Part 23

=51.= The building departments of several of the large cities stipulate that buildings of the second class, which includes factory construction, shall not have steel girders that are not fireproofed supporting brick walls or floors. When this construction is required, the secondaries must be supported as in Fig. 24 (_c_). In this view is two angle brackets riveted or bolted to the steel beam, and extending through the concrete for the support of the wooden beams. While there is some danger of heat being transmitted to the beams through the projecting ends of these brackets, nevertheless it is considered better construction than that shown in Fig. 24 (_d_), where stirrups are used over the concrete fireproofing. In this latter construction, there is a liability of the stirrup bending at _a_, _a_, and crushing the concrete beneath. Where the reaction from the end of the girder is great, this undoubtedly is likely to occur, and such stirrups should be provided with a bearing plate on top of the concrete, so that their bearing at the edge will be distributed over a considerable area.

TRAVELING-CRANE LOADS

=52. Planning for Traveling Cranes.=—In designing factories or mill buildings in which traveling cranes are to be installed, it is important to observe that the track of the crane can be properly supported, and also that there is sufficient headroom under the floor or roof construction to permit the trolley of the crane and the traveling mechanism of the crane girder to move underneath.

In Fig. 25, there is shown the upper portion of a steel-mill building. The columns _a_ support the girder carrying the runway of the crane. A convenient means of supporting the roof is to splice to this column a similar column _b_, which is incorporated in the design of the roof truss and rigidly braced with the truss by means of a knee brace at _c_. In the design of such a building, it is very important to determine the distances _x_ and _y_ required by the makers of the traveling crane. These distances _x, y_ depend on the size of the crane, that is, whether it is designed to carry 5, 10, 15, or more tons. Usually from 9 to 12 inches is sufficient for the measurement _x_, while the measurement _y_ varies from 5 to 8 feet.

=53. Cranes Supported on Reinforced-Concrete Walls.=—Frequently, in the latest types of construction, the runway for the crane is supported on reinforced-concrete walls, which construction is shown in Fig. 26 (_a_). It will be observed that the pilasters supporting the crane are strongly reinforced in all directions from which stresses are likely to be created from the eccentric load imposed by the crane track.

Where cranes are supported on reinforced-concrete columns, as in Fig. 26 (_b_), it would be good practice to put additional rods in the far side of the column as at _a_, in order to supply a greater resistance to bending, and thus counteract the effect of the eccentric load produced by the reaction from the crane track. Where cranes handle heavy rails or cumbersome material that might, by swinging, impose a blow on the reinforced-concrete columns, it is good construction to protect the edge of the columns with an angle iron as indicated at _b_. This angle iron may be fastened in the forms and anchored by means of pronged anchors back into the concrete when it is tamped.

=54. Detail of Track Construction.=—Many crane failures have been due to the spreading of the track between supports. It is better, therefore, to supply considerable lateral rigidity to the beam supporting the track or traveling crane. Where loads are heavy and plate girders are used for the runway tracks, the flanges of the girder are sufficient for this purpose. Where =I= beams are used, however, for the support of the crane track, it is good practice to place on the top of them and rivet with countersunk rivets, spaced about 18 inches apart on each flange, channel irons as indicated at _a_, Fig. 27. By means of these channel irons, which are drilled with open holes _b b_, the rail _c_ may be readily clamped in place by means of wrought-iron clips and bolts, and the rails nicely aligned and adjusted by wedging between these clips and the track.

=55. Maximum Stress on Track Girders.=—The principal calculation for the construction of the runway of cranes exists in determining the maximum bending moment. The maximum bending moment on a runway girder occurs when the wheels of the traveling crane are in the position indicated in Fig. 28. It will be noticed that the center of the girder is midway between the center of the near wheel and the center of the crane trolley, that is, the distance _a_ is one-half the distance _b_. The following formula will give the maximum bending moment on a crane girder when the load is in the position indicated in Fig. 28:

_w_(_l_ - _a_)² _M_ = --------------- 2_l_

in which _M_ = bending moment, in inch-pounds; _w_ = load on one wheel of crane, in pounds; _l_ = span of girder from center to center of support, in inches; _a_ = distance, in inches, marked in Fig. 28.

