This section is represented in Fig. 14. The web is rolled with parallel sides, the flanges are tapered and connected to the web with rounded internal angles, and this is the type of the British standard section. Increase of weight beyond the minimum section is obtained mainly by an increase in web thickness.

This section is frequently used as a beam in small bearers, as a strut in the compression members of lattice girders and roof trusses, and in riveted columns, while it is occasionally useful in certain connections as taking the place of two angles.

If a small section of channel is required having a rivet through the web, as, for example, in the case of two channels crossing one another, back to back, and riveted together, care must be taken in the selection to secure one wide enough to permit of the formation of the point of the rivet. For this reason in such cases a small angle will frequently be found preferable to a small channel.

Channels 15

Fig. 14.

As in rolled joist sections so in channels, no generally recognized standard of proportionate thickness in web or flanges appears to have been attained prior to the establishment of the British standard section. In the majority of cases the thickness of web and flanges is similar or nearly so, but occasional sections are found where the thickness of flange is greater than that of the web. Any increase in weight over the normal or minimum section is obtained by thickening the web, the flange thickness remaining practically constant.

In the following table the thickness of web and flanges is assumed as uniform all over. The standard thickness of the British standard channel shows a flange thickness greater than that of the web, and the student is referred to the "Properties of British Standard Sections" for the corresponding mechanical values.

Table No. 28. The Principal Mechanical Elements Of Channels

(See Fig. 14)

Section of channel.

Area in square inches.

Weight in lbs. per foot run.

Moment of inertia about the axis a - b.

Fig. 14.

Radii of gyration.

Distance of axis a - b from farthest edge of section.

Axis a - b.

Axis c - d.

15¾"

X

3"

X

½"

10.37

35¼

308.2

5.45

0.74

7.87

15"

X

4"

X

⅝"

13.59

46¼

393.8

5.38

1.01

7.50

12"

X

4"

X

½"

9.50

32¼

187.8

4.45

1*14

6.00

12"

X

3½"

X

½"

9.00

30½

171.2

4.36

0.97

6.00

12"

X

3"

X

7/16"

7.48

25½

138.5

4.30

0.81

6.00

12"

X

2½"

X

½"

8.00

27§

138.1

415

0.62

6.00

11⅞"

X

3'

'X

½"

8.43

28¾

150.5

4.22

0.81

5.93

10"

X

4"

X

7/16"

7.50

25|

107.8

3.79

1.17

5.00

10"

X

3"

x

7/16"

6.62

22½|

87.8

3.64

0.83

5.00

10"

X

2½"

'X

7/16"

6.18

21

77.8

3.55

0.66

5.00

9⅞"

X

3⅛"

X

7/16"

6.66

22|

87.5

3.62

0.88

4.94

9¼"

X

3½"

X

7/16"

6.72

22¾

81.0

3.47

1.00

4.62

9"

X

3

X

7/16"

6.62

22½

75.7

3.38

1.00.

4.50

9"

X

3"

X

⅜"

5.34

18¼

59.4

3.33

0.86

4.50

9"

X

3⅛"

X

⅜"

4.96

17

52.4

3.25

0.68

4.50

8¼"

X

2½'

X

7/16"

5.41

18½

48.0

2.98

0.68

4.12

8"

X

3½"

X

½"

7.00

23§

63.58

3.10

1..00

4.00

8"

X

2½"

X

½"

6.00

20½

49.50

2.87

0.68

4.00

8"

X

2¼"

X

⅜"

4.40

15

36.45

2.88

0.61

4.00

Section of channel.

Area in square inches.

Weight in lbs. per foot run.

Moment of inertia about the axis a - b.

Fig. 14.

Radii of gyration.

Distance of axis a - b from farthest edge of section.

Axis a - b.

Axis c - d.

8"

X

2"

X

⅜"

4.22

14½

33.73

2.83

0.51

4.00

7⅞"

X

3¾"

X

½"

7.18

24½

64.60

3.00

1.13

3.94

7⅞"

X

3⅛"

X

½"

6.56

22¼

56.10

2.92

0.91

3.94

7⅞"

X

"2

X

⅜"

4.55

15½

37.69

2.88

0.68

3.94

7"

X

3½"

X

½"

6.50

22¼

46.04

2.66

1.10

3.50

7"

X

3"

X

½"

6.00

20½

40.75

2.61

0.88

3.50

7"

X

2"

X

⅜"

3.84

13

24.10

2.51

0.53

3.50

6"

X

4"

X

½"

6.50

22¼

35.54

2.34

1.24

3.00

6"

X

3½"

X

⅜"

4.59

15¾

25.31

2.34

1.01

3.00

6"

X

3"

X

⅜"

4.22

14½

22.34

2.30

0.91

3.00

6"

X

2½"

X

⅜"

3.84

13¼

19.37

2.24

0.73

3.00

6"

X

2"

X

⅜"

3.47

12

16.40

2.17

0.55

3.00

6"

X

1¾"

X

5/16"

2.78

9½

12.89

2.15

0.42

3.00

5¾"

X

2⅜"

X

½"

4.75

16¼

20.87

2.10

0.71

2.87

5½"

X

2½"

X

⅜"

3.65

12!

15.68

2.07

0.74

2.75

5⅛"

X

2⅞"

X

½"

4.94

17

18.32

1.92

0.86

2.56

5"

X

2"

X

⅜"

3.09

10½|

10.43

1.84

0.58

2.50

5"

X

1½"

X

⅜"

2.72

9¼

8.42

1.76

0.40

2.50

4½"

X

2"

X

⅜"

2.90

10

8.05

1.66

0.58

2.25

4½"

X

1½"

X

⅜"

2.53

8½

6.45

1.60

0.41

2.25

4⅛"

X

2½

X

⅜"

3.14

10¾

7.81

1.57

0.75

2.06

4"

X

1¾"

X

5/16"

2.14

7¼

4.73

1.49

0.42

2.00

4"

X

1½"

X

.-» II 16

2.00

7

4.19

1.45

0.41

2.00

3½"

X

1½"

X

⅜"

2.15

7¼

3.42

1.26

0.43

175

3"

X

l½"

X

¼"-

1.37

4¾

1.75

1.13

0.45

1.50

2⅜"

X

1 3/16"

X

¼"

1.06

3¾

0.81

0.87

0.35

1.18

2¼"

X

1¼"

X

¼"

1.06

3¾

0.74

0.83

0.38

1.12

2"

X

1⅛"

X

¼"

0.94

3¼

0.50

0.73

0.33

1.00

1¾"

X

5"

8

X

3/16"

0.49

1¾

0.18

0.61

0.18

0.87

1½"

X

1¼"

X

3/16"

0.68

2½

0.23

0.58

0.38

0.75

1½"

X

¾"

X

3/16"

0.49

l¾

0.14

0.53

0.22

0.75

Further reference will be made to the use of channels in the practical design of columns or struts.