This set of Design of RC Structures Multiple Choice Questions & Answers (MCQs) focuses on “Axially Loaded Columns – Cover to Reinforcement”.
1. What is the definition of cover of a reinforcement?
a) The thickness of the steel surrounding the reinforcement
b) The thickness of the concrete surrounding the reinforcement bars
c) The thickness of an external material over the concrete
d) The thickness of the reinforcement
View Answer
Explanation: The thickness of the concrete surrounding or at the bottom or at the top of the reinforcement bar is called the cover. The minimum cover should be provided for any reinforcing structures as mentioned in clause 26.4 of code IS 456:200.
2. What is the function of the cover?
a) To protect reinforcement bar from external factors
b) To protect reinforcement bar from creep
c) To protect reinforcement bar from buckling
d) To protect reinforcement bar from lateral movement
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Explanation: The concrete cover is mainly provided to satisfy the durability issues from several environmental factors. Again in Table 16B of clause 26.4.2 of code IS 456:2000 the fire resisting function of clear cover is mentioned.
3. What should be the nominal cover for a longitudinal reinforcement for a column?
a) 20mm
b) 40mm
c) 25mm
d) 50mm
View Answer
Explanation: According to recommendation of IS 456:2000 the nominal cover for a column should be 40mm. Remaining 20mm, 25mm, 50mm are for slabs, beams & footings respectively.
4. What is the minimum cover thickness for a slab in a moderate weather?
a) 30mm
b) 40mm
c) 20mm
d) 10mm
View Answer
Explanation: IS 456:2000 gives (Table 16A ,clause 26.4.2) the minimum cover thickness for slab in moderate condition is 30mm. The minimum cover thickness for slab in dry weather condition is 20mm.40mm clear cover is given for columns usually.
5. If the clear cover is 40mm and 8 mm dia stirrup and 4 numbers of 20mm dia bars as main reinforcement is given, what is the effective cover?
a) 78mm
b) 68mm
c) 88mm
d) 58mm
View Answer
Explanation: According to codal provision,
Effective cover=clear cover+(dia of the shear reinforcement bar)+(dia of the main reinforcement bar/2)
=40+8+(20/2)=58mm
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