Interaction diagram of a rectangular reinforced concrete beam-column is shown in Fig. with reference to this figure, which of the following statements in $$(a)$$ and in $$(b)$$ below are correct?

Let $$jd$$ be the lever arm between the resultant tensile force $$T$$ in the reinforcing prestressing steel and the resultant compressive force $$C$$ in concrete of a reinforced / prestressed concrete beam. When subjected to increase in the external bending moment, which one of the following statements is true in reinforced and prestressed concrete beams?

In reinforced concrete beams

Let $$jd$$ be the lever arm between the resultant tensile force $$T$$ in the reinforcing prestressing steel and the resultant compressive force $$C$$ in concrete of a reinforced / prestressed concrete beam. When subjected to increase in the external bending moment, which one of the following statements is true in reinforced and prestressed concrete beams?

In prestressed concrete beams

Which of the following Mohr's circles shown below qualitatively and correctly represents the state of plane stress at a point in a beam above the neutral axis, where it is subjected to combined shear and bending compressive stresses