18 QUESTIONS AND PROBLEMS. CHAPTER I. 



1. What is statics? 



2. May a structure be composed of simple beams, girders, 

 and trusses? What are the constituent parts of a truss called? 



3. Which members are the web members of a truss? 



4. When is the force of the wind taken as a live load? 



5. Give three examples of a concentrated load and three 

 of a distributed load. 



G. How may impact stresses be measured? 



7. What were the main conclusions at which Prof. Turn- 

 eaure arrived, in his investigations of the vibrations of railway 

 bridges? 



8. What is the total equivalent static stress in a member 

 of a bridge truss, for which the dead-load stress is 70000 Ibs., the 

 live-load stress 200000 Ibs., and the impact stress is taken as 



300 

 7- times the live load stress, L being 150 in this case. 



olHJX Li 



Ans., 403300 Ibs. 



9. What are the principal uses to which the materials men- 

 tioned in Art. 6 are put? Which of these materials is the heav- 

 iest? Which are brittle? Which are ductile? Which has the 

 greatest strength? 



10. What, according to Johnson's Materials of Construc- 

 tion, is the elastic limit of steel? Of long-leaf pine? Of steel 

 piano wire? 



11. What is the stress per square inch in a steel tension 

 member which carries a stress of 64000 Ibs., and whose area of 

 cross section is 6.4 sq. ins.? What total stress will it carry if the 

 working stress is 12000 Ibs. per sq. in.? 



12. If the coefficient of expansion of steel is 0.0000085 and 

 of concrete 0.0000055, what kind of stress will be induced, by a 

 fall of temperature, in a bar of steel imbedded in the center of 

 a block of concrete, if the adhesion is perfect? What kind in 

 the concrete? 



13. If E = 29000000, what will be the total elongation of a 

 steel bar 20 ft. long, having a section 6 in. X 1J in., and carrying 

 a stress of 108000 Ibs. in tension? 



ir losooo 



= s = ^ - . = 12000 Ibs. per sq. in. 



/I U X I 2 



dL = 0.000413X12X20 = 0.099 in. 



