RAILWAY CONSTRUCTION. 135 



iron, and are held together and to gauge by tie-rods, as shown. 

 The rails are spiked or bolted down on to the timber beams, and 

 the flooring formed of strong planking. 



Fig. 133 shows an arrangement of plate girders for a 16-foot 

 opening over a stream. The girders are placed immediately 

 under the rails, and are tied together by plate-iron cross- 

 bracing the same depth as the main girders. The flooring con- 

 sists of 4-inch planking laid with f-inch spaces, on which are laid 

 longitudinal rail-bearers 14 inches wide by 7 inches thick. 



Fig. 134 is a sketch of a somewhat similar arrangement for a 

 lattice-girder bridge, 45 feet span, carrying a single line of rail- 

 way over a river. The main girders are tied together by lattice- 

 work cross-bracing. The floorway consists of 5 -inch planking, 

 laid with f-inch spaces, on which is placed the 14 feet by 7 feet 

 longitudinal rail-bearers. Plate-iron outside brackets are riveted 

 to the main girders to carry the ends of the planking and 

 light tube-iron parapet. 



Fig. 135 illustrates an example of trough girders, constructed 

 to carry a double-line railway over a country road 25 feet wide, 

 where the space from under side of girder to rail-level is small. 

 The girders are constructed in pairs, with short, shallow cross- 

 girders at 3 feet 6 inch centres, riveted in between them to 

 carry longitudinal timbers on which the rails are laid. Bottom 

 plates, f inch thick, unite the two girders for the length of 

 their bearing on the abutments, and a similar plate, 9 inches 

 wide, unites them at the centre ; the remainder of the span is left 

 open to prevent the lodgment of rain-water. Three strong tie- 

 rods are placed to keep the girders to gauge. Curved wrought- 

 iron ballast-plates are used between the running-rails, and plank 

 flooring forms the rest of the covering. 



Fig. 136 is a sketch of a plate-girder bridge over a country 

 road 28 feet wide, with the load carried on the lower flange 

 of girder. Three main girders carry the double line of railway, 

 the centre one having double the strength of each of the outside 

 girders. On the top of the cross-girders, strong angle irons are 

 riveted to serve as guides and supports for the longitudinal 

 timbers which carry the rails. Every third cross-girder has 

 raised ends to give increased lateral stability to the main girders. 

 A close cast-iron plate parapet forms a screen to the roadway. 

 Wrought-iron ballast-plates are used between the running-rails, 

 and the remainder of the flooring is of timber. 



