ALLOWABLE STRESSES IN STEEL AND IRON. 4W, 



Formulas for Tensile Strength. Campbell gives the following formulas for the strength of 



.li i.| .111.1 IMM. nprll 111 .irth Steels: 



, i.l >t . I, Ultimate strength = 40,000 + 1000 C + 1000 P + X.Mn -f R. 



1 ,>r l.a.Mt- steel, Ultimate strength = 41,500 + 770 C + 1000 P + X.Mn + R. 



In these formulas, C = o.oi per cent carbon, P = o.oi phosphorus, Mn = o.oi per cent 

 manganese above 0.4 per .cent for acid and above 0.3 per cent for basic steel, and R is a variable 

 <lr|H'iuling upon the heat treatment of the steel. The coefficient of Mn, X, varies as follows: 

 For arid steel, for o.io per cent carbon, X = 80, and for 0.60 per cent carbon, X 480 and pro- 

 portiimal for intermediate values; while for basic steel, for 0.05 per cent carbon, X = no, and for 

 0.40 per cent carbon, X = 250 and proportional for intermediate values. 



Special Steels. The following special steels have been used. Nickel is used as an alloy for 

 structural and other kinds of steel, the specifications for structural nickel steel of the American 

 Society for Testing Materials require that there be not less than 3$ per cent of nickel. Chrome 

 steel carbon steel with about 0.5 per cent chromium was used in the Eads bridge in 1871. Chro- 

 mium is now used in combination with nickel, making Chromium-nickel steel; with vanadium, 

 making Chromium-vanadium steel, and with both nickel and vanadium, making Chromium- 

 nickel-vanadium steel. Copper steels are those having from I to 4 per cent of copper, carbon being 

 less than I per cent. Manganese steel with from 6 to 12 per cent manganese is very tough and 

 malleable. 



Specifications for Structural Steel. The allowable stresses for structural steel are given in 

 Table I and in the specifications of the American Society for Testing Materials which follow. 



Allowable Stresses in Steel and Iron. The allowable stresses Tor steel frame mill buildings are 

 given in the "Specifications for Steel Frame Buildings," in Chapter I. The allowable stresses 

 for steel office buildings are given in the "Specifications for Steel Office Buildings," in Chapter II. 

 The allowable stresses for steel highway bridges are given in the "Specifications for Steel Highway 

 Bridges," in Chapter III. The allowable stresses for steel railway bridges are given in the "Speci- 

 fications for Steel Railway Bridges," in Chapter IV. The allowable stresses in steel bins are 

 given in Chapter VIII, p. 313. The allowable stresses for steel grain bins are given in Chapter 

 IX, p. 326. The allowable stresses in steel head frames and coal tipples are given in the "Speci- 

 fications for Steel Head Frames and Coal Tipples, Washers and Breakers," in Chapter X. The 

 allowable stresses in steel stand-pipes and elevated tanks are given in the "Specifications for 

 Elevated Steel Tanks on Towers and for Stand-Pipes," in Chapter XI. The allowable stresses 

 for the steel and cast iron details in timber bridges are the same as for steel railway bridges given 

 in Chapter IV. The allowable stresses in steel reinforcement are given on page 521. 



Nickel Steel. In a paper entitled "Nickel Steel for Bridges" by Mr. J. A. L. Waddell, in 

 Trans. Am. Soc. C. E., Vol. 63, June 1909, the allowable unit stress in Ib. per sq. in. for carbon 

 steel is given as P = 18,000 70 l/r, and for nickel steel as P = 30,000 120 l/r, where / is the 

 length and r is the corresponding radius of gyration, both in inches. The impact coefficient 

 adopted by Mr. Waddell is given on page 161. 



