In practice bricks are subjected to compression, and sometimes to transverse stress, but not to tension.

The compressive stress brought upon evenly-bedded bricks is generally far less than they are able to bear.

In some cases, however, as in arches and retaining walls, the stress may be concentrated upon a small portion of the brick, or the same effect may be produced by the bed of the brick being uneven.

Such concentrated stresses are apt to crack the portion of the brick upon which they act.

Resistance Of Bricks To Compression

Description of Brick.

Dimensions of Specimen.

Area exposed to Crushing.

Average

Weight under which

Brick

Cracked.

Average Weight required to crush Brick.

Weight required per Square

Inch to crush

Brick.

Authority.

Length.

Breadth.

Thickness.

Unburnt Brick

8.875

4.375

2.875

Sq. Inches.

Tons.

Tons.

Tons.

G

38.83

1.0

9.0

.23

Common Red .

9.07

4.27

3.0

387

9.5

57.0

0.96

L

Machine-made form ed Red

9.3

4.4

3.3

40.9

23

33

.791

L

Common Stock

8.9

4.07

2.55

36.2

10

128

3558

L

Sittingbourne Stocks

8.81

4.13

2.50

36.35

5.7

33.9

.93

G

Farebam Reds .

8.50

4.25

2.62

36.13

8.42

26.1

•72

G

Do. Rubbers

10.19

4.88

2.94

49.64

1.40

15.7

•32

G

Tipton Blue .

875

4.31

2.50

37.73

21.26

95.20

•39

G

Exbury Best .

8.875

4.25

2.75

37.73

21.0

28..5

•76

G

Do. Second .

.8.875

4.25

2.75

37.73

21.0

39.0

•77

G

Do. Third .

8.50

41

2.6

35.06

11.3

29.0

•83

G

Suffolk Brimstone .

9.06

4.56

2..69

41.34

51

31.0

•77

G

Do. Best Whites .

9.19

4.56

2.62

41.9

5.1

19.6

•47

G

Gault

8.75

4.25

2.75

37.18

12.7

351

•94

G

Wire-cut White Gault

9.04

4.33

2.72

39.1

11.0

53

1.35

L

Pressed Gault .

8.9

4.33

2.68

38.2

8.0

46.5

1.23

L

Gault Wire-cut, No. 2

8.63

4.0

2.63

34.50

6.4

32.90

•95

G

Do. Pressed, No. 1

875

4.19

2.69

36.64

7.4

36.80

1.0

G

Staffordshire Dressed Blue

9.07

4.47

2.97

40 3

15.5

114.

2.803

L

Staffordshire Pressed Blue

8.93

4.46

2.88

39.8

21.5

73

1.861

L

Staffordshire Common Blue

9.39

4.38

3.01

41.1

13.0

39

.954

L

Staffordshire Bastard

9.23

4.58

3.21

41.2

27.0

41.5

1.006

L

Brown Glazed Brick

9.0

4.39

3 39

39.5

16

23

.579

L

G, Grant's Experiments, Proceedings Inst. Civ. Engineers, vol. xxv. pp. 35-38. L, Baldwin Latham's Sanitary Engineering, p. 122.

The resistance of bricks to crushing is much reduced when they are built into work, being greatly influenced by the nature of the mortar used.

The following are the results of experiments made by Mr. Kirkaldy for the new Blackfriars Bridge : -

Bricks used in Piers.

Size of Piers.

Cementing Material.

Tons per Foot sup.

At which failure began.

At which crushing took place.

Common Stocks, recessed one side

Inches 14x14

Lime Mortar

17

27

Do, do.

Do.

Do.

21

30

Red Bricks (machine made)

Do.

Do.

20

40

Do. (hand made) .

Do.

Do.

20

36

Gault Bricks ....

Do.

Roman Cemeut

24

59

Do......

9x9

Do.

54

72

Clark's Sudbury (machine made)

Do.

Portland Cement

49

76

Uxbridge Red (hand made)

Do.

Do.

44

53

Transverse Strength Of Bricks

The only records, known to the writer, of experiments on the transverse strength of bricks do not state how the weight was applied, so that they are valueless.

Tensile Strength Of Brick

The tenacity of brick is given by the late Professor Eankine as varying from 280 to 300 lbs. per square inch.

The writer is not aware of any reliable record of experiments on this point.