STRENGTH AND ELASTICITY OF REINFORCED CONCRETE. 147 



The mean strength of the reinforced prisms IV. g. 1 and 

 2, 182 days old was 1803 lbs. per square inch, and of similar 

 prisms unreinforced, but 21 days older, 1555 lbs. per square 

 inch; IV. d. 3 and IV. e. 1 giving a difference of 248 lbs. 

 per square inch only, which is only about half as much as 

 the actual resistance of the reinforcement. 



The mean resistance of the reinforced prisms IV. g. 3 

 and 4, 173 days old, similar to IV. g. 1 and 2, but with 10 

 and 15 cross ties respectively, was 1985 lbs. per square inch, 

 which compared with similar unreinforced prisms 30 days 

 older shows a difference of 430 lbs. per square inch, due to 

 the reinforcement, but although this would account for the 

 resistance contributed by the rods, it is below what might 

 have been expected from the rods and cross ties combined. 



The prisms IV. h. 1 and 2 are reinforced with 7 grills, 

 each consisting of 8 bars yV inch in diameter arranged 

 transversely. These prisms gave a mean strength of 2398 

 lbs. per square inch at 106 days, or an excess of 391 lbs. per 

 square inch over similar prisms not reinforced but 192 days 

 old, so that the value of this kind of reinforcement appears 

 to be not as good as the longitudinal rods and cross ties of 

 the same volume. 



Concrete reinforced by longitudinal rods. — Tables IV. m. 

 and IV. k. and Figs. IV. m. and IV. k. give the results of 

 testing concrete prisms octagonal in cross section, having 

 an area of 29*75 square inches. The lengths of these prisms 

 were 24 and 12 inches respectively. The object of these 

 tests was to ascertain the effect of reinforcing with soft 

 wire spirals with and without longitudinal rods of steel. 



M. Considere has pointed out that when concrete prisms 

 reinforced witli longitudinal rods are allowed to set in water 

 the rods are extended, due to the swelling of the concrete, 

 and when allowed to set in air they are compressed. 



