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PRACTICAL STRUCTURAL DESIGN 



For all woods other than long-leaf yellow pine the increases to 

 be one-half those given. The shearing stress, however, cannot 

 exceed one-tenth the fiber stress used for Class A structures. 



Building ordinances in American cities do not recognize any 

 difference hi allowable stresses dependent on the moisture contents, 

 so the fiber stresses permitted in cities apply to all structures. 

 It would be better if the city ordinance requirements were based 

 on Class D structures with proportionate decrease for structures 

 in other classes. 



The following table gives the allowable fiber stresses for wood 

 in the city of Chicago (1916). Each designer should use the stresses 

 permitted in the largest city nearest to the place where the building 

 is to be erected. 



The first column gives the name of the wood. The second column 

 gives the maximum bending fiber stress and this is the maximum 

 stress allowed if the wood is to be used as a tie in straight tension 

 something rarely possible because of the difficulty in making 

 proper connections so the nails, screws or bolts will properly trans- 

 mit the entire pull on the piece. 



The third column gives the compressive stress per square inch 

 on wood posts having a least breadth one-fifteenth the length. 

 For lengths greater than fifteen times the least dimension, the 

 compressive stress must be reduced, by a formula given in the 

 ordinance, long slender pieces bending under load and causing 

 additional strain on the concave side. 



The fourth column gives the allowable bearing stress per square 

 inch on the under side of a beam on the supports. The reaction 



