Minimum number of longitudinal bars in reinforced concrete columns: Select the correct set of minimum bar counts for typical column shapes used in building frames.

Introduction / Context:

Minimum numbers of longitudinal bars in RC columns ensure adequate confinement by ties/spirals and proper distribution of reinforcement around the perimeter, improving ductility and resistance to buckling between restraints.

Given Data / Assumptions:

• Standard building columns (rectangular, circular, polygonal).
• Minimum bar counts per common code practice.

Concept / Approach:

For rectangular columns, at least 4 bars (one near each corner) are required. For circular columns with ties/spirals, at least 6 bars provide uniform distribution. For octagonal or other polygonal sections, at least 8 bars are customary to maintain spacing and confinement efficiency.

Step-by-Step Solution:

Verification / Alternative check:

Detailing guides in RC design confirm these minima to avoid large bar spacing and ensure effective confinement.

Why Other Options Are Wrong:

• Individual statements a–c are true; thus “all the above” is the most complete choice.
• “None” contradicts established practice.

Common Pitfalls:

• Counting total bars without checking spacing and cover limitations; both constraints also govern final layouts.

Final Answer:

all the above