The New York Rapid-transit Subway

Proceedings.] PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. 43 the enlargements and the twists. If a mechanical bond is desired in addition to adhesion it can be better obtained by a square shoulder, such as a nut on the end of the rod, than by any shape that tends to split the enveloping mass. A series of tests was made on reinforced-concrete beams using various methods of reinforcement. The beams were 8 inches by 8 inches in section and 5 feet long, but so set up for testing as to have an effective length of 4 feet 10 inches between bearings. The concrete was made with fine gravel in the proportions 1 of cement, 2 of sand, and 4 of gravel, and when tested in 6-inch cubes had an ultimate resistance to crushing of about 1,800 lbs. per square inch at the end of 1 month, and 2,300 lbs. at the end of 3 months. The steel used in reinforcement had various qualities, as shown in Table VII. Table VII. Kind of Rod. Ultimate Strength per Square Inch. Elastic Limit per Square Inch. Lbs. Lbs. Plain rods, square 62,000 42,600 Expanded rods, soft 58,000 34,000 ,, » medium 66,500 40,000 „,, hard 70,000 45,000 Twisted ,, 80,700 55,000 Corrugated 93,700 62,000 Hennebique „ square 66,100 45,000 The load was applied at the centre of the beams by a powerful slow-moving testing-machine, the load being released at the time of the first crack in order to measure the permanent set and the total central deflection, and then reapplied until the beam finally yielded. For computing the distribution of load between the concrete and the steel reinforcement the usual formulas, based on the respective moduli of elasticity were used, the modulus for concrete being assumed at 1,500,000 lbs. and that for steel at 30,000,000 lbs. per square inch. Table VIII records the tests, the general results, and the reduction of the load to stresses per square inch on both concrete and steel. Inspection of this Table shows good uniformity in result, especially as regards the ultimate load. The irregularity in the load producing the first crack is to be expected, for in many instances such a crack