The section of rail employed is usually either a bridge rail, as in Fig. 245, or a flat-footed rail, as in Figs. 59, 60, 61, 62, 63. The former section has possibly greater stability under the lateral shocks which may occur; the latter section has some advantage in the greater facilities which the bottom flange offers for connection to the supporting girder. In contractors' plant, such as goliahs or titans for temporary work, the rail is very frequently riveted down to the upper flange of the supporting girder, and may in such cases be considered as a portion of the total effective section of such flange, when no joints occur in the rail at critical points in the bending-moment curve.

Where, however, it is considered desirable to retain the facility of renewing the rail without interference with the structure of the girder, another form of fastening must be adopted in lieu of rivets.

Fig. 59. Scale 1½ inch = 1 foot.

Fig. 60. Scale 1½ inch = 1 foot.

A convenient form of such a connection is shown in Figs. 59 and 60, and is repeated under slightly varying conditions in Figs. 61, 62, 63, 64.

It consists of a clip, which may be of cast iron or shaped in mild steel, of a form to suit the exact outline of the rail used, and of length sufficient to enable a bolt to be used which can be properly spaced so as to pass through the flange plate and angles of the single-webbed girder used in this case.

Fig. 61. Scale ¾ inch = 1 foot.

In Fig. 64 the bolt is tee-headed so as to clear the edge of the flange of the rolled joist. In Fig. 63, where the section of the traveller girder is the rolled joist without any additional flange plates, the bolt is so spaced as to pass through the joist flange, with as much metal outside the hole as can be obtained, while the edge of the rail flange is notched to receive the bolt. Were it always possible to obtain a section of rail having just that amount of foot which the designer would prefer for his connection, the design would often be simplified. Unfortunately, from the designer's point of view, it frequently happens in rail sections, when applied to work of this kind, that only that section can be adopted which is commercially obtainable at the moment.

Fig. 62. Scale ¾ inch = 1 foot.

Fig. 63. Fig. 64. Scale ¾ inch = 1 foot. Scale ¾ inch = 1 foot.

In Fig. 245 the bridge section of rail shown is secured to the timber (elm) bearer by coach screws, an iron flat, 9" X ⅜", being placed under the rail to increase the bearing and lessen the indenting stress upon the timber under the rolling load.

Returning to the consideration of the type, sections, and details of the traveller girders themselves, we have in the illustrations appended a few of the methods of construction in frequent use.

An example of the fish-bellied single-webbed plate girder is given in elevation in Fig. 216, and in section in Figs. 65, 66, Fig. 65 being a section at end, and Fig. 66 a section at centre of girder. The section at the centre of a pair of these girders is given in Fig. 67. It will be observed in this example that opportunity is taken in the contiguity of the pair of girders to secure additional lateral stiffness, under accidental shocks from the crane, by means of the pair of struts formed of 3" x 3" X ½" angles bolted on to the plate stiffeners of the main girders.

Fig. 65. Scale ¾ inch = 1 foot.

Fig. 66. Scale ¾ inch = 1 foot.

The bolted connection, combined with sufficient play in the bolt-holes, enables the pair of stiffening bars to act in some degree as a parallel ruler whenever either of the traveller girders is slightly deflected below the level of its neighbour by a rolling load. The advantages of the adoption of a fish-bellied form as regards practical uniformity of section of the top flange, and a consequent simplifying of the rail connections, has already been dwelt upon. The construction is a little more troublesome in manufacture, owing to the necessity of shearing the web plates to the curved outline, and the bending of the main angles in the bottom flange, but the extra cost is not very considerable.

Fig. 67. Scale ¾ inch = 1 foot.

Fig. 68. Scale 1½ inch = 1 foot.

Fig. 69. Scale ¾ inch = 1 foot.

Fig. 70. Scale ¾ inch = 1 foot.

It may be remarked in passing that great stiffness or freedom from excessive deflection is frequently of considerable practical advantage in those cases where shafting is attached, as it often is, to traveller girders by means of bracketing, and where any considerable amount of deflection would be detrimental to the action of the shaft. Fig. 68 is a sectional plan at the end of one of the girders showing the seating on the column. The end elevation of the girder, showing the end plate and the bolted connection with the next abutting girder, is shown in Fig. 69, while Figs. 70, 71 show the same detail in side elevation. The joint in the rail is over the joint in the girder, and is covered by a fish-plate in the usual way, allowance being made for expansion. As the joint between two adjacent girders is over a rigid support, there would not appear to be any substantial advantage in this case in making the rail joint to break joint with the girder joint, although cases might arise where such a course would be judicious.