172 REINFORCED CONCRETE CONSTRUCTION 



axes which are perpendicular to the one first considered. Thus, if 

 the material of a column is held laterally, then lateral compressive 

 stresses are developed which tend to neutralize the effect of the 

 longitudinal compressive stresses and thus to increase the 

 resistance against failure. This is the principle involved in 

 the spiral or banded column. Fig. 80 shows a spiral form of 



spaci 

 H 





FIG. 79. 



FIG. 80. 



FIG. 81. 



reinforcement. Longitudinal crimped spacing bars serve to 

 maintain a uniform pitch. Banded reinforcement is similar 

 to that shown in Fig. 79 with the exception that the clear spacing 

 of the bands to be effective must not be greater than about 

 one-fourth the diameter of the enclosed column. The same 

 limit as regards spacing applies to spirals. 



The yield-point is taken to be the point on the stress-defor- 



