When the cross-sectional size of a reinforced concrete column is reduced above a floor level, how should the main longitudinal bars be handled across that level to ensure continuity and safe force transfer?

Introduction / Context:
Column size transitions are common for architectural or load-path reasons. Proper continuity and anchorage of longitudinal bars across the step are crucial to ensure axial load transfer, bending continuity, and confinement compatibility.

Given Data / Assumptions:

• Column size reduces at a floor level.
• Need a detailing strategy for main reinforcement across the step.
• Lap length and confinement must satisfy code requirements.

Concept / Approach:
There are multiple acceptable methods provided they meet development length, splice, and bend radius requirements. Options include: (1) continuing bars straight through into the upper column, (2) bending bars inward with adequate radius and cover to match the smaller core, or (3) stopping bars and providing properly lapped starter bars above with sufficient confinement via ties.

Step-by-Step Solution:
Choose a method based on congestion, cover, and practicality.If bending inward, ensure bend diameter, cover, and no sharp kinks.If lapping, provide lap length ≥ required development length in compression/tension as applicable and within a well-tied splice region.Maintain continuity of ties/links across the transition zone.

Verification / Alternative check:
Design checks must confirm that the splice zone has adequate confinement (closer tie spacing) and that the lap length satisfies bar grade, concrete strength, and bond conditions.

Why Other Options Are Wrong:
Each single option alone may be correct in some scenarios; the best answer encompasses all permissible approaches with correct detailing. Hence the comprehensive choice is preferred.

Common Pitfalls:
Insufficient lap length, inadequate tie spacing in splice zones, and cover violations when bars are bent sharply to fit upper dimensions.

Final Answer:
All the above can be used with proper detailing.