. Railroad structures and estimates . - shelter roofs built of reinforced-concreteunits. The roofs are of the butterfly or concave type,sloping down from the eaves to a central gutter. There arefour platforms 740 ft. long and 16 ft. wide, with roofs 18 The main construction consists of a central row of T-headcolumns, spaced 20 ft. center to center and carrying two rowsof roof slabs 20 ft. long. (Fig. 161a.) The columns are 12X 24 at the base and 12 X 18 at the top, with caps or heads10 ft. long and 17 in. deep. On each side of the cap is a recess,forming a shelf for the end of the roo
. Railroad structures and estimates . - shelter roofs built of reinforced-concreteunits. The roofs are of the butterfly or concave type,sloping down from the eaves to a central gutter. There arefour platforms 740 ft. long and 16 ft. wide, with roofs 18 The main construction consists of a central row of T-headcolumns, spaced 20 ft. center to center and carrying two rowsof roof slabs 20 ft. long. (Fig. 161a.) The columns are 12X 24 at the base and 12 X 18 at the top, with caps or heads10 ft. long and 17 in. deep. On each side of the cap is a recess,forming a shelf for the end of the roof Fig. 161a. Placing Roof Slabs. Reinforcing bars projecting from the ends of the slabs lapeach other over the top of the cap and are embedded in cementmortar, which is filled in over the cap to the level of the longitudinal joint between the slabs is also filled with cementmortar. A roofing composition is laid upon the completedshelter. At intervals of about 340 ft. an expansion joint isprovided, covered with copper flashing. The roof slab has a minimum thickness of 4 in. (increased togive an incline for drainage) and is stiffened by six transverseribs. The columns are set in sockets, 18 in. deep, in pedestalfootings. PLATFORM SHELTERS. 337 A variation in this construction is required where the inchnedramps connect the platforms with the subway beneath thetracks. Here the roof is carried by two-column bents, asshown in Fig. 161b. These columns are 8 X 12, connectedby an arched cap. They, are set in steel sockets in the steelframing of the subway roof. Engineering News, July 1
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