SAFE STRENGTH OF ROUND TANK HOOPS
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Diameter | Steel | Wrought Iron
Inch | Pounds | Pounds
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⅝ | 3,232 | 2,424
¾ | 4,832 | 3,624
⅞ | 6,720 | 5,040
1 | 8,800 | 6,600
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=71.= To illustrate the foregoing, assume that it is desired to find
what will be the spacing of ⅞-inch steel hoops at the bottom of a tank
12 feet in diameter, in which the water-line is 16 feet from the middle
of the section under consideration. Applying the formula in Art. =70=,
using in conjunction therewith Table II, it is found that
5.16 × 144 × 16
_N_ = --------------- = 1.77.
6,720
This result, 1.77, is the number of hoops required in 12 inches of
height from the bottom of the tank, and would indicate that the hoops
should be spaced about 7 inches from center to center, for 12 inches
divided by 1.77 gives approximately 7 inches, the pitch of the hoops.
This process should be repeated for different points throughout the
height of the tank, and from the results the tank may be designed.
=72.= In the installation of sprinkler tanks, it must be observed
that they are placed some distance above the highest point of the top
floor, the distance usually required by the Underwriters being 20 feet,
if it is possible of attainment. The tank should always be roofed,
have a ladder from the roof of the building to its top, and a steam
pipe inside to prevent the water from freezing in winter. This pipe
is furnished with a check-valve to prevent the water in the tank from
siphoning.
EXAMPLE FOR PRACTICE
What should be the spacing of the ¾-inch round wrought-iron
hoops on a tank 10 feet in diameter and 12 feet high at a
distance of 6 feet from the water-line?
Ans. 12 in.
=73. Automatic Sprinkler System.=—The sprinkler system as now installed
for protection against fire in the interior of a building consists
essentially of piping connected to a gravity tank and extending over
the entire ceiling by means of mains and branches. There is located on
the ends of the branches automatic valves or stops, which are collapsed
or opened by the melting of a fuse or solder at a temperature more than
is likely to exist in the room at any time and still below that which
would be created by an incipient fire.
=74.= The underlying principles of automatic sprinkler systems as
stated by the Underwriters are as follows:
1. Buildings must be open in construction, free from concealed spaces,
or places where water thrown from sprinklers cannot penetrate.
2. Sprinklers to be so located that their distribution will cover all
parts of the premises.
3. Sprinkler piping to be of sufficient capacity and to have water
under pressure in same at all times, except in case of a system where
freezing is likely to occur, where an air lock is used.
4. An automatic supply of water of sufficient quantity and pressure
available at all times.
5. Systematic, thorough, and intelligent care and inspection of the
system.
=75. Fireproof Windows.=—It is frequently necessary, and in many cases
required by law, and especially recommended by the Underwriters, to
provide fireproof window frames and sash in walls exposed to great fire
risk, or where it is necessary to admit light into elevator shafts or
fire-towers. To meet this demand, several forms of metallic window
frames and sashes have been evolved, and these sashes when intended as
a fire-retarder are always glazed with wired glass.
=76. Wired Glass.=—The wire glass now in common use consists of heavy
glass plate with wire mesh embedded in it. This glass is obtainable
in polished, ribbed, prism, or mazed form, as shown in Fig. 35 (_a_),
(_b_), (_c_), and (_d_), respectively. The plain glass, Fig. 35 (_a_),
is used where the light is ample, and where it is desired for the
occupants to see through the windows. The ribbed is employed usually in
factories, and the ribs are generally run in a horizontal direction, so
as to throw the light toward the ceiling and floor, thus diffusing it
throughout the building. The prism glass is also employed in order to
secure a greater diffusion of the light than is possible with the plain
or factory ribbed glass, while the mazed glass finds favor where it is
necessary to employ an obscured sash, which will still admit plenty of
light and present a good appearance but yet cannot be seen through.
The glass used in metallic frames should not be less than ½ inch, or,
if polished, ⁵/₁₆-inch, and the embedded wire should not have a mesh
larger than 1 inch and should not be less in size than No. 22 Brown &
Sharpe wire gauge, which is the standard used in America.
[Illustration: FIG. 35]
[Illustration: FIG. 36]
=77. Design of Sash.=—In designing a sash for fire-retarder frames,
it is necessary, in order to comply with the Underwriters rules and
regulations, to observe that no single light exceeds 24 in. × 30 in.
