Question

Consider the following statements:
Under-reinforced concrete flexural members
1. are deeper
2. are stiffer
3. can undergo larger deflection
Which of these statements is/are correct?

• A. 1,2 and 3
• B. 1 and 3
• C. 2 only
• D. 1 and 3

Answer 1

The correct option is A 1,2 and 3

The stiffness of a flexural member $\propto \frac{EI}{L}$
For deeper section, the moment of inertia (I) will be more and so stiffness will also be more. Further for under reinforced sections $x_u<x_{u,max}$ means that less concrete under compression and therefore it requires deeper sections to resist a given moment.
$M_r=Rb{d}^2$
where $R<R_c$ (for balanced section)(