THEORY AND PRACTICE OF CONCRETE-IRON CONSTRUCTIONS. 107 



concrete of a high elastic limit, and are independent 

 of whether the iron be smooth or rough. 



4. Concrete with iron insertions can undergo elongations 

 which far exceed those of ordinary plain or unarmoured 

 concrete, and generally speaking may be stated to be 

 from 10 to 20 times greater. 



Test pieces made to ascertain the elongations of plain 

 and armoured concretes, consisted of prisms of square 

 cross-section of 2*36 inches sides, and 23*6 inches length. 

 Each prism was fixed vertically, well clamped at the lower 

 end — while over the top was fitted a horizontal lever by 

 means of a square eye of the dimensions of the cross-section 

 of the prism. At the end of this lever the loads were 

 applied, and by this method of testing equal bending 

 moments were created in all cross-sections producing 

 elongations on the one side and shortenings on the other. 

 The concrete in all the prisms cousisted of 1 of cement to 

 3 of sand. 



The concrete-iron or armoured prisms contained 3 iron 

 rods of 0*167 inch diameter, which latter had an elastic 

 limit of 54,000 lbs. per square inch. The plain concrete 

 prisms showed just before fracture a shortening of '0037 

 inch per lineal foot on the compressive side and an elonga- 

 tion of *0024 to '003 inch per lineal foot on the tension side. 

 The concrete-iron prisms showed an elongation of '024 inch 

 or a ten times greater lengthening than occurred in the 

 plain concrete prisms. 



Further tests proved that a prism of concrete composed 

 of 1 part cement, 2 of sand, and 4 of broken stone, 3*9 inch 

 square, 6*56 feet long, with 4 iron rods of *023 inch diameter 

 inserted, could endure an elongation of *007 to *016 inch 

 per lineal foot without fracture, whereas the plain concrete 

 prisms did not elongate more than from '0018 to '0036 inch 

 before fracturing. 



