* Unit stress producing 10% reduction in original length.

Material.

Ultimate Tensile.

Ultimate Compression.

Ultimate

Shearing.

Modulus of Rupture.

Modulus of

Elasticity.

Millions.

Wrought iron................

50,000

44,000

44,000

48,000

27

Shape iron................

48,000

26

Structural steel..........

60,000

65,000

52000

52,000

60,000

29

Cast iron....................

18,000

81,000

25,000

45,000

12

Steel, castings..............

70,000

70,000

60,000

70,000

30

Brass, cast.....................

24,000

*30,000

36,000

20,000

9

Bronze, phosphor................

50,000

14

Bronze, aluminum.............

75,000

120,000

Aluminum, commercial

15,000

12,000

12,000

11

Table IX. Strength Of Timber In Pounds Per Square Inch

1

2

3

4

5

6

7

Material.

Ultimate Tensile with Grain.

Ultimate Compression Parallel to Grain.

Allowable Com. Perp. to Grain.

Ultimate Shearing.

Modulus of Rupture or Extreme Fiber Stress.

Modulus of Elasticity.

Parallel to Grain.

Perpendicular to Grain.

White oak........................................................

10,000

4,500

700

800

4,000

6,000

1,100,000

White pine ......................................................

7,000

3,500

250

400

2,000

4,000

1,000,000

Southern, Long-Leaf, or Georgia yellow pine

12,000

5,000

600

600

5,000

7,000

1,700,000

Douglass, Oregon, and yellow fir................

12,000

6,000

400

600

6,500

1,400,000

Washington fir orpine red fir.......................

10,000

5,000

Northern or Short-Leaf yellow pine.............

9,000

4,000

350

400

4,000

6,000

1,200,000

Red pine .........................................................

9,000

4,000

250

5,000

1,200,000

Norway pine...................................................

8,000

4,000

250

4,000

1,200,000

Canadian (Ottawa) white pine......................

10,000

5,000

350

Canadian (Ontario) red pine..........................

10,000

5,000

400

5,000

1,400,000

Spruce and Eastern fir...................................

8,000

4,000

300

400

3,000

4,000

1,200,000

Hemlock .........................................................

6,000

4,000

250

350

2,500

3,500

900,000

Cypress............................................................

6,000

4,000

250

5,000

900,000

Cedar.............................................

8,000

4,000

250

1,500

5,000

700,000

Chestnut..........................................................

9,000

5,000

350

600

1,500

5,000

1,000,000

California redwood........................................

7,000

4,000

300

400

4,500

700,000

California spruce............................................

4,000

5,000

1,200,000

The values for different woods in Table IX are average values for commercial timber. Column 3 in the table shows the ultimate compressive strength parallel to the grain, which values are used in figuring the ultimate strength of columns. Column 4 gives the allowable compressive strength perpendicular to the grain, the values given being the load per square inch of section required to produce an indenture of 1/100 of an inch. Reference to Fig. 1 will explain this more clearly. The left-hand portion of column 5 will be found of use in calculating the resistance of the timber at the heel of a roof truss. For instance, in Fig. 2, to calculate with what force the piece c of the tie member 6 opposes the thrust of the rafter member a. The sectional area of the surface d e f is 10 in. X 18 in. = 180 sq. in. The ultimate shearing strength of Georgia yellow pine, parallel with the grain, according to Table IX, is 600 lb.; then, 180 x 600 = 108,000 lb., the ultimate strength of the timber. If the safe strength is desired, divide by the required factor of safety; if 4 is used the safe strength will be 108,000 / 4 = 27,000 lb. Column 6, giving the modulus of rupture for different woods, is used in figuring the strength of beams (see page 106).

From recent tests to determine the physical properties of timber, made by the Forestry Division U. S. Dept. of Agriculture, the following conclusions are deduced: That the bleeding of long-leaf yellow pine, for sap products, is not detrimental to its durability and strength; that moisture reduces the strength of timber, whether that moisture be the sap or that absorbed after seasoning; also, that large timbers are equal in strength to small, provided they are sound and contain the same percentage of moisture.

Table IX Strength Of Timber In Pounds Per Square I 209

Fig. 1.

Table IX Strength Of Timber In Pounds Per Square I 210

Fig. 2.