The metallic frames are generally constructed of No. 22 galvanized
steel, while the sash are made of a lighter weight, generally No. 24.
In unusual localities, where the frames are likely to be subjected to
the influence of gases, with known affinity for iron or galvanizing, it
is permissible to make the metallic frames of 18-ounce copper, though
such frames are not considered the equivalent of an iron frame as a
fire-retarder, and such frames should never be used in elevator, vent
shafts, or fire-retarder partitions that are liable to intense internal
fires.
In order to better explain the construction of the commercial frames,
Fig. 36 is given, which illustrates one of the best frames in the
market. In the figure, a vertical cross-section through the window-head
sill and parting rail is illustrated. It will be observed that
these frames can be neatly framed with architrave mold and stop, as
designated at _a_ and _b_. It will also be observed that the head for
the top sash is beveled, as indicated at _c_, so that a tight joint
is insured by the edge of the sash coming in contact with the bevel,
and thus compelling a close connection. The parting rails are also
constructed with a straight piece entering on a bevel _d_, so that at
this point a tight joint is also secured. By the several offsets in the
sill, wind and rain stops are provided, as indicated at _e_. Sashes
constructed in this manner can be made to slide freely, noiselessly,
and be made tight against weather and wind, as well as being secured
against annoying clattering, or rattling. The sills of metallic frames
are generally filled with cement, and sometimes the heads are similarly
made solid. Any unusually large surfaces, like that which would occur
between twin or triple windows, in the mullion, are securely braced
inside with galvanized sheet iron or bar iron.
=78.= In the construction of metallic sash, solder is never used for
holding the parts together, for all parts must be either lock-seamed or
riveted, the lock seams being illustrated at _g_, Fig. 36. Soldering
may be used only to fill up the joints. The objection to a joint that
is only soldered and not lock-seamed is that in a severe fire when the
window is subjected to an intense heat, the joint is apt to open by the
solder melting out. When the joint opens, flames may go through and the
fire-stop will thus be soon destroyed.
In designing the frames, they should have at least a 4-inch lap on
the brick reveal on the sides and head, and it is not uncommon to
wind-stop the sill by extending upwards a piece of galvanized sheet
iron. While such windows as those described will act as a fire-retarder
and prevent flames from reaching apartments that they protect, even
in cases of severe conflagrations, nevertheless the glass radiates
considerable heat, and inflammable goods should not be stored too close
to such windows. Neither is it particularly desirable to have window
shades secured to the frames of metallic windows. Where the goods in a
building are particularly inflammable, the liability to pile them too
close to the sash should be entirely eliminated by using window guards,
which would maintain such merchandise at a distance of 3 or 4 feet from
the window.
=79. Fire-Doors and Frames.=—There is no more important feature in
the design of a mill building than the tin-lined fire-doors and their
attachment to the jambs. Every fault in their construction, as viewed
by the Underwriters, is likely to cost the owner additional insurance.
[Illustration: FIG. 37]
[Illustration: FIG. 38]
All tin-lined doors, when one door is used, should be made of three
thicknesses of tongued-and-grooved planking, laid up and down and
horizontally, and clinched-nailed, as illustrated in Fig. 37. The tin
lining on these doors must be of IC tin, put together with locked
seams, secretly nailed, and presenting the appearance designated in
Fig. 38.
=80.= The sills of openings covered with tin-lined doors must always
project under the door, so that there is no danger of burning through
the floor and thus communicating to the space protected by this
entrance. The several constructions of sills most commonly used are
illustrated in Fig. 39.
[Illustration: FIG. 39]
=81.= Sliding-doors should be hung with anti-friction adjustable
hangers. That is, the wheel of the hanger should have roller bearings
for the axle, and there should be some means of adjusting the height
of the door above the threshold by means of the hanger. The track for
sliding-doors should be placed on a slant toward the opening, so that
the door will automatically close. Where it is desired to have the
door open, it may be held back by means of a chord, fusible link, and
counterweight.
=82.= All folding doors should be heavily strap-hinged, and secured to
the jambs with iron-hanging stiles and hinge eyes with through bolts,
as shown at _a_, Fig. 40.
[Illustration: FIG. 40]
Care must always be taken that any through bolts that go through brick
walls near door openings, as the bolts shown at _a_, Fig. 40, be far
enough away from the jambs so that there will be no danger of the bolts
pulling through when put under strain. It is always better to build
these bolts in the wall as the work progresses than to drill holes and
put them in afterwards.