Minimum clear spacing for horizontal parallel bars (same diameter):\nWhen horizontal reinforcement bars of the same size are placed side-by-side in one layer, the minimum clear spacing should not be less than…

Introduction / Context:
Minimum bar spacing requirements ensure adequate concrete flow, proper compaction, and reliable bond. Insufficient spacing can cause honeycombing, poor aggregate accommodation, and reduced development of reinforcement strength.

Given Data / Assumptions:

• Bars are of equal diameter placed in the same layer.
• We are addressing minimum clear spacing (not center-to-center spacing).

Concept / Approach:
A common rule in RC codes is that clear spacing between parallel bars shall be at least the bar diameter, while also not being less than a value related to the maximum aggregate size (e.g., 5 mm more than nominal maximum aggregate size) and a small absolute minimum (e.g., 25 mm) where applicable. For same-size bars, the bar-diameter criterion is the primary rule cited in such objective tests.

Step-by-Step Reasoning:
Identify the governing minimum: clear spacing ≥ bar diameter.Check aggregate size requirement separately during detailed design.

Verification / Alternative check:
Site experience confirms that spacing less than one diameter leads to poor concrete flow and increased risk of voids, which is unacceptable for durability and bond.

Why Other Options Are Wrong:
Values such as 2.5d, 3d, etc., may be used in specific detailing or bundled bars, but the basic minimum for same-diameter parallel bars in a layer is one diameter.

Common Pitfalls:

• Confusing clear spacing with centre-to-centre spacing.
• Neglecting aggregate size checks that can govern in some mixes.

Final Answer:
one diameter