44 STRENGTH OF MATERIALS 



Consequently, the intensity of the fiber stress can be considere-l t,, 

 vary directly as its distance from the neutral axis over t 

 cross section of the beam, provided the area of the steel is increase 

 in the ratio |- If, then, the depth is kept constant, the breadt 

 art be increfsed in this ratio, and the cross section thus obtained 



IT 





1 



FIG. 28 



wul appear as shown in Fig. 28. Therefore, if / f denotes the iimim-nt 

 of inertia of this modified section, the stress in the extreme fiber is 

 given by the formula 



P = 



.--<-, 



FIG. 29 





Problem 49. A rectangular concrete beam 14 in. deep and 8 in. wide is r- 

 by two f-in. square steel rods placed 1 in. from the bottom, as shown 

 Assuming that the ratio of the moduli of elasticity of sUn-1 and coiicr- 

 -E 1 ., : E c = 15 : 1, find the moment of inertia of a cross section of the beam al> 

 gravity axis parallel to the base. 



Solution. Increasing the area of the steel in the rate 16 : 1, it becomes 16.0 in.*. 

 The area of the concrete included in the same horizontal strip with the steel is 



