STRENGTH AND ELASTICITY OF REINFORCED CONCRETE. 143 



of at least 1361 lbs. per square inch, was contributed by 

 the five steel bars f of an inch in diameter, or the stress 

 in the bars was 22190 lbs. per square inch. The extension 

 recorded for a load of 14000 lbs. was 0*001563 inch, so that 

 the metal must have slipped 'in the mortar, as the elastic 

 extension of the rods was only 0*0007396 inches. Similar 

 slipping occurred in I. b. 4 and I. b. 5, and to a smaller 

 extent in I. b. 2. In like manner, in Table II., slipping 

 occurred in II. d. 3, II. e. 1, II. e. 2, II. f. 1, II. f. 3 and in 

 some others. And in general whenever the extension 

 recorded in column 5 exceeds that of the elastic extension 

 of the steel rods for the actual stress upon the rods, the 

 difference is due to slipping, or in other words the partial 

 failure of the adhesion of the mortar or concrete to the rods. 



In fig. I. a. the resistance of the reinforcement is denoted 

 by straight lines 1 f., 2 f. and 3 f., on the assumption that 

 no slipping occurred. The diagrams 1, 2 and 3 are at first 

 curved and afterwards become straight lines. For any 

 given extension within the elastic limit of the steel, the 

 intercept between the straight line representing the steel 

 and the curve representing the reinforced specimen, is the 

 total resistance contributed by the mortar or concrete. 



A further test was made in which the length of the head 

 measured from the extremity of the parallel portion was 

 14 inches, instead of 7 as in the other tests, thus providing 

 a greater adhesion area. The concrete consisted of 1 of 

 cement, 2 of sand, 3 of f inch shivers, reinforced with 5 

 steel rods \ inches in diameter. At 99 days the total load 

 sustained was 16500 lbs., or 1030 lbs. per square inch. Taking 

 the strength of the concrete at 300 lbs. the rods contributed 

 730 lbs. per square inch, sustaining a total pull of 11680 lbs. 

 or 11918 lbs. per square inch. The extensions were, how- 

 ever, in excess of that due to the steel for the stress 

 developed, and at fracture the extension was 0*001855 inch 