In order to illustrate the application of this formula, assume that the wheel load _w_ equals 10,000 pounds; that the distance from center to center of supports of the runway girder is 15 feet, or 180 inches; and that the distance _a_ is 12 inches. By substitution,

10,000 × (180-12)² _M_ = ------------------ = 784,000 inch-pounds 2 × 180

From this bending moment may be found, by the methods given in _Design of Beams_, the proper size girder to use.

THE POWER PLANT

BOILER ROOM

=56. Locating the Boiler Room.=—The ideal location for the boilers of a factory or an industrial plant is in a separate building, which may be denominated as the =power house=, and which may include as well, the installation of the engines, dynamos, and other machinery necessary for the generation of power and its transmission. More frequently, however, the ground is not available for the erection of a separate building for the power plant, and it becomes necessary to install the boilers and engines in the factory itself. The location usually selected for these vital features of the mill is the basement, and the arrangement of the boilers and engines must be carefully considered in the designing of this portion of the building.

=57.= In laying off the space to be occupied by the boilers, the probable growth of the manufactory must be provided for by arranging ample space for the installation of additional boilers.

It is best in arranging the boilers, to face them toward the available coal supply, which is usually a coal bunker, vault, or bin, but in no instance must the front of the boiler be nearer to a wall than the length of the boiler tubes, unless special arrangements are made, for this distance must be allowed in order to draw any defective or damaged tubes and replace them with new ones. Also, by arranging the boilers thus, the fireman has a minimum amount of carriage for the coal.

=58. Coal Storage.=—In designing the coal vaults, or coal storage, their contents should be figured to allow for 1 or 2 weeks’ coal supply, and as much more as is possible, to carry the plant over periods of existing coal shortage due to strikes or interrupted traffic from bad weather or other cause. In calculating the amount of space required for coal storage, it is sufficient to multiply the number of horsepower generated by the boilers by 4, which is the approximate number of pounds of coal per hour for the generation of 1 horsepower. This result, again multiplied by the number of hours for which the boilers are run at their capacity, will give the quantity of coal needed per day, in pounds. The weight per cubic foot of coal varies from 80 pounds for soft coal to 90 pounds for hard coal, so that by dividing the number of pounds by these quantities the cubic feet of coal required per day is obtained. The bins may then be proportioned for the number of days’ supply which the judgment of the designer may assume as being necessary.

=59. Ash Disposal.=—Besides the consideration of the coal supply, some disposition must be made of the ashes from the boilers. Frequently, a bin is constructed of masonry, alongside of the coal supply, into which the ashes are dumped by means of barrows. In large plants, this bin can be emptied by means of an ash conveyor, or elevator, which will carry the ashes to the level of the street or railroad track and thence into a cart or car.

=60. Planning the Boiler Room.=—In locating the boilers in the boiler room, which should be done in the plans of the building, for it is not customary to cement the floor space covered by the boilers, and the cost of the building is thus reduced, a passageway not under 3 feet, and better 4 feet, should be left back of the boilers. This passageway is required in order to have access to the clean-out doors and the blow-off cocks. The ordinary horizontal return-tubular boiler, and some water-tube boilers, can be constructed in a battery, with as many boilers as may be desired in a row, especially when the passageway is left back of the boilers. When setting other types of water-tube boilers, space should be left between each battery of two, for in these boilers, cast-iron doors are provided in the side walls for blowing the soot from the tubes, and access must be had through the side walls of the boiler for this purpose. It is therefore necessary in laying out the boiler space for boilers of this character to provide a passageway on one side of each boiler. In Fig. 29, a battery of return-tubular boilers is indicated, showing the clean-out doors for taking away the accumulation of soot and ashes that might be back of the bridge wall, through a passageway at the rear of the boilers. Some water-tube boilers are set in batteries of two, as the Babcock & Wilcox water-tube, land-type boiler, which is provided with the necessary clean-out doors, and doors for blowing the soot off the tubes in the side wall.

