REINFORCED CONCRETE 321 



Notation. The accompanying illustration shows a section of 

 a reinforced-concrete beam. The following notation is used 

 for the different elements involved I 



in its design: p- 



6 = width of beam, in 



inches; 

 d = effective depth 



= distance of steel 





from top of beam ; 



x=kd distance of neu- 

 tral axis from top 

 of beam; 



Cenfer of 



Concrefe 



A/eufra//l 



Mf 



7T 

 i 



= arm of stress couple = distance between center 

 of steel and center of concrete; 



A = total area of steel ; 



p = steel ratio = ; 

 bd 



p e = economic steel ratio; 

 M bending moment; 



fs and f c = stresses in steel and concrete, respectively, 

 actually produced by the bending moment 

 M; 

 F s and FC^ maximum allowable unit stresses in steel and 



concrete, respectively; 



Jfrf s and M c = working moment of resistance of steel and con- 

 crete for the unit stresses F s and F c , respec- 

 tively; 



r = stress ratio =f s : f c ; 

 r e = stress ratio when economic percentage of steel 



is used, which is equal to F s : F f ; 

 E s and EC = moduli of elasticity of steel and concrete, 



respectively; 

 E s 



