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5-question demo · FCI Assistant Grade III - Civil Engineering - RCC Designs

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Question 1 of 5
In a reinforced concrete beam under bending, the neutral axis is the line or plane where:
A A. Tensile stress is maximum
B B. Compressive stress is maximum
C C. Strain is zero and no stress develops
D D. Shear stress is maximum
Why: The **neutral axis** is the longitudinal axis in a beam where the **longitudinal stress** and **strain** are both zero during bending. Above the neutral axis, the beam is in **compression**, and below it, the beam is in **tension**. This concept is fundamental to flexural strength analysis in RCC design, as it divides the cross-section into tension and compression zones for stress distribution calculations[1][2]. Option C correctly identifies this property.
Question 2 of 5
The flexural strength of plain concrete is primarily determined by: A. Compressive strength of concrete B. Tensile strength of concrete C. Shear strength of concrete D. Bond strength between concrete and steel
A A. Compressive strength of concrete
B B. Tensile strength of concrete
C C. Shear strength of concrete
D D. Bond strength between concrete and steel
Why: **Flexural strength** of concrete is its ability to resist **failure in bending**, which is governed by its **tensile strength** since concrete fails in tension under flexural loading. The empirical relationship is \( f_{cr} = 0.7 \sqrt{f_{ck}} \) MPa, where \( f_{ck} \) is the characteristic compressive strength. Compressive strength indirectly determines flexural strength through this correlation[1][2]. Option B is correct.
Question 3 of 5
The flexural strength \( f_{cr} \) of concrete can be estimated from its characteristic compressive strength \( f_{ck} \) using the expression given in IS 456. What is the formula?

(A) \( f_{cr} = 0.7 \sqrt{f_{ck}} \)
(B) \( f_{cr} = 0.7 f_{ck} \)
(C) \( f_{cr} = 0.7 f_{ck}^{0.5} \)
(D) \( f_{cr} = 0.7 f_{ck}^{1/3} \)
A \( f_{cr} = 0.7 \sqrt{f_{ck}} \)
B \( f_{cr} = 0.7 f_{ck} \)
C \( f_{cr} = 0.7 f_{ck}^{0.5} \)
D \( f_{cr} = 0.7 f_{ck}^{1/3} \)
Why: According to IS 456 (cl. 6.2.2), the flexural strength \( f_{cr} \) is given by \( f_{cr} = 0.7 \sqrt{f_{ck}} \) in N/mm², where \( f_{ck} \) is the characteristic compressive strength. This empirical relation estimates the modulus of rupture from cube strength. Option A matches this formula exactly. Options B, C, and D use incorrect exponents or multipliers[2].
Question 4 of 5
What is the primary significance of flexural strength in RCC beams?
A It determines the beam's ability to resist shear forces
B It indicates the beam's capacity to resist bending moments without failure
C It measures the compressive strength of concrete
D It defines the bond strength between steel and concrete
Why: Flexural strength indicates the capacity of an RCC beam to resist bending moments and avoid failure under flexure.
Question 5 of 5
Flexural strength of an RCC beam is primarily influenced by:
A The tensile strength of steel reinforcement
B The compressive strength of concrete
C The bond strength between steel and concrete
D The shear strength of concrete
Why: Flexural strength depends mainly on the compressive strength of concrete as it resists compressive stresses in bending.