148 W. H. WARREN. 



The expression 



p s = E s K 



is true only when A s includes the initial strain due to 

 shrinkage as well as that due to the applied load. The 

 initial stress upon the longitudinal rods in a concrete prism 

 set in air may be very near to the intensity of stress at 

 the elastic limit of the metal, and thus the rods begin to 

 deform plastically with very moderate intensities of stress 

 and contribute very little to the strength of the prism. 

 The strength in any case cannot differ much from that due 

 to the sum of the resistances of the concrete to crushing, 

 and to the resistance of the rods up to the elastic limit of 

 the metal. 



If A = the area of cross section of prism. 

 a = the area of rods. 



c = the compressive strength of the concrete. 

 w= the total load carried. 



Then, x . E, \ 



w = c A + - E ~ a) 



In IV. m. 1, the shortening of the prism per inch with a 

 stress of 1806 lbs. per square inch was 0*000725 inch, cor- 

 responding with a stress of 21750 lbs. per square inch. If 

 we add to this stress, the initial stress due to shrinkage, 

 say 7,000 lbs. square inch, we have 28750 lbs. per square 

 inch as the total intensity of stress on the rods when the 

 prism is under a stress of 1806 lbs. per square inch. At 2409 

 lbs. per square inch, when the prism fractured, the stress 

 on the rods would be much greater, so that there is very 

 small margin remaining which is available in the case of a 

 reinforced prism. 



Concrete reinforced with transverse rods or grills. — 

 The tendency to shear along oblique planes is resisted by 

 rods whether they are arranged parallel with or at right 

 angles to the direction of pressure, in consequence of the 



