B. Seasoning

Giving up the moisture that is in the wood.

The following table gives the number of pounds of water lost in drying 100 pounds of green wood in the kiln: -

Pounds Of Water Lost In Drying 100 Pounds Of Green Wood In The Kiln

Sapwood or outer part

Heart wood or interior

(1) Pines, cedars, spruces, and firs............

45-65

16-25

(2) Cypress, extremely variable..........

50-65

18-60

(3) Poplar, cottonwood, basswood.....

60-65

40-60

(4) Oak, beech, ash, elm, maple, birch, hickory, chestnut, walnut, and sycamore............

40-50

30-40

The lighter kinds have the most water in the sap wood, thus sycamore has more than hickory.

C. Shrinkage

The change in size and shape of wood when moisture is given up, causing warping and checking - shrinkage greater in sapwood than in heartwood.

The following table gives the approximate shrinkage of a board, or set of boards, 100" wide, drying in the open air: -

Approximate Shrinkage of a Board, or Set of Boards, 100 " wide,

Drying In The Open Air

Shrinkage

Inches

(1) All light conifers (soft pine, spruce, cedar, cypress)

3

(2) Heavy conifers (hard pine, tamarack, yew), honey locust, box elder, wood of old oaks........

4

(3) Ash, elm, walnut, poplar, maple, beech, sycamore, cherry, black locust.............

5

(4) Basswood, birch, chestnut, horse chestnut, blue beech, young locust.............

6

(5) Hickory, young oak, especially red oak......

Up to 10

D. Stiffness Or Elasticity

The rigidity of a stick of timber which causes it to be bent with difficulty.

Laws

1. Deflection varies directly as the cube of the length.

2. Doubling the width doubles the stiffness.

3. Doubling the thickness increases the stiffness about eightfold.

4. Stiffness varies with the weight (heavier wood being stiffer than light wood).

The modulus (measure) of stiffness of elasticity is determined by the formula -

E (Modulus of elasticity) = Wl3/4Dbd3

W = weight or load; I = length; b = breadth; d = depth; D = deflection.

The number of pounds which will bend a piece of sawed timber by one inch is found by the formula -

Necessary weight = 4Ebd3/l3

Note. - An allowance must be made on the strength of timbers because of the irregularities in the structure of the wood due to knots, cross grain, decay, etc. This allowance is called the "factor of safety." Only about one sixth or one tenth of the strength is considered safe. Timbers in a building are made from 6 to 10 times as heavy as the calculations require. When a stick has been bent beyond its "elastic limit" it still requires an increase of from 30 to 50 per cent to the weight before the stick breaks.

The following table gives the general averages of the stiffness of dry wood: -

Table Of Stiffness (Modulus Of Elasticity) Of Dry Wood. General Averages

Species

Modulus of elasticity

E-Wl3/4Dbd3 per square inch

Approximate weight which deflects by 1 inch a piece -

1 by 1 inch and 12 inches long

2 by 2 inches and 10 feet long

(1) Live oak, good tamarack, longleaf, Cuban, and short-leaf pine, good Douglas spruce, western hemlock, yellow and cherry birch, hard maple, beech, locust, and the best of oak and hickory...........

Pounds

Pounds

Pounds

1,680,000

3,900

62

(2) Birch, common oak, hickory, white and black spruce, loblolly and red pine, cypress, best of ash, elm, and poplar and black walnut.........

1,400.000

3,200

51

(3) Maples, cherry, ash, elm, sycamore, sweet gum, butternut, poplar, basswood, white, sugar and bull pine, cedars, scrub pine, hemlock, and fir....

1,100,000

2,500

40

(4) Box elder, horse chestnut, a number of western soft pines, inferior grades of hard wood..........

1,100,000

12,500

40