The New York Rapid-transit Subway

34 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of or the side-wall column is 1 foot 3 inches. Wherever a curve would bring the sides or end of a car nearer to a wall or column than that distance the track-span was widened correspondingly. Methods of Dealing with Sub-surface Structures. The greatest difficulty to be overcome in building a shallow subway is the disposal of the sub-surface structures. In this respect New York does not differ materially from London or any other large city, except that there are found, in addition to other structures occurring elsewhere, elevated-railway piers and a very complex surface tram- way-system. House-vaults were held not to be property, but only a revocable license from the city. The owners therefore received as compensa- tion only the price paid originally to the city for the right of use. A few instances dated back to colonial and early times, when the original price was stated in bushels of wheat. The city repaid not in kind but in the marlset value of the grain on the date of settlement. The elevated structures where encountered were carried by temporary supports, and the foundations were then removed. In making a permanent connection between the column and the roof of the subway two different methods were used, either reinforced con- crete or the standard beam construction. In reinforced concrete there were built in the side walls two 12-inch 40-Ib. beams, spaced 5 feet between centres and symmetrical with the centre-line of the column to be carried. Resting on these girders and carried to the first row of bulb-angle columns were two 24-inch 90-lb. I beams with four 12-inch 314-lb. I beams set between them, resting on the lower flanges and covering a total span about 5 feet square, q-inch rods for construction purposes passing through the webs of the main I beams to hold them together (Fig. 19, Plate 6). The large and small I beams were then encased in concrete, an ordinary layer of waterproofing being placed on top, carrying a concrete pyramid 6 feet or 7 feet square at the bottom, to distribute the load of the elevated column above. The small I beams were probably not necessary, being introduced in Brooklyn at the request of the officers of the Elevated Company. The mass of concrete suffices to distribute the load over the main I beams without bringing any stress on the small beams. In beam construction the supporting structure was built in the ordinary manner, except that the roof-beams that came beneath the elevated columns were made of heavier section.