Iron Roofs. In the Elementary Volume on Timber and Iron, the student will find illustrations of forms of roofs, as the " king-post" roof, which may be considered as supplementary to what we now purpose to give. In Plate LVIII. we give, in fig. 1, the outline of a shed roof, which may also be adapted to the shed illustrated in Plate LVII. The lines b b represent the pillars or columns placed at intervals along the sides to any desired length, the spaces between these being 17 feet. They support or carry cast-iron beams a a, as shown in elevation in fig. 5, and in plan, fig. 6, or open beams, as in fig. 397, may be substituted. The ends of these beams are provided with projecting parts which go into slots made in the upper part of the pillar b b, fig. 5, or a a, fig. 4, or they may be secured as shown in figs. 4 and 5, Plate LVII., which is a somewhat similar arrangement. The beams a a, fig. 5, Plate LVIII, carry at 8 or 10 feet intervals, cast-iron shoes or rafter boxes which receive the ends of the rafters of the truss of roof shown in full lines, fig. 1. Fig. 2 is base of pillar or column, the part A A being hexagonal as in fig. 3 plan, fig. 4 is the cap of column, fig. 9 shows the junction of principal rafter c c, with cast-iron shoe or box, and the end of the rod d d, keyed into the shoe. Pig. 8 shows another method of joining end of tie rod d d, fig. I, a a, figs. 7 and 8, with the rafter b b, by means of a link c c, secured by bolt and nut d e passing through the eye at its termination. In fig. 4, Plate LVI., we show the method of securing the upper end of the rods f f, fig. 1, Plate LVIII, with the principal rafters c c. In fig. 4, Plate LVI, a b are the ends of the two rafters, butting against each other, and secured by a "junction plate" c of wrought-iron, one on each side, the bolts which pass through the eyes e e of the links d d, at the upper end of the rods, keeping the whole together. Pig. 3, Plate LVI, is the lower end of the " angle-iron" strut or brace e e, fig. 1, Plate LVIII joining the tie rod d d, fig. 1. The tie rod a a, fig. 3, Plate LVI, is widened out at b b to receive the returned or bent end c c of the strut or brace d; the whole being secured by bolt and nut. The lower end of the rod/, fig. 1, Plate LVIII, is secured to the strut d, fig. 3, Plate LVI, as shown, or a double link as in fig. 7, Plate
LVIII., may embrace the flange of strut d. Fig. 5, Plate LVI, is the junction of upper end of the strut or brace e, fig. 1, Plate LVIII., with the rafter c c; in fig. 5, Plate LVI, a is the brace, b b the rafter, c c the covering plate of iron secured by bolts and nuts, or by rivets passing through the holes drilled as shown. In some roofs of this kind, the strut e e, fig. 1, Plate LVIII., is made of cast-iron, as in fig. 6, Plate LVI, a a the upper part is cast with a recess, into which the rafter rib d passes, and is secured by bolts or rivets. The web b b of a cross section, as at c c, is terminated by a circular part c c'\ the ends of the "tie rod " (see d d, fig. 1, Plate LVIII.) d d, and of "suspending rod" e, are either dovetailed in to the circular part c c of strut, fig. 6, Plate LVI, as at //, and then covered with covers bolted together; or the ends of the rods may be provided with eyes as at g; the bolts pass through the holes as shown, securing the two covers and the ends of the rod to the central part c' c'. The arrangement or combination of parts in fig. 6, Plate LVI, is that at g, fig. 1, Plate LVIII, In fig. 1, Plate LVI, we give end view of the rafter box of fig. 1, Plate LVIII., a being the aperture into which end of tie rod is passed, 6 slot for rib of rafter, c c flange of rafter; fig. 2, Plate LVI, is plan of rafter box. In Plate LIX. we give drawings illustrative of the principal parts of a railway platform, for a small way-side station roof. In fig. 1, a a is surface of platform, b b wall of station-house, c c the pillars or columns carrying the cast-iron beams or ornamented girders d d, which are secured to the upper part e e of pillars in the manner shown in fig. 4, sectional plan, and fig. 5 part elevation, or by the alternative method in fig. 6 sectional plan, and fig. 9 part elevation. These beams d d run at right angles to the railway, and at right angles to them, or parallel to the railway, and secured to the part e e of pillar in fig. 1, as shown in figs. 4 and 5, or figs. 6 and 9, are the ornamental beams f f , fig. 2, which are placed next the railway at the end f, fig. 1, and form the outside "principal rafter." The other principal rafters are placed at intervals between the point f and wall b b, fig. 1; being constructed with "T "-irons placed back to back as shown in section 405, while between the " principai rafters" the common rafters are placed, as at fig. 3, which gives the form of truss for both rafters. The ends of the rafters are secured to cast-iron gutters, which go into recesses at e e, fig. 2, or are bolted to the flat surface if no recesses are provided. This gutter, which runs parallel to the beams d d in fig. 1, is shown in fig. 409; in which a a a is the gutter, b b the rib of the two rafters, and bolted together at e ; the flange c c of rafter being secured to the cast-iron gutter side flanges by bolts and nuts d d. This form of gutter may be used for a "ridge and valley" roof, the inner ends of the principal rafters of which rest upon a central wall, or upon beams supported by pillars, the gutter being secured to wall or cap of pillar by the bolts and nuts f f, fig. 409. Figs. 1, 2, and 3, Plate LIX., are drawn to a scale of ¼" = 1 foot; the details, and also fig. 409, are one-fourth full size. Fig. 7 is section on line a b, fig. 2; fig. 4 on line c d; fig. 8 is the outside single gutter which terminates the roof, and is secured to the last beam f f, fig. 1. In fig. 16, Plate LVI, and in fig. 410, other forms of gutters are illustrated; and in the next division, other forms adapted to zinc roof coverings will be shown. Fig. 410 shows a "double gutter" adapted to a " ridge and valley " roof, made of wrought-iron in place of cast-iron, as in fig. 409, and supported by a built beam a a, b b the right and left hand rafters of the two roofs, c c the gutter.
