STRENGTH AND ELASTICITY OF REINFORCED CONCRETE. 149 



equality of the intensities of shearing stresses on planes at 

 right angles to each other, so that transverse rods behave 

 in a manner very similar to longitudinal rods. 



Concrete prisms reinforced by means of spirals of soft 

 iron or steel wire. — M. Oonsidere has shown that a prism 

 of sand reinforced by a continuous shell offers 2*4 times the 

 resistance of the sand when reinforced by longitudinal rods 

 of the same weight as the shell, and he infers that spirals 

 or hoops are 2*4 times as effective as the same weight of 

 metal arranged as longitudinal rods in a concrete prism. 

 The spirals are in tension from the swelling of the concrete 

 which is much smaller than the longitudinal shortening of 

 the rods, and concrete reinforced by spirals can sustain 

 great deformations without injury to either metal or con- 

 crete. The compressive resistance of a concrete prism 

 reinforced with spirals and longitudinal rods is the sum of 

 the resistances due to : — 



1. The compressive resistance of the plain concrete 



without reinforcement. 



2. The compressive resistance of the longitudinal rods up 



to their elastic limit. 



3. The compressive resistance which would have been 



produced by imaginary longitudinal rods at the elastic 

 limit of the material used in the spirals, the volume 

 of the imaginary rods being 2*4 times that of the 

 spiral. 



Remarks — On the compressive strength of reinforced 

 concrete prisms, octagonal in cross section : — 

 Area 29*75 square inches, Fig. IV. m., length = 12 inches. 

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

 forced = 2409 lbs. per square inch. 

 No. 2. Reinforced with a spiral 5 inch in diameter of wire 



0*2 inch in diameter =*? 4220 lbs. per square inch. 

 Increase due to spiral = 1811 lbs. per square inch. 



