QUESTIONS AND PROBLEMS. CHAPTER VI. 123 



1. What constitutes the web and what the flanges of a 

 plate girder? Are there corresponding parts in a truss? 



2. Illustrate five cases of beams supported in different 

 ways. May one span of a continuous beam be considered as 

 fixed at its ends? 



3. Why are stresses in beams investigated on sections per- 

 pendicular to their axis? What kinds of stresses are found on 

 these sections, in general? 



4. Are the three equations of equilibrium applicable in 

 beams having only vertical loads? 



5. What, according to the theory of flexure, is the relation 

 between the unit elongations of fibers in a beam at distances 

 of 2 inches and 12 inches from the neutral axis? What is the 

 relation between the unit stresses in these fibers? What law is 

 involved? 



6. Upon what does the variation of the total stress on a 

 cross section of a beam depend? 



7. State the facts contrary to the first assumption in the 

 theory of flexure. To the second. To the third. 



8. To what is the moment of resistance of a rectangular 

 cross section equal? Derive this from the general formula. 



9. What is the difference between the moment of inertia 

 and the statical moment of the area of a cross section? How 

 should a given area be disposed with respect to the neutral 

 axis in order that either may be as large as possible? 



10. What is the greatest stress in a timber floor joist, 

 3"xl2", if the maximum moment is 12000 ft. Ibs.? 



11. What are the unit stresses in the extreme upper and 

 lower fibers of a beam composed of two angles 6"x4"x", the 

 longer legs being vertical, and the maximum moment being 

 138800 in. Ibs.?. Ans. 7930 and 16000 Ibs. per sq. in. 



12. Upon what does the section modulus depend? 



13. What are the section moduli in problem 11? 



14. Do the section moduli given in the Cambria handbook 



equal for I beams and channels? 



v 



15. What is the section modulus of a 10"x30.0 Ib. I beam 

 for an axis through its center of gravity parallel to the sides 

 of the web? 



16. If 16000 Ibs. per sq. in. is the working stress, what 



