34 QUESTIONS AND PROBLEMS. CHAPTER II. 



18. Does a " factor of safety of 5 " mean that it would re- 

 quire five times the calculated stress to cause failure? 



19. What factor of safety would you use in designing the 

 girders for a traveling crane? 



20. In what ways may steel be hardened? Is it possible to 

 harden steel without increasing its ultimate strength? 



21. How great must be the intensity of stress in a steel bar 

 to impair its elasticity? How great to raise the elastic limit? 



22. In what case do ordinary periods of rest not restore 

 impaired elasticity? How may elasticity be quickly restored 

 without lowering the yield point? 



23. Is the metal near a punched hole hardened more on one 

 side of the plate than on the other? See Johnson's Materials of 

 Construction, Chap. XXM. 



24. What is annealing and what effect does it have? 



25. What effect would a very large number of repetitions 

 of stress, above the elastic limit and below the yield point, have 

 upon the ultimate strength? What upon the elastic limit? How 

 does this correspond with the effect of a single stress? 



26. What does the "Launhardt Formula " take account of? 



27. What would be a good working stress for dead load 

 stress alone? For equal equivalent static alternating stresses? 



28. What working stresses would you use in designing a 

 railway bridge? 





