=30.= A type of factory construction more usual than that previously
described is illustrated in Fig. 12. In this illustration, it will be
noticed that the main girders bear on wall pilasters, and the spandrel
filling between the pilasters is kept as thin as possible. The usual
reveal window frame is used, as shown at _a_, and the soffit of the
arch over the window openings is checked at the head of the opening to
provide a wind and water stop as at _b_. In this construction, which
is probably the best, though it does not possess the advantage of
giving the maximum amount of window space, and, consequently, light in
the building, a rowlock or bonded brick arch is used over the window
frames. By means of this construction, either the window frame may be
built in place, or the windows may be slipped in from the back against
a rabbet formed in the brickwork. The arch over the window head is
indicated at _c_.
[Illustration: FIG. 12]
[Illustration: FIG. 13]
=31. Floor Construction.=—The floor construction consists of
heavy timber girders, no dimension of which may be less than 6
inches, as otherwise it would not comply with the requirements of
slow-burning construction. The floor planking consists of 3- or 4-inch
tongued-and-grooved spruce, or yellow-pine planking, planed on the
under side, and thoroughly spiked to the girder. Planking of the
former thickness may be used for clear spans as great as 8 feet, while
the latter thickness may be used for up to 10-foot or even 12-foot
spans, if the loads are light. The girders are indicated at _d_, and
the floor planking at _e_. Usually the girders, in order to obtain the
requisite strength, are made of long-leaf yellow pine. On the top of
the spruce planking is placed a finished maple floor. This floor is
made from either 1-inch maple, which finishes as ⅞ inch, or 1¼-inch
maple, which finishes as 1⅛ inches, in thickness. Neponsett sheathing
paper, or deadening felt, is placed between the spruce planking and
the finished maple flooring for the purpose of preventing dust from
percolating through. This sheathing paper or felt is sometimes made
waterproof to prevent leakage due to water used for fire-extinguishing
purposes.
Frequently, the brickwork is corbeled out, as indicated at _f_, in
order to form a fire-stop between floors, or at least to prevent an
open joint at this place. Where the walls are offsetted, as shown in
Fig. 13, there is no need of corbeling out, for the offset in the
brickwork can be made to form the fire or dust stop.
=32.= Where heavy yellow-pine girders bear on brick walls, it is
usual to obtain the requisite bearing area by the use of cast-iron
bearing plates, as indicated in Fig. 14 (_a_), (_b_), and (_c_). In
(_a_) is shown an ordinary flat plate that has an area figured so that
the load on the brickwork will not exceed its ultimate stress, which
for brickwork laid in lime-and-cement mortar is about 150 pounds per
square inch, while for brickwork laid in cement mortar, it is in the
neighborhood of 200 pounds per square inch. This plate is usually cast
with a lug on the back, as at _a_, to be built in the brickwork, and
dowel-pins, or a lip, as at _b_, over which the girder is fitted,
or notched. By this means, a tie to the wall is obtained. There is
difficulty, however, in using such a connection, for the carpenters on
the job frequently miscut their beams, so that the notchings or borings
at _b_ do not come where they should, and to remedy the defect, the
notchings, or borings, are cut or gouged out, so that frequently the
pin or lip at _b_ is not brought to bear against the timber.
[Illustration: (_a_)]
[Illustration: (_b_)]
[Illustration: (_c_)