It is therefore necessary in laying out the boiler room of a manufacturing plant to consider carefully the character of the steam generator and study its requirements, so that it may be successfully operated and the proper spaces allotted.

=61. Doorway to Engine and Boiler Room.=—In the hasty design of buildings, it is frequently found that the size of the doorways is not sufficient to admit the boilers and machinery. This is a serious defect in the planning of a manufacturing plant, as it requires either the installation of the boilers and engines before the walls are entirely built, or else the tearing out of brickwork and jambs in order to accommodate them afterwards. An expedient for the enlargement of the headroom of doorways and openings into the boiler and engine rooms that are in the basement, is shown in Fig. 30. Here, if the lintel of the doorway _a_ is kept below the floor level, where it would ordinarily exist, the headroom of the doorway will be materially reduced, and considerable difficulty will be encountered in taking any large piece of machinery, or a boiler or steam drum, down the steps _b_. The doorway is consequently increased in height by the introduction of the bulkhead at _c_; while by this means the floor space above is slightly reduced, yet use can frequently be found for the ledge or platform frame at the top of the bulkhead, as at _d_.

=62. Floors Above Boilers.=—It is important in designing boiler rooms in factories to have the floor construction over the top of the boiler of incombustible material, and it is customary in the better class of buildings to provide a section of fireproof floor over the top of the boiler room. This floor construction may either be a brick arch supported on steel beams, or hollow-tile construction, though reinforced concrete is now finding favor in this purpose.

=63.= It is not altogether necessary that the boilers in a building shall be placed in the basement, though as this is usually the least valuable of the floor space it is the practice to so locate them. In some electric-light stations, and in large factories, boilers have been located on the first floor, and even in several instances on the fifth and sixth floors. The exigencies that demand the latter installation, however, must be great, for it can be readily seen that much power must be expended in lifting the coal, etc. to the boiler room.

CHIMNEYS

=64. Dimensions and Capacity of Chimneys.= Nearly all the factory buildings combine in their structure a power plant, not the least important feature of which is the =chimney=. There are two things to consider in the design of a power chimney—first, its capacity for providing the necessary draft and the conduction of the requisite volume of gases from the furnace or boiler, and second, its stability. The first requirement regulates its diameter and height, and these dimensions, together with its construction, determine also its stability.

