324 LIMITING STRESSES. 



Wohler's Limiting Stresses on Wrought Iron and Steel. 



In this table the plus sign means tension and the minus 

 sign compression. These results show that only in the 

 case of a structure or parts of a structure under a dead 

 load does the safe stress depend on the ultimate strength 

 of the material divided by a standard " factor of safety," 

 and that, where the structure is subjected to repeated and 

 variable loads, the safe stress allowed must be chosen 

 with due consideration of the number of repetitions of 

 the stresses as well as of the complete range of stress 

 imposed. 



Besides those of Wohler, other experiments have been 

 made in the same direction, notably by Bauschinger and 

 Sir B. Baker. For use in designing parts of structures 

 subjected to repeated stresses, several formulas have been 

 devised embodying the results of these endurance tests. 

 Especially to be noted are those of Launhardt and 

 Weyrauch. 



