# Design of RC Structures Questions and Answers – Neutral Axis of Beam Section

This set of Design of RC Structures Multiple Choice Questions & Answers (MCQs) focuses on “Neutral Axis of Beam Section”.

1. The neutral axis is the ______ axis of the equivalent section.
a) Centroidal
b) Positive
c) Negative
d) Equal area

Explanation: The neutral axis is the centroidal axis of the equivalent section.

2. Concrete is a material which is weak in _______
a) Compression
b) Strength
c) Tension
d) Plasticity

Explanation: Concrete is a material which is weak in tension, that is why it is used in the combination with steel as it is strong in tension.

3. What is the stress at the neutral axis of the beam?
a) 1
b) Positive
c) Negative
d) Zero

Explanation: The stress at the neutral axis of the beam is zero as there is neither compression nor tension.

4. As the loading on the stone arch changes, its neutral moves from its position.
a) True
b) False

Explanation: Stone is an inelastic medium, and has little strength in tension. Therefore the loading on the arch changes its neutral axis.

5. Find the neutral axis of the following figure.

a) 1
b) 1.5
c) 5
d) 0

Explanation: w1=3
w2=1
h1=1
h2=3
yn=[w1h1/2 + w2h2(h1+h2/2)]/{w1h1+w2h2}
= 1.5

6. In cantilever section, compression zone is above NA and tension zone is below NA.
a) True
b) False

Explanation: In simply supported section, compression zone is above NA and tension zone is below N, but in cantilever section, tension zone is above NA.

7. Where is the steel placed in simply supported member?
a) On the neutral axis
b) Above neutral axis
c) Below neutral axis
d) On centre of gravity

Explanation: Concrete is weak in tension so steel is provided in tension zone which is below the NA.

8. What will be the neutral axis constant for M15 grade of concrete and Fe250 grade of steel?
a) 0.4
b) 0.5
c) 1
d) 0

Explanation: k= mσcbc / (mσcbcst)
= (18.66*5) / (18.66*5 + 140)
= 0.4

9. What will be the lever arm constant for M20 grade of concrete and Fe415 grade of steel?
a) 0.29
b) 0.44
c) 1
d) 0.903

Explanation: k = 0.29
J = (1-k/3)
= (1-0.29/3) = 0.903

10. A beam having M20 and Fe415 grades has effective depth of 500mm. Find its critical depth of neutral axis.
a) 144.3
b) 150
c) 162.5
d) 123.1

Explanation: Xc / (d-Xc) = σcbc / (σst/m)
Xc / (500-Xc) = 7 / (230/13.33)
Xc = 144.3

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