Designing Iron Roofs Continued 100337Designing Iron Roofs Continued 100338Designing Iron Roofs Continued 100339Designing Iron Roofs Continued 100340Designing Iron Roofs Continued 100341Designing Iron Roofs Continued 100342

Shoe of cast iron; Tension Rods, flat bars; and Tie Rod, double flat bars. A Ventilator extends along part of the roof, details of which are given in Figs. 429 and 434 to 436.

Plate X. is a section of a workshop roof, so arranged as to admit light from one side only, which should be the north, and called from its shape, a Saw-tooth roof. The Truss is of the queen-rod type; Rafters and Struts, T iron; Tie and Tension Rods, round iron; Head, joint with plates; Shoe, lug cast on top of column; Covering, zinc, on boarding, except on north side when one of the many systems of glazing without putty (Rendles, see Part II.) is used.

Cost

This subject is outside the scope of these Notes, but will be found well treated in Adam's Designing Wrought-and Cast-iron Structures. Part V.

Cost 100343

Fig. 390.

Proportions of Trussed - rafter Roofs (see Fig. 390) from 20 to 45 feet span.1 Rise = 1/5 span. Camber of tie rod = 1/30 span. Principals 6' 8" apart.

Span in feet.

Rafter T iron. Dimensions in inches.

Diameter of Tension Rods in Inches.

Between heads of Struts.

Between head of

Strut and foot of Rafter.

Between head of

Strut and apex of Roof.

R

X

Z

Y

20

2 1/2

by

2

by

3/8

5/8

7/8

5/8

25

2 3/4

,,

2

,,

3/8

3/4

1

3/4

30

2 3/4

,,

2 1/2

,,

1/2

2 1/4

by

1/4

2 1/4

by

3/8

2 1/4

by

1/4

35

3

,,

2 3/4

,,

1/2

2 1/2

,,

5/16

2 1/2

,,

1/2

2 1/2

,,

5/16

40

3 1/4

,,

3

,,

1/2

2 1/2

,,

3/8

2 1/2

,,

5/8

2 1/2

,,

3/8

45

4

,,

3 1/2

,,

1/2

3

,,

3/8

3

,,

1/2

3

,,

3/8

1 From Molesworth's Pocketbook of Engineering Formula:.

Cost 100344

Fig. 391.

Proportions of Wrought-iron Queen-bolt Roofs (see Fig. 391) from 20 to 40 feet span usually adopted in practice.1 Rise = 1/4 span. Camber of tie rod = 1/30 span. Distance apart of trusses 8 feet.

Span.

Tie Rod, Diameter.

Bolts, Diameter.

Struts, Sectional Area.

T Rafters.

f

g

i

k

l

m

R

Feet.

"

"

"

"

"

"

Inches.

20

15/16

13/16

1/2

5/8

0.8

0.9

3 1/4

X

2 1/2

X

7/16

22

15/16

7/8

1/2

5/8

0.9

1.0

3 1/2

X

2 1/2

X

7/16

24

1

7/8

1/2

11/16

1.0

1.1

3 1/2

X

2 3/4

X

7/16

26

1 1/16

15/16

1/2

11/16

1.1

1.2

3 3/4

X

2 3/4

X

7/16

28

1 1/16

1

1/2

11/16

1.2

1.3

4

X

2 3/4

X

7/16

30

1 1/8

1

1/2

3/4

1.2

1.4

4

X

3

X

1/2

32

1 3/16

1 1/16

1/2

3/4

1.3

1.5

4 1/4

X

3

X

1/2

34

1 3/16

1 1/16

1/2

13/16

1.3

1.5

4 1/2

X

3

X

1/2

36

1 1/4

1 1/8

1/2

13/16

1.4

1.6

4 1/2

X

3 1/2

X

1/2

38

1 1/4

1 1/8

1/2

13/16

1.5

1.7

4 3/4

X

3 1/2

X

1/2

40

1 5/16

1 3/16

1/2

13/16

1.5

1.7

4 3/4

X

3 1/2

X

5/8

1 From Hurst's Architectural Surveyor's Handbook.