The New York Rapid-transit Subway

Proceedings.] PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. 41 were made on concrete in larger masses, and on the effect and value of reinforcement. As the greater part of the subway structure consisted of steel beams with intervening arches of concrete, it was deemed of special interest to ascertain the effect of these arches on the strength of the beams, though in the computations all the load was supposed to be carried eventually by the beams, and their section was proportioned correspondingly. Four 7-inch deck-beams 7 feet long were spaced 2 feet apart and embedded in concrete 8 inches deep. Two blocks of oak were set at the middle transverse to the central pair of beams, on which rested a double grillage of 15-inch beams carrying a load of pig-iron. Thus the central beams carried the whole load, the small amount transmitted vertically to the outer beams being negligible. Three sets of beams were prepared for tests. In one set the concrete was in the proportion of 1 cement, 2 sand, and 4 gravel, and in another 1 cement, 3 sand, and 5 gravel, and to get a fair average three sets of each kind were made and tested. The third set of beams was without concrete, the central pair being stiffened laterally by blocks. The steel was tested and found to have an ultimate strength of 62,000 lbs. per square inch. When loaded to destruction the average of the results was as follows, reducing the stress to that per square inch in the beams : Beams without concrete . „ with concrete 1.3.5 . » » » 1-2.4. Maximum Load. Lbs. 44,000 73,000 77,000 Stress per Square Inch. Lbs. 50,500 83,800 88,400 The plain beams failed at about the stress under which they would be expected to buckle, namely, about midway between the ultimate resistance as determined by small test-pieces and the elastic limit of the metal ; while the concreted beams carried a load equivalent to more than double the elastic limit and one-third more than the ultimate resistance : clearly indicating that even in such a form of construction the embedded beams and the surrounding concrete act together as a composite girder. At the time the tests were made the concrete was 1 month old. In the designing of the reinforced concrete the question arose whether or not it would be better to protect the rods by painting them. The general practice is not to paint, but there were no available data as to what the effect of paint was on the adhesion between concrete and the embedded steel members. Concrete blocks 8 inches square and 12 inches long were made,