In reinforced concrete beams, bars are not to be bundled in direct contact if the bar diameter exceeds which limit?

Introduction / Context:
Bundling reinforcement bars in contact can ease congestion and placement, but beyond a certain diameter it impedes concrete flow and cover reliability, increasing risks of voids, honeycombing, and poor bond. Hence, codes limit the diameter for which in-contact bundling is permitted.

Given Data / Assumptions:

• Member: RC beam.
• Practice: bundling several tension bars in contact.
• We seek the maximum diameter at which this is allowed.

Concept / Approach:

Larger single bars have bigger ribs and greater spacing demands. When bundled in contact, the interstices can obstruct aggregate and cement paste flow, degrading compaction. A conventional upper limit around 36 mm is therefore enforced for in-contact bundling.

Step-by-Step Solution:

Verification / Alternative check:

Alternative detailing strategies for larger reinforcement include using multiple smaller bars, staggering layers, or increasing member width to maintain spacing and cover, avoiding the need for oversized bundles.

Why Other Options Are Wrong:

• 12/20/30/35 mm: Either too restrictive or slightly below the conventional cap; 36 mm is the recognized threshold.

Common Pitfalls:

• Bundling large bars in narrow beams leading to compaction defects.
• Ignoring minimum clear spacing and cover when forming bundles.

Final Answer:

36 mm