The New York Rapid-transit Subway

22 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of the lower half of the structure was put in (Fig. 11, Plate 5). In both cases the side sheeting was not drawn, but was left in place. The Elevated Sections. The elevated portions of the railway are for the most part a three- track structure, and consist of two rows of columns connected at the top by cross plate-girders carrying the longitudinal track-girders. Generally the elevated portions are built along streets with wide road- ways; so wide, in fact, that to have placed the columns on the foot- walks would have involved such deep and heavy cross girders as to be both expensive and awkward. Except in some special localities, the columns were therefore placed in the roadway 29 feet apart between centres, affording space for a double-track tramway along the street and beneath the structure, and a space for other vehicles between the columns and curbs. Longitudinally their location was governed by cross streets and other local conditions, but usually they were set about 50 feet apart. The general features of this design are shown in Figs. 12 and 13, Plate 6, and call for no special notice other than a few words as to the cross section of the columns, the connection between the columns and the cross girders, and the expansion-joints of the longitudinal girders. The columns are similar in design to, but of larger detail than, the small subway columns (Fig. 3, Plate 5), consisting of four bulb- angles with a single connecting plate. This design of column rendered possible a special connection between the top of the column and the cross girders. The usual plan is either to rest the cross girder on the top of the column and use a stiffening bracket in the corner between the two, or to rivet the end angles of the cross girder directly to the side of the column, throwing the vertical load in shear on the rivets. The single plate between the four angles was omitted for several feet at the top, and the outer pair of angles was extended beyond the normal length of the column by the depth of the web of the cross girders. The angles of the bottom chord of the cross girder were cut off by a length equal to the width of the column. The web of the cross girder was in three sections, the central section being the required depth of the girder, but the two end sections being deeper than the girder at the ends by several (usually 5 or 6) feet. In erection, after the column had been set up, the projecting webs of the cross girders were slipped in between the vertical angles of the column, which were then all riveted together. It will thus be seen that the same plate acted as the column-web and girder-web, and that the vertical angles of the