290 CONCRETE DESIGN 



This stress is larger than the allowable stress, which shows 

 that the column section selected is too small. If a section 

 31 in. in diameter is assumed, then, 



A = .7854X31- = 754.77 sq. in. 

 Substituting in the formula, 



200,000 8X4X100,000 



- WJ7* 754.77X31 "* "" P " ^ ta 



Since this is less than 417 lb., a column of this diameter 

 is safe. 



In a fire, a column is apt to be injured by the heat to a 

 distance below the surface of 1J in. Therefore, in design- 

 ing columns by the preceding methods, 1 in. should be 

 added all around the column proper. 



REINFORCED CONCRETE 



BEAMS 



The design of reinforced concrete is not an exact science. 

 The majority of the recommendations and formulas herein 

 given are taken from the excellent report of the "Joint 

 Committee." The Joint Committee is a committee of mem- 

 bers of the American Society of Civil Engineers, the 

 American Society for Testing Materials, the American Engi- 

 neering and Maintenance of Way Association, and the 

 Association of American Portland Cement Manufacturers 

 formed "for the purpose of investigating current practice 

 and providing definite information concerning the properties 

 of concrete and reinforced concrete." 



Only Portland cement is suitable for reinforced concrete. 



The aggregate is divided into two classes, namely, fine 

 and coarse. Fine aggregate consists of sand, crushed stone, 

 or gravel screenings, and which, when dry, passes through a 

 screen having holes i in. in diameter. Coarse aggregate 

 consists of crushed stone or gravel which is retained on a 

 screen haying holes i in. in diameter, but which passes 

 through a screen having holes 1 in. in diameter or smaller. 

 In both fine and coarse aggregates, a gradation of size of the 

 particles is generally desirable. 



