STRENGTH OF CONCRETE. XXIII. 



THE STRENGTH OF CONCRETE. 



By W. H. Warren, m. Inst, c.e., m. Am. Soc. c.e., Challis Professor 

 of Engineering, University of Sydney. 



[Read before the Engineering Section of the Royal Society of N. S. Wales, 

 September 18, 1901.) 



The tests described in this paper, on concrete subjected to com- 

 pression, transverse, and tensile stresses have extended over 

 several years, and it was thought desirable to publish them for the 

 benefit of those who are engaged in the construction of works in 

 which this material is used. It is hardly necessary to point out 

 that we require to know the resistances of concrete when subjected 

 to the stresses above mentioned, in designing concrete columns, 

 walls, arches, and foundations. 



Compressive strength of concrete. — It is usual to determine the 

 compressive strength of concrete by subjecting cubes of the 

 material to a compressive stress in the testing machine. The 

 strength of a cube is greater than that of a square prism, the height 

 of which is greater than the sides of the cube, and less than that 

 of a prism the height of which is less than the side of the cube. 

 In a paper on the Strength of Brickwork read before the Society 

 in December 1900, the results were given of some experiments on 

 the compressive strength of slabs and prisms of cement and lime 

 mortar in which the sectional area was the same in each test, but 

 the height varied from J an inch to 12 inches. 



Professor Bauschinger has expressed the compressive strength 

 of prisms of different heights of the same sectional area as follows: 



where cr denotes the compressive strength, /the sectional area, I 

 the height of the prism, a and /3 constants to be determined by 

 experiment. For prisms of dissimilar cross sections, he proposed 

 the following formula : — 



