Railway Construction

by William Hemingway Mills

suitable distances, and carry simple roof-principals of convenient spans. In some cases the roof-principals are placed as shown in [Figs. 407 and 408], and in others as in [Fig. 409].

In another system the roof-principals are incorporated with the main truss-girders, as in [Fig. 410].

With the above type of covering the truss-girders take the place of the arched wrought-iron girders and cast-iron columns, as illustrated in [Fig. 406], but will be more costly, as may be gathered from the following brief comparison: Assuming the area to be covered as 480 feet long and 180 feet wide, then the width of 180 feet could be divided into three spans of 60 feet each, or one centre span of 65 feet, and two of 57 feet 6 inches if they would work in more conveniently. With columns at 48-foot centres longitudinally, the three-span arrangement would contain the following:—Twenty cast-iron columns in the two rows, or twenty-two columns if two columns are placed side by side at the extreme end; 960 lineal feet of light arched wrought-iron girders in twenty girders of 48 feet span.

On the other hand, with the truss-girders placed at 40-foot centres to suit roof-principals resting on the tops of girders, as shown in [Fig. 409], or to suit the arrangement shown in [Fig. 407], there would be twelve heavy truss-girders, each of 180 feet span, making a total length of 2160 lineal feet of deep truss-girder work, exclusive of about another 60 lineal feet, which would be required for the bearings on the side walls.

The successful lighting by day of a large roofed-in station will depend principally upon an appropriate distribution of the glazed portions. With a large span, and the glass skylights placed near the apex, the side lines and platforms will be much less efficiently lighted than those near the centre; and again, if the glazed parts are only at the sides, then the centre portion will be rather in the shade. Where possible it is better to place the glazed portions and slated portions alternately, so as to obtain a more uniform light all over the centre area, somewhat similar to the arrangement shown in [Fig. 406].

Roofs over passenger platforms at roadside stations are made in many types, the arrangement depending in a great measure upon the width of platform to be covered. In many of the earlier stations the roof was extended across from side to side, and included the lines of rails as well as the UP and DOWN platforms, a system which was not only costly, but had the

disadvantage that the steam and smoke from passing trains remained for some time under the roof before it was thoroughly dispersed. The more modern and more economical plan is to put the roof or shelter over the platforms only, and allow the steam and smoke to pass away into the air. In designing the latter class of roof, the fewer supporting columns the better, so as to diminish as far as possible the obstructions on the platforms. Where the platform is unavoidably narrow, the roof may be carried on curved brackets projecting out from the walls.

Except in tropical countries, where shade is more acceptable than strong light, a liberal amount of glass should be provided in these platform roofs. On many of our home railways they are entirely covered with glass, and the abundance of light is found to be of great assistance in the working of the traffic. [Figs. 411] to [420] are sketches of a few out of the many types of small roofs which have been erected over single and island platforms.

Goods-sheds.—The form and dimensions of a goods-shed for any station must be determined by the description and amount of traffic to be transacted at the particular place. With an estimate of the traffic before him, the engineer must consider the internal arrangement of building most suitable for the bulk of the merchandise to be accommodated. The principal object of the shed is to permit of goods being transferred under cover from or to railway trucks or carts without being exposed to the weather, and the transfer will be expedited if the arrangements are made the most convenient for the particular class of merchandise presented.

For some commodities it is considered preferable to unload direct from the railway trucks into carts, or vice versâ, and thus have only one handling of the goods. To comply with this method, the cartway must be made almost down to the same level as the rails, to allow the carts or drays to be drawn close up alongside the railway trucks, as shown in [Figs. 427 and 428]. This type of shed implies a constant supply of carts, so as not to detain the railway trucks, or necessitate the stacking or storing of goods on the low level floor in the way of carting movements.