RAILWAY CONSTRUCTION. 147 



not to be recommended where iron or steel plate troughing can 

 be obtained at a moderate price. 



Fig. 152 gives cross-section of plate-girder over-line bridge, 

 41 feet 6 inch span, carrying a public road, 25 feet wide, over 

 three lines of way. Two main girders are used, of sufficient 

 depth to form parapets or screens for the finished roadway. 

 Plate cross-girders, placed at 6 feet 6 inch centres, are riveted 

 to the web-plate and lower angle irons of main girders ; and on 

 these is placed a flooring of plate-iron longitudinal troughing 

 to carry the metalled roadway. 



Fig. 153 gives the particulars of a plate-girder over-line 

 bridge, carrying an important public road, 35 feet wide, over 

 several main lines and sidings. The carriage-way is carried by 

 two girders placed at 25-foot centres, and on the lower boom 

 of these are riveted lattice-work cross-girders to receive the 

 plate-iron longitudinal troughing and roadway. The footpath 

 girders are set at a higher level, and the load placed on the 

 lower flange. The curved side brackets merely act as bracing 

 between the carriage-way girders and footpath girders. A cast- 

 iron-plate parapet is bolted on to the top of each of the footpath 

 girders, making a close screen, 6 feet high, above the footpath. 

 Lattice-work cross-girders were adopted for the convenience of 

 supporting small water mains and gas mains below the road- 

 level. The roadway is formed of ordinary metalling, and the 

 footpaths of asphalte pavement ; the kerbing is of granite, and 

 the side water-tables of crushed granite concrete. 



Fig. 154 is a cross-section of a small uncovered lattice- 

 girder footbridge 41 feet span, and 5 feet wide, suitable for 

 small roadside stations. The top and bottom flange consist 

 each of two angle irons, those in the bottom flange being placed 

 table side upwards, so as to bring the entire section of both angle 

 irons fairly into play, and also to provide a better bearing for 

 the channel-iron cross-girders which carry the planking of the 

 footway. When planking is carried on the inside of light angle 

 iron, as in Fig. 155, a severe strain is produced at the point A ; 

 this is entirely obviated by placing the bottom angle irons table 

 side upwards, as in Fig. 156. Three of the channel-iron cross- 

 girders are extended outwards, and to the ends of these are 

 riveted tee-iron stiffeners to steady the main girders. In some 

 cases stamped, or ribbed, wrought-iron plates are used for a 

 footway, but, although more durable, they do not give such a 



