Cast Iron Uprights

are composed of two or more pieces. When of two pieces, they may be connected by flanges and bolts at the centre, where they should have a diameter of about

of the length, and a cross-section determined by the maximum stress, and the power of resistance of the material, as indicated in the table [XCIII.]

The upright may taper from the centre to either end to a diameter of 5 to 6 inches, internally. The lower

upon a seat (e), inside of the upright, upon the connecting block. The strength destroyed by this cutting the post should be restored by additional metal in a band or collar (c, Fig. 37), around the opening, and, if necessary, by the wing flanges d d, extending 6 or 8 inches above the opening. To avoid too much cutting of the post, the flanges of the beams may be reduced to 3 or 3 inches in width. The post and beam seat upon the connecting block may be elevated 3 or 4 inches above the links, as may be required, so as to allow sway rods to pass through with simple screws and nuts for adjustment; thus dispensing with turnbuckles.

Holes should be cast in the central part of the post, for diagonals to pass obliquely through. Or, what is perhaps better, the connecting bolts may be lengthened so as to permit the insertion of an open box, or frame, between the flanges, as seen at a, Fig. 37. This intermediate piece should be so constructed as to close the ends of the hollow pieces meeting it, and prevent the water from getting inside.

The top end of the upright is forked, with concaves for the connecting pin to rest in, as described in the last section, and as seen at a, Fig. 38. The cap piece of the post may be cast separate, or in connection with the upper half of the column. Both plans have been satisfactorily used. All joints, when practicable, should be accurately fitted by turning or planing.

This plan of a cast iron upright, composed of two principal parts, with or without the centre piece, is perhaps as good as any for general use; the principal disadvantage being the difficulty of giving a sufficient diameter in the middle for stiffness, without two much reducing the thickness of metal, or increasing the amount of cross-section beyond the proper theoretical proportions.

To obviate this difficulty, the device adopted in the original model of the Trapezoidal bridge, was that of using truss-rods, or stiffening rods, to secure the post against lateral deflection, after the mannner shown in Fig. 38.

In the case of using stiffening rods for the uprights, it may be recommended to form each half of the column in two pieces, somewhat in the manner above described for the whole one, without stiffeners; making the piece forming the end portion about th shorter

than the other, with a strong flange at the larger end, to afford attachments for the stiffening rods.

FIG. 38.

In Fig. 38, a c d exhibits the upper half of the upright; h, the stretcher at d; k, the flange at c (enlarged), and i, j, enlarged sections of the two ends forming the joint at c. The piece running toward the centre has no flange at c, but hac n inc. ease of thickness for a short distance from the joint, as shown at j, and a diameter about larger than the abutting piece, which latter has a small burr entering the former " or " to keep the ends in place. At, each of the pieces meeting at that point, has a bi-furcation, so as to form an opening for diagonals to pass through, at the same time passing through the stretcher h.

The lower half of the upright is the same as the upper, except the end, which is squared to fit a flat bearing upon the connecting block. An enlarged vertical section of the lower end is shown at 1, Fig. 38. See also Fig. 37, where is shown the arrangement for the beam to enter the opening in the lower part of the upright, as described few pages back.

Floor beams of wood or iron may be suspended below the chords by bolts passing down through the connecting blocks, or, wooden beams may be in two

parts, resting upon flanges cast upon the upright about 3" above the lower end; the beam timbers being hollowed out upon the insides, so as to embrace the upright, in part, leaving a space of 2 or 3 inches between, and secured in place by bolts and separating blocks.

The mode of inserting iron beams by means of openings in the uprights, has already been explained. Lateral ties, or sway-rods may be inserted by bolting to the beams (Figs. 31 and 33), attaching to the inner end of connecting blocks, as at d, Fig. 35, or by passing through the block between the links and the post and beam seat, in the manner referred to two pages back.

Diagonal ties of wrought iron, and transverse struts of wrought or cast iron, are also required between the upper chords, to keep them in line. Cast iron crossstruts may have the web and flange form of section, with shallow sockets at the ends, to admit the connecting bolts at the upper chord to enter, after passing through eyes upon the upper sway-rods and nuts to hold them in place. These sway-rods require turnbuckles for adjustment, when they extend across one panel only. But if the bridge be wide between trusses, the rod may extend only from the end of one crossstrut to the centre of the next, where it may pass through the strut, and receive a nut on the end. Thus, four rods meeting at the centre of the strut, each having its appropriate hole to pass through, all as near to one another as practicable, with sufficient space for nuts to turn (see a and e, Fig. 39), it forms a convenient arrangement for adjusting the rods to a proper tension, at the same time affording lateral steadiness to the cross-strut.

The end-most struts, however, should have no rods connecting with them in the centre, as they can have

no antagonist rods on the opposite sides to prevent the springing of the struts. The end panels should have two full diagonals with turn-buckles, and two half diagonals connecting with the centre of next strut.

In Fig. 39, a shows the middle of the cross-strut, with the upper flange removed; e, a joint of the upper chord, where the connecting bolt passes transversely, receiving eyes of sway-rods, and nut, and entering the end of the strut at d; the upper part of the strut being removed, down to the socket. The bolt bears upon a slight swell in the bottom of the socket, to ensure a central thrust: (see also, b, Fig. 38). At e is presented a side view of the centre of the strut, showing the arrangement of the holes.

A similar device has been used with good effect for giving lateral support to posts or thrust uprights, of the web and flange form, so proportioned as to have greater stiffness transversely than lengthwise of the

truss.

It has been demonstrated that the weight sustained by these posts, increases toward the ends of the truss, while the tension of counter diagonals runs out to nothing, a little way from the centre of the truss. For instance, 4/6 Fig. 18, sustains 6w"-14w', which is a negative quantity whenever w is less than 4w', that is,