Iron Straps. In the framing together of large timbers, in addition to the "joints" we have already illustrated, the parts are secured and kept together by means of iron straps, and by screw bolts and nuts. In fig. 8, Plate LVI, we illustrate a a form of strap for joining the foot a of a king post with the lower part of struts b b; and in fig. 9 a form of strap used for ioining the upper parts of these members. In fig. 12 a more complicated form of strap is illustrated, which, if reversed in position, would answer for the lower part, as in fig. 8. Fig. 10 illustrates a form of strap used to join the head a a of a queen post with the straining cill 6, and head of strut c. Fig. 13 illustrates a form of strap used to connect the head of a strut or brace a with the principal rafter b. Fig. 14 is a form of strap used to connect a collar beam a with rafter b, fig. 11 shows a more complicated form. Fig. 15 illustrates the use of a screw-bolt and nut in connecting the foot of a principal rafter a with the tie beam b; butting pieces or cushions, as c c, of iron should be used to prevent the head of the bolt and nut from entering the wood, the faces of these should be at right angles to the centre line of bolts. In place of a bolt, a strap, as shown by the dotted lines d e, might be used to connect the two pieces a b. Iron straps are provided with screw-nail, or bolt holes, by which they are secured to the timber; in fig. 17 we illustrate a method of enlarging the strap, so as to form an "eye" and butting place, as a, for the screw-bolt head or nut to butt against; c being the edge view of same. In the chapter on Roofs the student will find another method of securing straps by means of "keys" and "gibs."

45. Iron and Timber Combined Work is further illus trated in Roofs and General Framing, some drawings of the great variety of combinations of which we give in Plates LV., LVIII., and LIX. In Plate LV. there are several combinations suitable for "king-post" and "queen-post" roofs, as already illustrated. Thus, fig. 2 shows an arrangement for connecting a wrought-iron "king bolt," or "sus-pending-rod " a, with a cast-iron " box," or " king-post head " b, in which hollow places are made at the sides, in which the ends of the rafters c d are housed; e, the " ridge-piece" or " ridge pole." The upper end of bolt a is finished off with an eye-piece, as at a, fig. 14; this passes between the hollow part of the eye / of box b b, and a pin (as a, fig. 9) is passed through all, and secured by a split key (as b, fig. 9). Fig. 4 shows another method of securing the upper end of bolt a, fig. 2, to the box b b, the bolt being passed up an aperture made in the box, and secured by keys a b passing through slots made in the box and rod. Fig. 3 shows a method of joining foot of king bolt to timber tie beam b, by screw nuts c d, the lower part of the bolt being screwed. In fig. 13 another method is shown; an iron stud a a, with eye b, being bolted to the tie beam; b is the end of king bolt, being secured as shown at a b, fig. 9. Fig. 1 shows part of a roof truss of iron and timber combined, to which the details above explained in figs. 2, 3, 4, and 9 are applicable. In some cases the timber tie beam is dispensed with arid a wrought-iron rod substituted, as at a a, fig. 5 (as a rule, in combinations of wood with iron, those parts in tension (see remarks on strains in a succeeding chapter) may be of wrought-iron, those in compresssion, of timber or of cast-iron. Fig. 6 shows the detail of junction of tie rod a a, feet of braces or struts b b, foot of king bolt b, with the cast-iron shoe or box d d, in. which the feet of the braces c c are housed; the lower part e e is made double or hollow, to admit of the tie rod lying in it, this being provided with an eye, through which the king bolt end passes; or if the king bolt is secured by a key, as at /, the tie rod may be left plain. The other end of the tie rod may be jointed to an eye - as shown by the dotted lines c, fig. 7 - made at a, in the rafter, shoe, or box b b, which receives the feet of the rafters b b, fig. 5, or secured to the rafters by a jointed link c.

Figs. 8 and 9, Plate LV., show three methods of joining the wrought-iron " queen bolts " a a - substituted for timber - with the straining piece b b, c c being the end of a "principal rafter." In fig. 8, c is tenoned into b, and the " queen bolt" is simply passed through a hole in the piece b, and secured by nut at the upper and screwed end. A stronger method is shown in fig. 8 at e e, which is a strap embracing the piece b, and secured by a pin and split key passing through the eye f ; this is shown in section in fig. 9. In fig. 10 a cast-iron box or shoe a a is made, in which the ends of the pieces b and c are housed, the king bolt d being secured by a nut e at top, and by a "jamb-nut " at /. Fig. 11 shows a method of securing the foot of the " queen bolt " a - corresponding to a, fig. 8, d, fig. 10 - with the tie beam b b, c d being the foot of brace or strut, housed in the cast-iron shoe d d, bolted to the tie beam, b b; the queen bolt a may be used as one of the bolts. Fig. 12 illustrates a method in which a second queen bolt a - as a, fig. 1, Plate LVIII. - may be joined to the cast-iron box b b, in which is housed the ends of the principal rafter c c, the strut or brace d, and the purlin e.

An illustration of a railway shed is given in Plate LVIL, in which wood is combined with iron. The sides of this shed are open from the ground line e e, fig. 1, to the under side of the longitudinal timber bearer f f, and fitted in above this with the cross-pieces g g, and the boarding h h. On the upper beam or bearer i i rests the cast-iron beam j j, cast with open circles, as shown; above this is the timber bearer k k, to which the rafter boxes l of the wrought-iron roof are secured. Fig. 2 is section on the line a b, fig. 1; and fig. 3 a sectional elevation, showing relation of the timbers and pillar, or column, in fig. 1; fig. 4 is side elevation of fig. 3; fig. 5, horizontal section on the line a b, fig. 4; fig. 6, inside view of the column or pillar at lower cap or shoe d, fig. 1; fig. 388 is side elevation of do.

The scale for fig. 1, Plate LVIL, is inch = 1 foot; for details, one-twelfth full size or one inch to the foot. In Plate LX., fig, 11, we show an arrangement for carrying a girder of wood a a, on the cap b, of a cast-iron column c, the girder being secured to cap by a screw bolt and nut, as shown. The drawing also illustrates a method of crossing an opening, as that of a shop front, by the built wrought-iron beams d d, supported at each end by cast-iron columns c, and the upper plate, as e e, carrying the wall / of upper storey. The built beams, as d d, are secured at intervals by bolts, as g. Should these beams d d be required to carry timber or other beams on their flanges, these will rest on and be secured to the lower plate of d d.

44 Iron Straps 215

Fig. 388.