Correct Answer - Option 2 : 15 mm
Explanation:
Nominal Cover to Meet Fire Resistance:
The nominal cover is the design depth of concrete cover to all-steel reinforcements.
It shall be not less than the diameter of the bar.
Minimum values of the nominal cover of normal-weight aggregate concrete to be provided to all reinforcement to meet the specified period of fire resistance shall be given in the table below
Member
|
Minimum Cover
|
Slab
|
20 mm
|
Beam
|
20 mm
|
Column
|
40 mm for d > 12 mm
25 mm for d < 12 mm
|
Footing
|
50 mm
|
Nominal Cover to Meet Durability Requirements:
Exposure |
Nominal concrete cover
(in mm) not less than
|
Mild |
20
|
Moderate |
30
|
Severe |
45
|
Very Severe |
50
|
Extreme |
75
|
Note:
For main reinforcement, up to 12 mm diameter bar for mild exposure the nominal cover may be reduced by 5 mm.