Purpose of lateral (transverse) reinforcement in R.C.C. columns: Which statement best captures a correct role of lateral reinforcement such as ties or spirals provided in reinforced concrete columns?

Introduction / Context:
Lateral reinforcement (ties or spirals) in R.C.C. columns provides confinement to the core concrete and restrains the main longitudinal bars. Proper detailing of ties is crucial for ductility, shear resistance, and to prevent bar instability under compression.

Given Data / Assumptions:

• Conventional reinforced concrete building columns.
• Standard tie detailing as per common codes.
• Focus on the primary structural role of lateral reinforcement.

Concept / Approach:
Under axial load and bending, longitudinal bars can buckle between tie nodes if not adequately restrained. Ties maintain bar spacing, prevent outward buckling, provide confinement (enhancing concrete strength/ductility), and assist in shear resistance via truss action around the core.

Step-by-Step Solution:
Identify the principal function: restrain longitudinal bars and confine concrete.Recognize secondary benefits: improved shear performance, delay of cover spalling.Check minimum diameters: many codes require ≥ 6 mm or ≥ 8 mm depending on steel type and bar size; 5 mm is usually below code minima.Therefore, select the clearly correct core statement (option a).

Verification / Alternative check:
Design standards emphasize prevention of bar buckling as the primary motivation for ties; confinement and shear capacity are well-documented additional advantages.

Why Other Options Are Wrong:

• b and c: Partially true as secondary effects, but the question asks for a correct role; (a) is the clearest primary function.
• d: “Not less than 5 mm” conflicts with common minima (often 6 mm or 8 mm), hence is incorrect as a universal rule.
• e: Since (d) is incorrect, “All the above” is also incorrect.

Common Pitfalls:
Assuming minimal tie diameter can be as low as 5 mm; ignoring code-specific minima and spacing rules can compromise column ductility and strength.

Final Answer:
Lateral reinforcement in R.C.C. columns is provided to prevent the longitudinal reinforcement from buckling