Main reinforcement spacing in slabs: For a simply supported reinforced concrete slab, the centre-to-centre spacing (pitch) of main steel bars shall not exceed how many times the slab’s effective depth?

Introduction / Context:
Bar spacing limits in slabs prevent wide crack widths and ensure proper distribution of stress. Codes specify maximum spacing as a multiple of the effective depth and as an absolute value, whichever is smaller.

Given Data / Assumptions:

• Simply supported slab with main tension reinforcement.
• Standard code-type spacing rules applied.

Concept / Approach:
For main reinforcement in slabs, a common limit is: spacing ≤ 3 × effective depth (and also ≤ 300 mm as an absolute limit in many codes). These limits ensure adequate crack control and structural performance.

Step-by-Step Solution:
Identify the governing rule: spacing ≤ 3d (and ≤ 300 mm).Since the question asks “not exceed its effective depth by how many times,” choose 3 times.Hence, select “Three times the effective depth.”

Verification / Alternative check:
Typical slab detailing examples confirm that the 3d limit is standard for main bars in tension zones.

Why Other Options Are Wrong:

• 4d, 5d, 6d, 7d: exceed the usual code-prescribed limit for main reinforcement spacing.

Common Pitfalls:
Forgetting the absolute limit (e.g., 300 mm) in addition to the 3d rule; mixing distribution and main bar limits.

Final Answer:
Three times the effective depth