Fig. 4-11 Effect of increasing tension steel area, $A_s$.
also increases the elastic stiffness of the section, because the section moment of inertia is significantly affected by the depth of the section. These results clearly indicate the importance of the effective flexural depth of a member, so proper placement of reinforcement during construction should be a priority item for field inspectors.
Changes in concrete strength and section width have a smaller effect on moment strength than might be initially expected. These two variables will have only a small
Fig. 4-12 Effect of increasing $f_y$, $d$, $f_c'$, $b$, and $A_s'$.