158 REINFORCED CONCRETE CONSTRUCTION 



a' s = cross-sectional area of compressive reinforcement. (Fig. 76). 



d' distance from the compressive face of the beam to the 

 plane of the compressive reinforcement. 



p f = ratio of cross-section of steel in compression to cross- 

 section of beam above the tensile steel = -,- 



bd 



f s = unit compressive stress in steel. 



Area of 



compressive 

 steel = a' s 



Area of 



tensile 

 steel a s 



Cross -section Stress Diagram 



FIG. 76. 



Then 



d) 



f'-fn 

 * *-J cn 



k = J2n(p+p' d '}+n 2 (p+p')*-n(p+p'') 

 V \ d ] 



M 



M e =bd%L and/ c =, in which 



M 9 =*bd 2 f s K and f s = , in which 

 d' k 2 k d' 



8 bd*L> 



M . . . , 

 > in which 



(2) 



(3) 

 (4) 

 (5) 

 (6) 

 (7) 

 (8) 



