# Design of RC Structures Questions and Answers – Circular Slabs

This set of Design of RC Structures Multiple Choice Questions & Answers (MCQs) focuses on “Circular Slabs”.

1. Which of the following is not a function of a circular slab?
a) Roof of a circular auditorium
b) Floor of circular water tank
c) Roof of round pump house

Explanation: The function of a circular beam is mainly to work as a floor or roof of a circular structure. Sun shade is completely a rectangular one-way slab. Therefore a sunshade cannot work as a sunshade anyway.

2. In the circular slab the reinforcement is provided in the form of __________
a) tie
b) longitudinal bar
c) transverse bar
d) mesh

Explanation: The reinforcement should be given in two directions i.e. i. Circumferential ii.radial and this may result in anchorage and congestion issue. Therefore the reinforcement is given in the form of mesh.

3. If a circular slab of 5m radius is loaded with 3kN/mudl, what is the highest value of radial bending moment?
a) 14.0625 kNm
b) 16.0625 kNm
c) 20 kNm
d) 21 kNm

Explanation: According to calculation the radial bending moment is calculated to attain the highest value at the midpoint and the value is = 3*w*a2/16
w = udl applied; a=radius of the slab;
M=3*3*5*5/16 = 14.0625 kNm.

4. For a circular slab of 10m diameter and freely supported at edges and loaded with 3 kN/m, what is the value of the radial shear force?
a) 7.5 kNm
b) 10 kNm
c) 20 kNm
d) 15 kNm

Explanation: By calculation we get the value of radial shear force is = w*r/2;
w = udl applied; r = radius;
F = 3*5/2=7.5 kN.

5. A circular slab fixed at edges and carrying udl the point of contraflexure w.r.t. radial moment occurs at .577a distance from the centre.
a) False
b) True

Explanation: For a circular slab the radial moment changes its sign at .577a from the centre, therefore it is the point of contraflexure.

6. What is the value of maximum radial moment for fixed circular slab of 5m diameter carrying 6 kN/m?
a) 2.34 kNm
b) 4.68kNm
c) 5 kNm
d) 6 kNm

Explanation: According to calculation the radial bending moment is calculated to attain the highest value at the support and the value is = 2*w*a2/16(negative)
w = udl applied; a=radius of the slab;
M=2*6*2.5*2.5/16= 4.68kNm.

7. What is the value of maximum circumferential moment for fixed circular slab of 5m diameter carrying 6 kN/m?
a) 2.34kNm
b) 4.68kNm
c) 7kNm
d) 9kNm

Explanation: According to calculation the radial bending moment is calculated to attain the highest value at the support and the value is = 1*w*a2/16(positive)
w = udl applied; a=radius of the slab;
M = 1*6*2.5*2.5/16 = 2.34kNm.

8. If a slab of 4m radius is simply supported at edges and load 6kN is distributed along the circumference what is the radial shear force per unit width?
a) 249N
b) 239N
c) 259N
d) 270N

Explanation: The formula for the radial force is = W/(2*3.14*4)
=6000/(2*3.14*4)=239kN.

9. The column is situated at the centre of the circular slab.
a) False
b) True

Explanation: The circular slab is mainly supported by the column at the centre. At the edges various kinds of support may occur such as simply support or fixed edges etc.

10. What is the biggest issue in providing reinforcement in circular slab?
a) Shear reinforcement cannot be provided
b) Requirement of steel is very high
c) Congestion issues
d) Scheduling of the bar bending

Explanation: The reinforcement should be given in both radial and circumferential direction of the circular slab as bending moment in both cases exists. Therefore congestion is the main issue in circular slab.

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