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A concrete form, 16 by 20 feet, of one of the concrete floors, was tested by placing a load of 300 pounds per square foot over this area. The deflection was so slight that it could not be conveniently measured. In Fig. 203 is given a view of the underside of a concrete floor, showing the connection of the girder and beams with the concrete column. There is a criticism that may be made in the details of the girder shown in Fig. 201. The bars, which are turned up at the end, should have been long enough so that the bars could be again bent parallel to the concrete floor line and be extended through the concrete column. This would have tied the girders together in a more secure manner; and these bars, being near the top of the concrete slab, would have resisted any negative bending moment. In designing a reinforced concrete apartment house which was constructed at Juniper and Spruce Streets, Philadelphia, it was desirable to have a concrete floor system that was flat on the underside, except for the beams connecting the concrete columns, so as to avoid the expense of a suspended ceiling.

The greatest span of the flat construction necessary to avoid having beams in the -ceiling of the rooms, was about 18 feet. It was at first intended to use a concrete slab of reinforced concrete to connect the beams; but, as the Philadelphia Building Code requires that the depth of reinforced concrete must be at least three- fifths of an inch per foot of span, to fulfill this condition a concrete slab much thicker than necessary for structural purposes was required. The Building Code requires that the concrete floors of apartment houses shall be designed to carry safely 70 pounds per square foot. This apartment house is 40 feet by 127 feet, and eight stories in height. There is also a basement under the entire building. In taking bids on this building, it was found that a steel frame, not including the fireproofing, cost more than a reinforced-concrete concrete structure. It was therefore decided to construct the building of reinforced concrete. The concrete walls were of brick, except the eighth story, which was concrete. The concrete wall is hollow; having a total thickness of 16 inches; and it is composed of two concrete slabs, each six inches in thickness, with an air space of four inches between the concrete slabs. These concrete slabs are reinforced with steel bars placed longitudinally and vertically. The type of concrete floor construction used is shown in Fig. 204. Reinforced-concrete girders were constructed, connecting the concrete columns; and the space between them was filled with small reinforced-concrete beams and plaster blocks.

The girders were designed, when possible, as T-beams; and as a certain amount of concrete was required in the concrete slab to take compression, the hollow block construction was omitted for a sufficient width on each side of the girder to allow for this compression. The beams were 4 inches wide, 6 inches to 8 inches deep, depending on the span, and were connected with a 2-inch concrete slab of concrete. The beams were spaced 16 inches center to center, and each beam was reinforced with a 1-inch round bar. The two-inch concrete slab was reinforced with 1-inch bars spaced 24 inches; and over the girders and at right angles to the girders, *-inch bars 6 feet long were spaced 16 inches; that is, one of these bars was placed in the top of each of the beams. The span of these beams varied from 12 feet to 18 feet. A hollow plaster block, 12 inches wide, was used as filler between the concrete beams. These blocks were made of the required depth, 6 and 8 inches, and were 12 inches wide at the top and 11 inches wide at the bottom. The object was sloped on the sides of the blocks and was to key the blocks between the beams. The block, in section, is shown in Fig. 205, and is known as the Keystone Fireproof Block. The coefficient of expansion of plaster blocks is very small compared with that of the terra-cotta block; and also the plaster block is more efficient as a non-conductor of heat. The blocks were spaced 4 inches apart, and therefore served as the concrete forms for the sides of the beams. The planks on which the blocks were placed were spaced 8 inches apart, which made a saving in the amount of lumber required for concrete forms. It was found necessary to wet the blocks thoroughly by means of a hose, before the concrete was placed, as the dry blocks quickly absorbed the water from the concrete. About one per cent of the blocks were broken in handling them. The partitions in the building were made with the blocks. When the concrete floor concrete forms were removed, the ceilings and concrete walls were plastered. On the Juniper Street side, balconies were constructed nearly the full length of the house.

Are You in Marion Massachusetts? Do You Need Concrete Cutting?

We Are Your Local Concrete Cutter

Call 781-519-2456

We Service Marion MA and all surrounding Cities & Towns