172 ILLINOIS ACADEMY OF SCIENCE 



stant between the tenth and eleventh floors, whereas the mo- 

 ment varies and passes through zero at the point of contra- 

 rlexure. 



If the columns in the story just below the tenth floor are 

 divided at the point of contra-flexure the lower portion of 

 each column will exert upon the upper portion a shear, but 

 no moment. These shears are represented by Rj, R 2 , R 3 and 

 R 4 . Likewise if each girder is divided at its point of contra- 

 flexure each part would exert upon the other part a shear, but 

 no moment. 



If the dimensions of a building are known and a wind pres- 

 sure, for the purpose of design, is assumed, the total shear 

 upon each story of the building can be determined. If there- 

 fore the distribution among the columns of the total shear 

 upon a story is known, and the location of the point of contra- 

 flexure of all members is known, the bending moment in the 

 columns and girders can be determined. Unfortunately, 

 however, the exact mathematical determination of the above 

 quantities is very long and complicated. 



While some effort has been made to devise an exact an- 

 alysis of the wind stresses in the steel frames of office 

 buildings, 1 designers of buildings for the most part, have been 

 content to use approximate methods. 



Four approximate methods have been used. For conveni- 

 ence in reference these will be designated as Method I, Method 

 II. Method II and Method IV, respectively. Mr. R. Fleming 

 presented the first three methods in Engineering News. 2 

 These methods, as applied to a building in which all columns 

 of a story have the same section, are based upon the following 

 assumptions : 



ASSUMPTIONS IN METHOD I 



1. A bent of a frame acts as a cantilever. 



2. The point of contra-flexure of each column is at mid- 

 height of the story. 



J Wind Stresses in the Frames of Office Buildings, by Albert Smith, Journal 

 Western Societv of Engineers, Vol. XX, No. 4, p. 341. 



Stresses in Tall Buildings, by Cyrus A. Melick, Bulletin No. 8, College of En- 

 gineering, University of Ohio. 



The Theory of Frameworks with Rectangular Panels and Its Application to 

 Buildings which have to Resist Wind, by Ernst F. Jonson, Tran. Am. Soc. C. E., 

 Vol. 55, p. 413. 



2 Wind Bracing Without Diagonals for Steel-Frame Office Buildings, Engineer- 

 ing News, March 13, 1913. 



