=43.= There is a type of building which, while not distinctly mill
construction as usually understood, is frequently used for one-story
buildings, such as rolling mills, cement works, machine shops,
foundries, rail yards, and buildings of this class.
The essential feature of these buildings is a steel-roof truss
supported on steel columns, the columns being braced both to the truss
and longitudinally of the building. It is usually the purpose in the
design of such buildings to neglect everything but the necessary
stability and the first cost. The steelwork, consequently, is of the
lightest possible construction, usually designed for a unit fiber
stress of from 18,000 to 20,000 pounds, and the covering of the sides
of the building, together with window details, etc., is made only
sufficiently good to keep out the weather.
=44. Material for Roof Covering.=—The roof covering of this class of
building is either of slag on 2-inch spruce plank, spiked to nailing
strips bolted on to steel purlins from beneath, with lagscrews, or of
slate laid on 1-inch or 2-inch sheathing boards. Even galvanized iron
is used for the roofing of some of the cheapest class of buildings,
especially those which, owing to the process of manufacture, are
subjected to a high temperature.
=45. Construction of Sides of Building.=—The sides of these buildings
may be covered with either expanded-metal lath on metallic furring
strips, plastered inside and out with cement mortar so as to form
a fireproof and rigid screen wall about 2 inches in thickness; or,
the walls may be 9-inch or 13-inch brick walls built part way up the
height of the columns and leaving the columns exposed on the face;
or, corrugated galvanized iron lapped 6 inches and secured either by
riveting to metallic supports or nailed to wooden studding secured to
the steel frames. Of these constructions, probably the first is the
most expensive and also the most satisfactory.
[Illustration: FIG. 21]
=46. Partially Supported Steel-Frame Building.=— In Fig. 21, there is
designated a type of construction that may be built for about $1 per
square foot of the area covered. This consists of steel =I= beams, or
angle-and-plate columns, used for column supports carrying the usual
angle iron steel-roof truss. The roof is sheathed with 2-inch spruce
tongued-and-grooved planking, covered with a good quality of roofing
felt and slag, with a stop-gutter _a_ at the edge. Owing to the fact
that the steel columns are supported in a direction of their minimum
radius of gyration by means of the brick walls, they can be made very
light. The building illustrated has what is known as a _saw-tooth
roof_. By this means, light is obtained on the side next to an adjacent
and higher building by means of a sash _b_. This sash is usually made
hinged or pivoted, to provide the necessary ventilation.
=47.= In Fig. 22, there is illustrated, diagrammatically, the framework
of a one-story skeleton-construction building. In the design of all
such buildings, where there are no end gable walls, the several
columns and trusses must be braced diagonally, as indicated at _a_,
_a_, and frequently it is necessary to introduce a secondary system of
horizontal bracing from one panel point on the lower chord to another,
as indicated at _b_, _b_.
[Illustration: FIG. 22]
In placing galvanized ironwork on the sides of steel-mill buildings,
it is best to construct the necessary framework between the main
supporting members of the building of light angles, or tees. These
should be furnished punched with ⅜-inch or ⁵/₁₆-inch holes, to
which the galvanized iron may be riveted, it being best to mark the
galvanized iron in the field and punch it there. This may be done
without much difficulty with the usual light gauge used for this
purpose. It is sometimes necessary with this construction to flash
around the window and door heads with IX tin.