RAILWAY CONSTRUCTION. 137 



Fig. 137 gives the particulars of one 60-foot span of a viaduct 

 carrying a double line of railway over tidal water. The main 

 girders are placed one under each line of rails, and all the four 

 are strongly tied together by lattice-work bracing the full depth 

 of the girders. The outside footpaths for the platelayers are 

 carried on strong brackets, riveted to the main girders. Longi- 

 tudinal timbers, coped with angle iron, are placed as outside 

 guards, alongside each rail, for the full length of the viaduct. 

 Wrought-iron ballast-plates are placed between the running-rails. 

 The remainder of the footways consist of timber planking, laid 

 with half -inch spaces, and covered with a layer of small pebbles 

 as a protection against fire. 



Fig. 138 shows a very similar arrangement in a viaduct 

 carrying a single line of railway across a river. The two main 

 lattice girders 66 feet span are placed at 9-foot centres, to 

 obtain greater stability. The cross-girders are extended to carry 

 the outside footpaths and handrailing. Outside guards are 

 placed alongside each rail as in the preceding example. Wrought- 

 iron ballast-plates are fixed all along between the running- 

 rails, and timber planking used for the rest of the floorway. 



Fig. 139 gives cross-section of a lattice-girder bridge, 82 

 feet span, carrying a single line of railway over a river, with 

 the load carried on the lower flange. The cross-girders are 

 placed at 4 feet 3 inch centres. Wrought-iron ballast-plates 

 compose the floorway between the rails, and timber planking 

 covers the rest of the bridge. Plate diaphragms, or stiffeners, 

 of the form shown at A. A> A, A, are riveted to the main girders 

 at five places in their length. 



Fig. 140 shows cross-section of a lattice-girder bridge of 200 

 feet span, carrying a single line of railway over a river, the load 

 being placed on the lower flange. The floorway consists of 

 plate-iron cross-girders, spaced at 4-foot centres, on which are 

 placed the longitudinal rail-bearers and planking, the latter 

 being covered with a layer of clean pebbles for the width 

 between the running-rails. As the depth of the main girders 

 was sufficient to admit of overhead bracing, strong plate-iron 

 diaphragms, of the form shown on the sketch, were riveted to 

 the main girders at every 50 feet. These diaphragms thoroughly 

 brace the two girders together, and effectually prevent any 

 tendency to side-canting, at the same time imparting an effective 

 appearance to the bridge. 



