STATE GEOLOGIST. 125 
Geometrical and algebraic determinations of the moment of resistance 
of armed pieces, influence of the quality of the concrete and of the arma- 
tures, the most economical percentage of metal, effect of bad workman- 
ship, value of the factor of safety, and the utility of symmetrical arma- 
tures.” In more recent years Edwin Vhacher has published from time to 
time the results of a careful mathematical investigation of the theory. 
RECENT USE OF REINFORCED CONCRETE. 
During the last four or five years many different systems have been 
developed, few of which have introduced any radical ideas into reinforced 
concrete construction. 
Concrete has great compressive strength, but lacks reliable, uniform 
tensile strength. Engineers have sought to take advantage of the strength 
of concrete in compression for all classes of construction, but to do so 
they must insert some material to supply the much needed tensile strength, 
hence they have imbedded steel and iron bars of various sizes and shapes, 
in the various positions in the concrete mass where they conceive the 
tensile strains will occur. Tests have proved conclusively that greatly 
added strength has been given to such structures. 
Professor W. K. Hatt,* Purdue University, Lafayette, Ind., has car- 
ried on a series of tests with his senior students which very clearly show 
the effect of reinforcing concrete beams. Concrete beams 8 by 8 inches 
square were tested in lengths of 80 inches between supports. The several 
beams were reinforced by 54 and 34 inch iron bars placed 1 and 2 inches 
from the lower face of the beam. The majority of the tests were made 
upon concrete composed of I part cement, 2 parts sand and 4 parts broken 
stone. A few tests were made upon cinder concrete and some with gravel 
concrete. The variables tested were age, per cent. of steel, position of 
steel and material. 
One per cent. of reinforcement placed 1 inch from the bottom in- 
creased the strength of the plain concrete beams from 2,200 to 7,400 
pounds, and increased the flexibility of the beam from a center deflection 
of 0.01 inch to 0.14 inch. 
Two per cent. of reinforcement increased the strength from 7,200 to 
10,000 pounds with only a slight increase in the flexibility. Raising the 
I per cent. of metal 2 inches from the bottom face decreased the strength 
from 7,200 to 5,000 pounds, with a slight decrease in flexibility. 
“A cinder concrete and a stone concrete beam each reinforced with 
2 per cent. of metal, 1 inch from the bottom face, had comparative strengths 
of 5,000 and 10,000 pounds, respectively, and a comparative flexibility of 
0.26 and 0.16 inch, respectively. In case of plain cinders and stone 
concrete beams, the comparative strength was 600 and 1,800 pounds, and 
*Hng. News, July 17, 1902. 
