which the ends of the rod, c c, are bolted, as also the end of the rod, d, corresponding to bf, fig. 150. In fig. 8, Plate XVIII., we give the front elevation, showing the junction of the upper ends of rafters of the truss to the right hand of fig. 150, at point d, with the upper end of tie bolt, c d. In this arrangement, the cast-iron rafter box, as shown in fig. 7, Plate XVII., is dispensed with, and the rafters, a a, b b, fig. 8, Plate XVIII., are secured together by two plates of wrought iron, one on each side, as, c c c c, the whole

being bolted together the ends of the rafters butting

together with a plain or

butt

joint. The tie bolt, d d, is eyed out at its upper extremity, and embraces the two plates and the rafter, as shown in the section in fig. 5, Plate XIX. The ridge pole, or piece, e e, fig. 8, Plate XVIII.,

is notched into the block of timber, ff, secured between the angle irons rivetted to the flange of the rafter; h h, the roofing boards. The rafter box at foot of rafters is shown in elevation at fig. 6, Plate XIX; a a, the wall; bb, the cast-iron rafter box, provided with a recess in front to receive the end of rafter, c c, and which is secured by a bolt passing through the bolt hole, d; e, the end of the clip of tie bolt, the eye of which is secured by a bolt passing through the bolt hole, f. A

sectional plan of this in its full length (fig. 6, Plate XIX., being too small to admit of its being given there), is given in fig. 6, Plate XVIII. ; a side elevation in fig. 5. In fig. 6, a a is the end of the bolt; this is embraced by the clip, bb (bb, fig. 5, in side elevation), which is secured to the rafter, cc, by the pin or bolt, d, passing through the bolt hole, f, fig. 6, Plate XIX.; this pin or bolt is kept in place by the split pins, e e; fis part of the rafter box corresponding to b b, fig. 6, Plate XIX., secured by the bolt, g, passing through the bolt hole, d, fig. 6, Plate XIX. In fig. 6, Plate XVIII., filling-in or bolster pieces, h h, are placed at side of rafter to make up

the space; the clip, b b, and end of tie rod, a, fig. 6, Plate XVIII., are secured together by the "gibs," i i, jj, and cottar, k k; an inside edge view of one of the gibs being shown at fig. 7, Plate XVIII. In fig. 2, Plate XIX., we give a side elevation at a, fig. 150, showing method of joining the upper end of strut or brace, c a, with rafter, de, and queen bolt, a b. In fig. 2, Plate XIX., a a is rafter; b, end of strut, secured to the rafter by plates at each side, one of which is shown at c c; the upper end of queen bolt, dd, is secured to the plate, c, and rafter, a,

by a bolt passing through the bolt hole, e. Fig. 1 is a side elevation and section of the arrangement taken through the line, a'b', in fig. 2. In fig. 3, side elevation of the arrangement of parts at the point b, fig. 150, is shown-a a, the lower end of strut or brace, b, fig. 150; b, the lower end of queen bolt, d, in fig. 2, Plate XIX., this passing through the end of flange, c, of brace or strut, a, and the eye, d, of tie bolt, e e (corresponding to ce in fig. 150), and as shown in plan, fig. 4, Plate XIX. The flange of the strut or brace is shown to be uppermost, as in the arrangement usually adopted, although in some cases the flange is placed on the lowest side, as in

fig. 1, Plate XVII., at gh. In rafters the flange is always placed uppermost, as shown in fig. 10, Plate XVII., fig. 8, Plate XVIII., and fig. 6, Plate XIX. In fig. 152, we give at A a section, and in B a side elevation, of a wrought-iron rafter of the form used in iron roofs, the drawing showing in full size a section adapted to a roof of 18 to 20 feet span. The arrangement of the parts at c, fig. 150 will be very similar to that illustrated in Plate XVII., fig. 1. The arrangement of the parts at ƒ and g, fig. 150, similar to those illustrated in Plate XIX., figs. 1, 2, 3, and 4. In fig. 5, Plate XVII., a form of

gutter of cast iron adapted to an iron roof is shown; and in fig. 7, same plate, a wrought-iron or zinc one, this being riveted to the end of the flange of the rafter, a, prolonged for this purpose beyond the line of rafter box, b, and wall, c. Other arrangements

of roofs and details the reader will find in the Advanced Course of Building Construction in this series.

d

37. Iron Beams.-As substitutes for those of timber, beams are made of cast and wrought iron, and of various forms, the best for cast iron being that illustrated in fig. 153; in this the area of the section of upper flange, cd, is one sixth that of the lower flange, a b; ef, depth of beam over all; c d, width of upper flange; i, thickness of upper flange; a b, width of lower flange; g h, thickness of lower flange; k, thickness of rib. In the Advanced Handbook of

Fig. 154.

Fig. 155. Fig. 156. Building Construction, the reader will find a resumé of the peculiarities of cast iron as a building material, and of the reasons why-where the safest and best method of construction is considered-beams of that material should

be discarded in favour of wrought iron, the peculiarities of which will also be described.

The scope of the present work admitting only of

a

с

b

Fig. 157.

a

general illustrations of form being given, the reader must refer to the same work-above namedfor a description of the "strains" to which iron and timber are subjected, and for the principles upon which beams and framework of these materials are designed, to meet the requirements of various positions and localities.

Beams of wrought-iron, as now used in practical construction, are of three classes-1st, Solid Rolled, as in fig. 154, a, b, and c, these being used for small spans, and for buildings where comparatively light

ΠΙ

Fig. 158.

Fig. 159. weights are to be carried, or small pressure sustained. 2nd, Built Beams (solid), as in figs. 155, 156. 3rd, Built Beams, open or hollow, or, as they are generally