STRENGTH AND ELASTICITY OF REINFORCED CONCRETE. 151 



In this case the rods appear to have contributed nearly 

 their full amount, assuming the spirals contributed the 

 same amount as in No. 2 tests. 



Concrete prisms 24 inches long, Fig. IV. k. 

 No. 1. Compressive strength of concrete prism, not rein- 

 forced = 2786 lbs. per square inch. 

 No. 2. Reinforced with spiral 5 inch diameter of wire 0*2 



inch diameter = 4098 lbs. per square inch. 

 Increase clue to spiral = 1312 flbs. per square inch. 

 Ratio of area of metal to concrete == *022 



•022 x 39000 = 858 lbs. per square inch. 



■o .. 1312 1-RQ 

 Ratio — — - =■ 1 53 



808 



No. 4. Total strength of prism = 5270 lbs. per square inch. 

 Increase due to spiral and concrete from No. 2 test = 4098 



lbs. per square inch. 

 Difference due to 6 rods of Bessemer steel \ inch in 



diameter = 1172 lbs. per square inch. 

 Area of rods = 6 x 0*196 == 1*176 square inch. 



Resistance = 1 ' 176 x 3777 _ 1490 ft square inch. 



29*5 1 



Hence the rods contributed about 80f° of their resistance. 



No. 5. Total strength of prism = 4214 lbs. per square inch. 



Resistance due to concrete and spiral from No. 2 test = 



4098 lbs. per square inch. 



Difference due to rods = 116 lbs. per square inch. 



The 10 rods | inch diameter should have contributed 1400 

 lbs. per square inch, so that the longitudinal rods in this 

 case did not contribute their proper proportion, due prob- 

 ably to initial stresses In consequence of shrinkage of 

 concrete. 



The experiments recorded in Tables IV. m. and IV. k. 

 show that prisms of concrete reinforced with spirals of soft 

 steel or iron possess considerable ductility and sustain large 



