24 REINFORCED CONCRETE CONSTRUCTION 



factory high elastic limit steel cannot be obtained in this way. 

 To prevent brittleness a careful inspection of high steel should 

 be made during manufacture. The expense of doing this may so 

 increase the cost of the material that little or no economy will 

 result from the use of high steel, even though it be considered 

 permissible to employ a greater working stress than in the case 

 of medium steel. Open hearth steel is preferable to Bessemer 

 steel, as it is more uniform in quality and does not possess the 

 brittleness sometimes met with in Bessemer steel. 



An important test in the specifications for reinforcing steel 

 is the bending test, and no steel which fails to pass this test 

 should be used under any circumstances. In case a lot of steel 

 has been delivered without previous test by the purchaser, one 

 bar selected at random in every 100 should be subjected to this 

 test and, if it fails to pass, the portion from which it is taken 

 should be rejected. 



19. Tensile Strength. The elastic limit and ultimate strength 

 of the two general grades of steel above mentioned will range 

 about as follows: 



Medium High 



Elastic limit, Ib. per sq. in 35 to 40,000 50 to 60,000 



Ultimate strength, Ib. per sq. in. 60 to 70,000 80 to 100,000 



20. Coefficient of Expansion. The coefficient of expansion of 

 steel may be taken at 0.0000065 per degree Fahr. 



21. Modulus of Elasticity. The modulus of elasticity of all 

 grades of steel is very nearly the same and is usually taken at 

 30,000,000. (Art. 25.) If steel could be made with a high modulus 

 of elasticity, it would be especially fitted for reinforced concrete 

 work, because the higher the modulus the less the deformation 

 under any given loading. Unfortunately, however, the modulus 

 of elasticity is a constant for all the different kinds of steel. 



22. Bending Test for Steel. Medium Steel: Full-sized mate- 

 rial 1 in. thick, and over, should bend cold 180 degrees around a 

 pin, the diameter of which is equal to twice the thickness of the 

 bar, without fracture on the outside of bend. High Elastic 

 Limit Steel: Specimens for bending should bend cold under 

 the following conditions without fracture on the outside of the 

 bent portion: 



Around twice their own diameter Around their own diameter 

 1 in. diameter, 80 degrees. | in. diameter, 130 degrees, 



f in. diameter, 90 degrees. ^ in. diameter, 140 degrees. 

 \ in. diameter, 110 degrees. in. diameter or less, 180 degrees. 



