Miscellaneous Loads

In special cases there will be other loads to provide for besides the more common roof, floor, crane, snow and wind loads just considered. The bottom chords of roof trusses are frequently employed to carry shafting, steam pipes, trolleys, etc. It is sometimes convenient also to have the roof trusses sufficiently strong to permit of a block and tackle being attached at any point to handle goods. The roof may require a ventilator and when it does this extra weight must be added to the roof loads. Columns in exposed places where they are liable to shocks from vehicles or merchandise should be made stronger than those built into brick walls.

Summary Of Loads

The total roof loads per square foot of roof, including weights of trusses for spans under 75 ft., is about as follows for different constructions of roofing:

Style of Construction.

Lbs. per sq. ft.

Corrugated iron, unboarded.....

8

" " on boards...........

11

Slate on laths..........

13

" " 1 1/4-in. boards............

16

Tar and gravel..............

12

Shingles on laths.............

10

Tile.....................

20 - 30

When any of these roofs are plastered below the rafters 10 lbs. per square foot should be added to the loads given. For spans greater than 75 ft. a weight of 4 lbs. per square foot should be added to the weights given. For snow and wind loads combined add for northern latitudes 30 lbs. per square foot to the loads given.

The weight of steel in the sides and roofs of mill buildings, without cranes, is from 4 lbs. to 6 lbs. per square foot of exposed surface for the frame only. Corrugated iron sheathing weighs from 1 lb to 2 lbs. per square foot. These weights, with steel at 5 cts. per lb., make the cost of steel buildings from 25 cts. to 40 cts. per square foot of exposed surface. A rough approximate rule for calculating the extra weight of steel required in columns and girders when traveling cranes are used is as follows: Add 100 lbs. of steel per lineal foot of building for every five tons of crane capacity. This would give for a 5-ton crane an addition of 100 lbs. per lineal foot and for a 20-ton crane an addition of 400 lbs. per lineal foot.

Methods Of Calculation

Methods of calculation will not be touched upon in this book, since they may be found in any text-book upon the subject. Briefly enumerated, the cases to be considered in determining strains are the following:

(1) Strains in roof trusses and columns from permanent dead loads.

(2) Roof trusses on walls, strains from wind normal to the surface.

(3) Wind on side of building and roof, strains in trusses, columns and knee braces; (a) columns hinged at the base; (b) columns fixed at the base.

Partial loading can never cause maximum srains in the parts of a Fink truss as they may in other forms of roof trusses.

Table I. Showing Weights of Merchandise as Given by C. J. H. Woodbury in his Book on "Fire Protection of Mills."

Wool in bales..............

17 to 29 lbs. per cu. ft

Woolen goods.................

16 to 22 " "

Baled cotton..........

20 to 40 " "

Cotton goods............

16to40 " "

Rags in bales...............

15to36 " "

Strawboard, newspaper and manilla.........

33to 44 " " "

Calendered and super-calendered book......

50 to 70 " " "

Writing and wrapping paper..................

70to90 " " "

Wheat...............

39to44 " " "

Flour......

40 " " "

Corn......

31 " " "

Corn meal............

37 " " "

Oats.............

27 " " "

Baled hay............

57 " " "

Compressed hay and straw............

19 to 30.......... " " "

Bleaching powder............

31

Soda ash.............

62 " " "

Indigo...........

43 " " "

Cutch...........

45 " " "

Sumac............

39 " " "

Caustic soda............

88 " " "

Starch

23 " " "

Alum........

33 " " "

Extract logwood.....

70 " " "

Lime....

50 " " "

Cement, American............

59 " " "

Cement, English..............

73 " " "

Plaster.............

53 " " "

Rosin.............

48 " " "

Lard oil..........

34 " " "

Rope.....

42 " " "

Tin.....

278 " " "

Glass

60 " " "

Crockery..............

40 " " "

Leather in bales........

16 to 23 " " "

Sugar...........

42 " " "

Cheese............

30 " " "

Table II. Showing Maximum Weight in Pounds Which Will Come on End Wheels of Traveling Crane When the Fully-Loaded Trolley is at the Same End.

Capacity, in tons.

Span of crane In feet.

25

30

35

40

45

50

55

60

5......

31,700

32,870

33,800

34,900

35,900

37,200

38,600

40,300

10......

45,100

46,000

47,400

48,900

50,200

51,600

53,200

55,700

20......

. 72,100

74,100

75,800

77,600

79,400

82,000

83,900

86,100

30......

.103,800

108,200

110,000

112,600

115,200

117,700

120,400

122,800

50.....

.152,300

158,100

162,200

167,500

171,600

175,600

178,600

182,400

Table III. Giving the Normal Pressures from Wind on Roofs of Different Slopes for a Wind Pressure of 30 lbs. per Square Foot Against a Vertical Plane.

Angle.

Pressure.

5

3.9

10

7.2

15

10.5

20

13.7

Angle.

Pressure.

25

16.9

30

19.9

35

22.6

40

25.1

Angle.

Pressure.

45

27.1

50

28.6

55

29.7

60

30.0