92 



Allowable Unit Stresses for Timber Columns in Accord- 

 ance with tlie Buildinu Laws of Boston and Chicago. 



FOR POSTS WITH FLAT ENDS. 



The stresses given in the following table, in which L=Length 

 of post, D= Least diameter of post, and S= Stress per sq. in. 



For information not given in these tables, see Complete 

 Building Laws of the Various Cities. 



GENERAL RULE FOR THICKNESS OF WALLS. 

 (Kidder). 



An approximate rule for mercantile buildings four or 

 more stories in height is here given: 



In buildings of brick, such as is used in Boston or 

 Chicago, the thickness of the walls should increase from 

 the top down in series of 3 stories in the following ratio: 

 The top three stories should be 16 in. thick; the next 

 series, 20 in.; the next, 24 in.; the next, 28 in. For an 

 inferior grade of brick the two upper stories only should 

 be 16 in., the succeeding series of three increasing in the 

 same ratio as the above. 



In" buildings less than 5 stories, a thickness of 12 in. 

 for the upper story Is allowable. 



In specifying the thickness of walls the following should 

 be kept in mind: First, walls of buildings intended for 

 warehouses or mercantile use, should be thicker than 

 those of office or apartment buildings; second, thicker 

 walls are required for high stories and clear spans ex- 

 ceeding 25 ft.; third, the thickness should be increased 



