In constructing the new shop building at Swarthmore College, Swarthmore, Pennsylvania, in 1906, concrete blocks were used for the side walls, and the floors were constructed of reinforced concrete. This building is 49 feet 8

Fig. 202. Stairway in Shop Building, Swarthmore College, Swarthmore, Pa.

Fig. 202. Stairway in Shop Building, Swarthmore College, Swarthmore, Pa.

inches by 112 feet, and is 3 stories high. The floors were designed to carry a live load of 150 pounds per square foot. A factor of safety of 4 was used in all the reinforced-concrete construction.

The columns are located as shown in Fig. 200. The span of the girders is 20 feet, except for the three middle bays, in which the span is only 10 feet. The 20-foot girders are 14 inches wide, and the depth below the slab is 23 inches. The reinforcement consists of 8 bars | inch square. The details of these girders are given in Fig. 201. The beams are spaced 5 feet center to center. The span of these beams is about 16 feet, the width 8 inches, and the depth 12 inches below the slab; and the reinforcement consists of 5 bars 5/8 inch square. The slab is 4 inches thick, including the top coat of 1 inch, which was composed of 1 part Portland cement and 1 part sand. This finishing coat was put on before the other concrete had set, and was figured as part of the structural slab. The slab reinforcement consisted of

1/4-inch bars spaced 4 inches on centers, and 1/4-inch bars spaced 24 inches at right angles to the bars spaced 4 inches. The columns ranged in size from 10 by 10-inch to 18 by 18-inch, and were reinforced by placing a bar in each corner of the column, which bars are tied together by 1/4-inch bars spaced 12 inches. The amount of this steel was about one per cent of the total area of the column.

Fig. 202 shows the plans of the stairway. The lintels were moulded on the ground, and placed when the side walls had been built to the proper height for the lintels to be placed. The size of the lintels was varied on the different floors to conform with the architectural features of the building. The width of the lintels was made the same as the thickness of the walls, and therefore both sides of the lintels were exposed to view. The lintels were reinforced with 3 bars 1/2 inch square.

The concrete was composed of 1 part Portland cement, 3 parts sand, and 5 parts stone. The stone was graded in size from \ inch o 1 inch. "Johnson" corrugated bars were used as the reinforcing steel. A panel, 16 by 20 feet, of one of the 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 under side of a floor, showing the connection of the girder and beams with the column.

Fig. 203. Floor Construction in Shop Building of Swarthmore (Pa.) College, Showing Connection of Girder Beams with Column.

Fig. 203. Floor Construction in Shop Building of Swarthmore (Pa.) College, Showing Connection of Girder Beams with 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 floor line and be extended through the column. This would have tied the girders together in a more secure manner; and these bars, being near the top of the slab, would have resisted any negative bending moment.