TABLE I

=====+===========================================================+====+======+====== | | |Effec-| | Height of Chimneys and Commercial Horsepower Capacity |Side| tive |Actual Diam-+---+---+---+-----+-----+-----+-----+-----+-----+-----+-----+ of | Area | Area eter |50 |60 |70 | 80 | 90 | 100 | 110 | 125 | 150 | 175 | 200 | Sq.|Square|Square In. |Ft.|Ft.|Ft.| Ft. | Ft. | Ft. | Ft. | Ft. | Ft. | Ft. | Ft. | In.| Ft. | Ft. -----+---+---+---+-----+-----+-----+-----+-----+-----+-----+-----+----+------+------ 18 | 23| 25| 27| | | | | | | | | 16| .97| 1.77 21 | 35| 38| 41| | | | | | | | | 19| 1.47| 2.41 24 | 49| 54| 58| 62| | | | | | | | 22| 2.08| 3.14 27 | 65| 72| 78| 83| 87| | | | | | | 24| 2.78| 3.98 30 | 84| 92|100| 107| 113| 119| | | | | | 27| 3.58| 4.91 33 |105|115|125| 133| 141| 149| | | | | | 30| 4.48| 5.94 36 |128|141|152| 163| 173| 182| 191| | | | | 32| 5.47| 7.07 39 |154|168|183| 196| 208| 219| 229| | | | | 35| 6.57| 8.30 42 |182|200|216| 231| 245| 258| 271| 288| | | | 38| 7.76| 9.62 48 | |269|290| 311| 330| 348| 365| 389| | | | 43| 10.44| 12.57 54 | |348|376| 402| 427| 449| 472| 503| 551| | | 48| 13.51| 15.90 60 | |436|471| 503| 536| 565| 593| 632| 692| 748| | 54| 16.98| 19.64 66 | | |579| 620| 658| 694| 728| 776| 849| 918| 981| 59| 20.83| 23.76 72 | | |698| 746| 792| 835| 876| 934|1,023|1,105|1,181| 64| 25.08| 28.27 78 | | | | 885| 949| 990|1,038|1,107|1,212|1,310|1,400| 70| 29.73| 33.18 84 | | | |1,035|1,098|1,157|1,214|1,294|1,418|1,531|1,637| 75| 34.76| 38.48 90 | | | | |1,269|1,338|1,403|1,496|1,639|1,770|1,893| 80| 40.19| 44.18 96 | | | | | |1,532|1,606|1,712|1,876|2,027|2,167| 86| 46.01| 50.27 100 | | | | | | |1,760|1,865|2,043|2,197|2,359| 89| 50.11| 54.54 104 | | | | | | |1,899|2,024|2,218|2,395|2,560| 93| 54.39| 59.00 108 | | | | | | |2,051|2,190|2,399|2,591|2,770| 96| 58.83| 63.62 112 | | | | | | | |2,323|2,588|2,795|2,983| 100| 63.46| 68.42 118 | | | | | | | |2,632|2,883|3,114|3,339| 105| 70.71| 75.94 120 | | | | | | | |2,725|2,986|3,225|3,447| 107| 73.22| 78.54 124 | | | | | | | |2,915|3,193|3,449|3,687| 110| 78.31| 83.86 130 | | | | | | | |3,165|3,467|3,745|4,004| 116| 85.04| 90.76 136 | | | | | | | | |3,868|4,178|4,466| 121| 94.85|100.88 142 | | | | | | | | |4,305|4,567|4,886| 126|103.69|109.98 150 | | | | | | | | |4,719|5,097|5,448| 133|115.72|122.72 =====+===+===+===+=====+=====+=====+=====+=====+=====+=====+=====+====+======+======

Considering the first requirement, a circular flue is considered more efficient than a square one, because its inside surface offers less resistance to the passage of the gases, and there is not the likelihood of eddies being formed. There is much difference of opinion among engineers as to whether a stack should be narrower toward the top or increased in size. The practice is to taper a stack toward the top, this being done more on account of the necessity for increasing its stability than because of the draft. Some stacks have been built, however, with a larger inside diameter at the top than at the bottom, with the idea of providing a greater sectional area for the passage of the gases as their velocity is decreased. The capacity of the stack for carrying off the products of combustion depends on the temperature of the inside gases as compared with the temperature of the outside air. The average temperature in stacks for power purposes ranges from 450° to 600° F., and, therefore, as there is little difference in the travel of gases in flues between these temperatures, Table I can safely be used in determining the diameter and height of stack for a given capacity of power plant.

In Table I, it will be observed that the capacity of the stack is given in horsepower, and in calculating this table it was considered that 5 pounds of coal were burned to develop 1 horsepower, this being a high figure with the present economical systems of power generation. Allowance has also been made, in this table, for the friction of the gases against the side walls of the stack, it being considered that a 2-inch layer of dead air exists between the stack lining and the gases.

