Slab–column interaction (transverse bending zone): The plan extent of the zone where significant transverse bending of a slab is likely near a column face can be obtained by drawing lines from the column faces at what inclination θ to the horizontal?

Introduction / Context:
Near slab–column connections, load transfer and bending are three-dimensional. Designers often identify an influence or dispersion zone emanating from the column faces to approximate where higher bending effects occur and to guide reinforcement placement, punching checks, and detailing.

Given Data / Assumptions:

• Flat slab or slab supported on columns.
• Identification of a simplified dispersion zone.
• Guidance for preliminary detailing and checking.

Concept / Approach:
A commonly used dispersion angle in practice-oriented problems is 45°. Projecting 45° lines from column faces provides a practical estimate of the area influenced by high transverse bending and shear, aiding placement of top steel around columns and informing punching shear perimeters (which themselves are defined by code, e.g., at a distance of d/2 from the loaded area).

Step-by-Step Reasoning:
Mark the column perimeter in plan.From each face, project lines at 45° to identify the critical bending region.Ensure adequate top reinforcement and anchorage within this zone and check punching shear independently.

Verification / Alternative check:
Advanced analysis (e.g., finite-element plate models) yields a similar qualitative influence region radiating from column faces; 45° is a reasonable simplified envelope for routine detailing guidance questions.

Why Other Options Are Wrong:
30° or 60°: These are not the standard simplified dispersion angles used in such MCQs.None of these: A simple and widely recognized angle exists for this purpose.

Common Pitfalls:

• Confusing this detailing cue with the exact code-defined punching critical perimeter (at distance d/2).
• Neglecting to provide sufficient top steel cages around columns.

Final Answer:
45°