Composite (cased) beams – when is a steel beam treated as a cased beam? Under what conditions is a rolled steel beam treated as a cased beam in concrete for design and detailing purposes?

Introduction / Context:
Encasing a steel beam in concrete improves fire resistance, stiffness, and durability, and can enhance composite action when detailed properly. Codes outline when a member may be treated as a cased beam.

Given Data / Assumptions:

• Rolled steel beam intended to be encased in concrete.
• Concrete provides protection and potential stiffness benefits.
• Dimensional and detailing requirements must be met.

Concept / Approach:
A member is considered a cased beam if both geometry and encasement meet minimum limits. Typical conditions include minimum gap in double-channel sections, overall size limits to ensure proper casing, encasement strength and aggregate considerations, and adequate concrete cover beyond flanges for protection.

Step-by-Step Solution:

Verification / Alternative check:
Details are in classic composite/cased-beam provisions and standard exam references; fulfilling all ensures the member performs as a cased beam.

Why Other Options Are Wrong:
Each single statement corresponds to a valid requirement; hence the comprehensive choice “All the above” is correct.

Common Pitfalls:
Insufficient concrete cover; inadequate connector detailing; assuming composite action without shear connectors where required.

Final Answer:
All the above