The floor girders were 12 by 24-inch below the slab. The span of the girders varied from about 18 feet to about 20 feet; and they were all reinforced with 6 bars 1 inch square, three of the bars being turned up at the ends. Two i-inch square bars were placed in the top of the girders over the supports. These bars were 5 feet long, and they were hooked at the ends. Bars inch square, 5 feet long, were placed in the slab near the top, at right angles to the girders. The bars were 12 inches center to center, and were placed over the center of the girders.
The wall beams or lintels on the Fifth Street and Apple tree Street sides of the building, are shown in section in Fig. 191. They are 9 inches by 24 inches, and are reinforced with 2 bars 1 inch square. The wall girders in the side of the building opposite Appletrec Street are 14 inches by 24 inches, and are reinforced with 6 bars 1 inch square.
The stairs were constructed as shown in Fig. 192. The struc tural concrete slab was 6 inches thick, and was reinforced with inch bars. Safety treads 51 inches in width, and 12 inches shorter than the width of the stairs, were set in each step.
The concrete for the beams, girders, slabs, and footings was a Th 5 mixture; and for the columns, a 1: 2: 4 mixture was required. The stone used in this concrete was trap rock. The concrete was mixed in a batch mixer, and the consistency of the mixture was what is commonly known as a wet mixtlere. Square twisted bars were used as the reinforcing steel.
The first, second, and third floors were finished with 11-inch maple flooring. The stringers, 2 inches by 3 inches, were spaced 16 inches apart, and the space between the stringers was filled with cinder concrete. The other floors were finished with a one-inch coat of cement finish. A cinder fill 2 inches thick was laid on the concrete floor-slab, on which was laid the cement finish. The cinder concrete consisted of 1 part Portland cement, 3 parts sand, and 7 parts cinders. The cement finish was composed of 1 part Portland cement, 1 part sand, and 1 part +-inch crushed granite.
3S2. Mershon Building. Fig. 193 shows the plan of the foundations and the typical layout of the structural members for each floor of a building constructed by Cramp Company on the south side of Walnut Street, between Ninth and Tenth Streets, Philadelphia.
This building was erected during the sum mer of 1907. It has a frontage of 27 feet on Walnut Street, and a depth of 165 feet on Hutchinson Street, and is eight stories high. It was constructed for manufacturing and storage purposes, and the floors were designed to carry a uniformly distributed live load of 200 pounds per square foot.
At the time that this building was constructed, the Building Code of Phila delphia permitted a working stress of 500 pounds per square inch in compres sion in concrete, and a tensile strength of 16,000 pounds per square inch in the reinforcing steel. The concrete could be made of any desired proportions that would insure an ultimate strength of 2,000 pounds per square inch. A thick ness of 2 inches of concrete was required on the outside of the reinforcing steel in col umns, girders, and beams, and 1 inch on the bottom of floor slabs. The Building Code re quired that all girders, beams, and slabs should be considered as simple beams supported t, t the ends, no allowance being made for continuous construc tion over supports. Owing to the building being only 27 feet wide, interior columns were not required, and there fore footings were needed only along the two sides of the building. The footings along the Hutchinson Street side of the building were designed as isolated footings, as shown in the genera] plans, and detailed in Fig. 194. But this type of construction could not be used to support the columns of the opposite side of the building, owing to the adjacent prop erty; and therefore a continu ous footing was used. This footing, which is 3 feet deep, 6 feet wide, and reinforced with 1S twisted bars 1 inches square, is really an inverted beam with a span of 14 feet Di inches. In designing this inverted beam, the load was considered the same as the load permitted on the soil, which was 3', tons per square foot. See Fig. 105.