A high elastic limit in steel can be attained in three ways only : 



(1) By the increase of the percentage of carbon in the steel. 



(2) By the special process of repeated cold drawing and annealing encountered in the 

 manufacture of wire. 



(3) By the cold working of a soft steel, as in cold-twisting squares, or in cold rolling bars, 

 or in the making of "Steelcrete" Expanded Metal. 



We will consider the first and last cases together, and the second will be taken up subse- 

 quently. In the last case referred to the material is a soft or medium steel containing between 

 .08 per cent to .20 per cent, of carbon. This is usually designated in the trade terms as 8 to 20 

 carbon. A high carbon steel, such as is commonly used in concrete work, in order to attain the 

 high elastic limit reached, contains from .40 per cent to .50 per cent of carbon, or, in trade terms, 

 40 to 50 carbon. It is an incontrovertible fact that a high carbon steel cannot be attained in the 

 present market in a uniform quality except under conditions of inspection that do not permit 

 its use as a commercial reinforcement. On the other hand, it is indisputable that a low carbon 

 steel is easily obtained commercially in a uniform quality. When high carbon steel is bought, an 

 inferior product is bought. On account of its unreliability its lowest values can only be consid- 

 ered in the selection of the working stresses. 



"Steelcrete" Expanded Metal contains between 8 to 12 carbon, and is therefore a uniform 

 product. This Expanded Metal could not be made from non-uniform steel, as the process of 

 manufacture, to be a commercial success, absolutely requires a uniform material. 



With high carbon bars must be classified the ordinary commercial wire meshes often used 

 as a reinforcement. Wire mesh is not uniform in quality. While published tests show average 

 values of 85,000 to 95,000 Ibs. per sq. in. in ultimate strength, and elastic limits of over 60,000 

 Ibs. per sq. in., tests on commercial products show a range of from 60,000 to 120, 000 Ibs. per sq. 

 in. in ultimate value, and in elastic limit of from 40,000 to 97,000 Ibs. per sq. in. While the 

 average values' may be high, we submit that average values have no place in conservative engi- 

 neering, inasmuch as the strength of a chain is that of its weakest link, the minimum values 

 should in every case be required. Furthermore, we submit that it should be prohibitive to- use 

 a material with a variation in quality as above stated. The ranges above given are unquestion- 

 ably conservative, and the actual range is undoubtedly greater. 



Methods of 

 Attainment 



Effect of 



Carbon 



Contents 



11 



