Minimum reinforcement in slabs in each direction Specify the minimum steel area in either direction as a percentage of the gross concrete section of the slab.

Introduction:
Minimum reinforcement controls cracking from shrinkage and temperature and ensures ductility even when applied loads are low. The requirement applies in each orthogonal direction of a reinforced concrete slab.

Given Data / Assumptions:

• Reinforced concrete slab with deformed (or mild) bars.
• Percentage calculated on gross concrete cross section.

Concept / Approach:

Typical code provisions specify minimum percentages. For slabs with mild steel, 0.15% is a common minimum; for high strength deformed bars, 0.12% may be permitted. The question asks for a conservative minimum figure suitable across cases.

Step-by-Step Solution:

Verification / Alternative check:

Check against bar spacing limits and cover; sometimes 0.12% is permitted with HYSD, but 0.15% remains a safe baseline.

Why Other Options Are Wrong:

0.75% is excessive for minimum steel; 0.10% and 0.12% can be insufficient or code-restricted depending on bar type; 0.20% is not the standard minimum.

Common Pitfalls:

Providing minimum percentage but violating maximum spacing; using large diameter bars at very wide spacing, which is less effective for crack control.

Final Answer:

0.15%