COLUMNS 



171 



or else the diameter of the sleeve should not be over 1/16 in. 

 larger than the diameter of the rod. All such splices should 

 be made above the floor level but not more than 12 in. above 

 the same. When small diameter rods are used, say up to 1 1/4 

 in., joints in the vertical steel may be provided for by over- 

 lapping - a sufficient distance to develop the requisite bond 

 strength, and the lapped rods should be securely wired or bolted 

 to each other. It is much better to avoid splices in a column 

 between lateral supports. In footings where the length of 

 embedment is not sufficient to take all the stress, large rods 

 (or shapes) should rest upon suitable base plates in the foun- 

 dation concrete. 



The economy of steel reinforcement is dependent upon the 

 working stresses permissible in the concrete and the value of 



n } since the stress in the steel =f c n. The following table gives 

 p 



the various values of -r and f a for different stresses in the concrete 



A. 



and different moduli of elasticity: 



It should be noted in the table that the stresses in the steel 

 will be relatively low except in the unusual combination of 

 high working stresses in the concrete with large value of n. 



66. Columns with Hooped Reinforcement. Whenever a 

 material is subjected to compression along one axis, then, as 

 a consequence, there will be an expansion of the material along 



