Question

The maximum spacing of 10 mm diameter bars in a reinforced concrete slab of 120 mm effective depth is

• A. 120 mm
• B. 240 mm
• C. 300 mm
• D. 360 mm

Hint:

Memorize the IS 456 rules for maximum bar spacing in slabs:
- Main Bars: Lesser of $3d$ or $300$ mm.
- Distribution/Temperature Bars: Lesser of $5d$ or $450$ mm.
These are very common questions in civil engineering exams.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the maximum permissible spacing for the main reinforcement bars in a reinforced concrete slab, according to codal provisions.

Step 2: Key Formula or Approach:
According to IS 456:2000 (Clause 26.3.3), the maximum horizontal spacing of the main tension reinforcement in a solid slab shall not exceed the lesser of the following two values:
1. Three times the effective depth of the slab ($3d$).
2. 300 mm.

Step 3: Detailed Explanation:
We are given:

• Effective depth ($d$) = 120 mm.

• The bar diameter (10 mm) is also given, but it does not affect the maximum spacing calculation for the main bars, only the minimum.


Let's calculate the two limits:
1. $3d = 3 \times 120 \text{ mm} = 360$ mm.
2. The absolute limit is 300 mm.
The maximum allowable spacing is the lesser of these two values.
\[ \text{Maximum Spacing} = \min(360 \text{ mm}, 300 \text{ mm}) = 300 \text{ mm} \]

Step 4: Final Answer:
The maximum spacing of the main reinforcement bars is 300 mm.