RAILWAY CONSTRUCTION. 139 



Fig. 141 shows cross-section of a plate-girder bridge, of 36 

 feet span, carrying six lines of way across a street. Strong 

 plated cross-girder bracing, at 4 feet 8 inch centres, is riveted 

 to the main girders, and the top is covered with old Barlow rails, 

 12 inches wide, and weighing 901bs. per lineal yard. A layer of 

 asphalte, about 1 inches thick, is carefully laid all over the 

 upper surface of these rails to make a thoroughly water-tight 

 floor. Clean gravel is placed on the top, on which are laid the 

 sleepers and rails of the permanent way. Rain-water passes 

 through the gravel into the hollows of the Barlow rails, and finds 

 its way into suitable drains provided at each abutment. This 

 arrangement not only prevents the falling of drip-water into the 

 street below, but permits of the alterations of the lines of way, 

 or putting in of cross-over roads on the surface above. The out- 

 side main girders are made deeper, and are surmounted by close 

 cast-iron parapets. 



Fig. 142 gives the particulars of a three-span plate-girder 

 bridge, constructed to carry a double line of railway over two 

 other railways and a canal, the load being placed on the lower 

 flange. Two main girders are used for each line of way. Strong 

 plated cross-girders are placed at 5 feet 3 inch centres, and on the 

 top of these is laid a flooring of old Barlow rails, terminating at 

 the sides with sloping wing-plates riveted to the cross-girders 

 and main girders, the entire surface being covered with an inch 

 and a half layer of asphalte. Good gravel ballast is placed on 

 the top, on which are laid the sleepers and rails. One central 

 main girder of sufficient strength would have been as efficient as 

 the two central girders, but there was a practical difficulty 

 which prevented its adoption. The new girder-work was built 

 to replace an old structure of peculiar arrangement, and to keep 

 the traffic going on one line there was no alternative but to 

 make each line of way complete in itself. 



Fig. 143 illustrates an example of jack arches in concrete 

 built between strong plate-girders. The span of the girders was 

 only 16 feet, but the opening or roadway was of considerable 

 length, and passed under a portion of a busy station yard. The 

 girders are placed at 6-foot centres, and tied together in pairs by 

 1^-inch tie-rods, three to the span, spaces of ^6 inches in plan 

 being allowed between each set of the rods. The concrete was 

 curved up to the top plate of the girder, as shown, and the entire 

 surface covered with a thick layer of asphalte, on which were 



