The New York Rapid-transit Subway

IG PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of 2 feet, so as to rest on the horizontal legs of the angles just mentioned and to surround the longitudinal rods completely. Tn the wall, and connecting the vertical angles, there were two 3-inch horizontal rods bolted to the angles, the rods being set 4 inches apart, with the lower one 18 inches below the under surface of the roof. The roof concrete was again moulded to a cornice with a curve to the sides as in the centre, so that the -inch horizontal rods just described formed the tension-member of a longitudinal truss on the top of the walls. In order to ensure distribution of reaction at the tops of the central columns, or, what is the same thing, to false up the reverse stress over the tops of the columns, IJ-inch rods 6 feet long were placed laterally 8. inches between centres, with centres 23 inches below the top of the finished concrete. These short rods served as a tension-member in the roof, considered to be acting as a continuous beam over the columns. The thickness of the concrete in wall and roof varied with the loading to which it was to be subjected. For cover 6 feet or less in depth the walls were made 14 inches thick; for cover 6 to 10 feet deep the walls were made 16 inches thick. The roof concrete was given the following thicknesses :— For 5 feet of cover ..............................183 inches » 6 to 7 feet of cover ..........................193 ,, » 8 to 9 » » .....................................204 „ „ 10 feet of cover .............................211 In designing, 500 lbs. per square incli was allowed in compression on the concrete and 12,000 lbs. per square incli in tension on the steel. Wherever the base of the rail was beneath water and there was upward hydrostatic pressure, the floor concrete was given a minimum thickness of 15 inches to the upper surface of the water- proofing, instead of 8 inches under normal conditions. The upper surface of the floor concrete was then reinforced with 14-inch rods, 12 inches apart, with the centres 3 inches below the top surface of the concrete. Two 11-inch rods were set longitudinally beneath the central row of columns and other l{-inch rods, 6 feet long, were placed laterally beneath the central columns, to distribute the stress set up during erection. The first trial was found to give such excellent results that the same principle, with details varying to suit local conditions, was adopted for other sections where the work had not been begun. The advantages of reinforced concrete construction are: economy in cost; rapidity of erection; use of non-skilled labour; employ-