=65. Stability of Brick Chimneys.=—In considering the stability of brick stacks, the overturning moment due to the wind must not exceed the resisting moment of the stack to overturning about the base. For instance, referring to Fig. 31, the pressure _p_ due to the wind acts with the lever arm _x_ about the base of the stack, tending to overturn it. The stack, or chimney, resists this overturning moment with its weight _w_, acting through a lever arm _y_; if these two moments are equal, the stack can be considered safe under the conditions considered, though it is better to have some factor of safety, 2 usually being sufficient. An easy formula by which to determine whether a stack is stable or not, is as follows:

_h_² × _dc_ _w_ = ------------ b

in which _w_ = weight of stack, in pounds; _h_ = height of stack, in feet; _d_ = mean diameter of stack, in feet; _c_ = constant; _b_ = width of base.

The constant _c_ varies with the shape of the stack. For a square stack, when the wind is blowing at hurricane violence, 56 is used; for an octagonal stack, 35; and for a round stack, 28.

To demonstrate this formula, consider a square chimney having an average breadth of 8 feet and a width at base of 10 feet, the stack being 100 feet high. The problem is, therefore, to find what the weight of the stack must be in order to resist the greatest wind pressure likely to occur. By substitution, in the formula,

100 × 100 × 8 × 56 _w_ = ------------------ = 448,000 pounds 10

With brickwork weighing about 120 pounds per cubic foot, the chimney in question must therefore have an average thickness of somewhat more than 13 inches.

=66.= A good rule to follow in designing brick stacks is to make the base at least one-tenth of the height. For stacks under 5 feet in diameter, the walls for the first 25 feet from the top may be 8 inches, increased 4½ inches for each additional 25 feet from the top. If the stack is more than 5 feet in diameter, the thickness at the top should be 1½ bricks, or 12 inches, with a 4½-inch increase for each 25 feet. If the stack is less than 3 feet in diameter, the brickwork for the first 10 feet from the top may be as little as 4½ inches; this thickness, however, is not recommended, as the weather is likely to penetrate such a thin wall, and sooner or later, together with the exposure to the gases, destroy the brickwork.

=67. Construction of Brick Chimneys.=—All brick stacks must be provided with a cast-iron or stone coping at the top, and it is usually well to tie them in toward the base with good heavy stone band courses. In constructing brick stacks, the brickwork should be laid up in lime-and-cement mortar, and the bricks well covered and slid in place, not just tapped or hit with the handle of a trowel.

All chimneys should also be provided, for a distance of at least one-third of their height from the base, with a fire-brick lining, laid up in fireclay, and at the bottom of this lining, where the flues from the boiler enter the stack, cast-iron cleaning doors and frame should be provided for removing soot that will accumulate and drop down. A good example of a brick stack is given in Fig. 32; this stack has a capacity of 500 horsepower, and is sufficiently stable to resist any wind pressure.

FIRE-PROTECTION OF MILL BUILDINGS

SPRINKLER SYSTEM

=68. Sprinkler Tanks.=—In the large cities, where fire risks are great, and where nearly all the buildings and their contents are protected by insurance, the owners of the buildings are subjected to the rules and regulations of the Underwriters, or Associations of Insurance Companies. These Underwriters from time to time pass regulations insisting on certain further precautions and protection against fire, such as the installation of sprinkler systems, stand pipes for hose attachment for each floor, etc.

As the available city pressure or water supply of the municipality may be limited, or uncertain, or the pressure too low for a high building, it is sometimes necessary to place water tanks of from 10,000 to 30,000 gallons capacity in towers on the roofs of factories, and in the design of new factories provision is usually made for three tanks.

In designing a building, these tanks are located at such a point that their support is insured by the walls beneath, and the most convenient place is found to be over the stair tower or adjacent to it. As 1 gallon of water, together with the tank containing it, has a unit weight of 8 pounds, a 30,000-gallon tank complete will weigh in the neighborhood of 240,000 pounds, which must be supported on the walls and by means of iron beams.

The architect, besides providing adequate support for these tanks, must so design the tanks as to secure them against bursting, which would lead to serious consequences. For durability, sprinkler or fire-protection tanks are made of either cypress or cedar from 2 to 3 inches in thickness. They are usually in the shape of a truncated cone, and the bottom of the tank is required to be at least 20 feet above the highest point of the top story.