51. Iron Roof Trusses are of various combinations, some of these we have already illustrated; we give in figs 411 to 416, inclusive, diagrams showing other combinations; fig. 412 is a queen-post truss with eight bays, adapted for a fifty feet span, the principals, as in the diagram, are to be placed not less than seven, and not more than eight feet apart. The dimensions are as follows: - "tie rod" a a 1⅜" diameter; rafter b b " T " iron, 3½" x 3½" x ½" rib; " suspension rod," or "queen bolt," c ½ d, do., d ½", do., e ¾", do., f ⅞"; strut or brace g "angle-iron" 2½ x 2½" x ⅜", do., h 3" x 3" x ⅜"; the
"rafter" of the "louvre ventilator," j 3½" x 3½" x ½" "tie rod " k½" diameter. The ventilator to be covered with inch boarding and zinc, the sides louvre-boarded. The truss in fig. 415 is that of one for a span of between 85 and 95 feet; the "tie" rod b is 2½" diameter; "tie rod" c 2⅜", do. d 2f", do. e 1¾"; the "tie"f 1", do. g 1", h 1⅛, i 1⅜", j 1⅜, k 1⅛, l and m 1", n 1¾", o 1⅝", p 1⅜", q q ⅛". The rafters r r are of two angle-irons 4" x 4½" x ½". The diagrams A, B, C, and D, fig. 416, show various trusses for curved roofs; E an open beam truss. In fig. 15, Plate LV., we illustrate the segmental arched roof of the water-works at Marley, near Paris, the upper curved rib a a being trellis work, as at D, fig. 416; the lower beam b b of form somewhat to that at j, fig. 1, Plate LVII. In Plate LX. we give various illustrations of iron bridge work. Bridges of short span, and not requiring to be loaded with heavy weights, may be simply formed with beams of one or other of the various forms we have illustrated; the illustrations in Plate LX. refer chiefly to railway bridges, and are given with the view to illustrate some of the leading methods of joining iron plates together in work of this kind. In fig. 3, BB and C C D D is the main girder of a "box beam" bridge stretching across the opening; this carrying the cross girder 11, fig. 4, on which the rails are supported, these resting upon the wood bearers J J„ Fig. 2 is a section on the line ab of the cross girder 11, fig. 4, Fig. 5 is the top part, fig. 8 the bottom part, of a " built beam" bridge; figs. 1 and 6, do., and fig. 8 side elevation of fig. 1. In fig. 5, d d is the central plate or web of the beam, with its upper plates - in this case they are curved in outline - a b c secured to the web by the angle-irons e e, f f strengthening vertical plate. Fig. 7 is side elevation, with corresponding letters, a strengthening plate g is placed at intervals across the top plates. In fig. 8 a method of connecting the cross girders, corresponding to the cross girder I J in fig. 4, is shown, a a the web of the main girder, with bottom plates b c d and angle-irons e e; f f are vertical strengthening angle-irons ', g g h the cross girder resting upon the bottom plates b c d. In fig. 6 the section of this cross girder is shown, in which a a are the angle-irons corresponding to g g in fig. 8, b the web to h in fig. 8. Fig. 6 illustrates the cross girder carrying timber bearers c d. Fig. 416a illustrates a form of iron trussed gate, fig. 416b a trussed iron foot-bridge.