In flat slab (beamless) construction used in reinforced concrete buildings, the slab is primarily supported by which structural element(s)? Choose the most accurate statement about the support system.

Introduction / Context:
A flat slab system eliminates downstand beams; loads are transferred directly from the slab to columns through column capitals and/or drop panels. Understanding the support mechanism is fundamental for punching shear checks, detailing, and service integration.

Given Data / Assumptions:

• Beamless slab system (flat slab) in reinforced concrete.
• Slab cast monolithically with columns and, where required, drop panels or column heads.

Concept / Approach:
By definition, a flat slab is supported directly on columns (and sometimes on shear heads/column capitals) without intermediate beams. Monolithic casting ensures composite action and enables direct load path to the columns while controlling punching shear with drops or shear reinforcement.

Step-by-Step Solution:
Identify structural system: beamless slab connected to columns.Confirm monolithic construction to ensure proper transfer and continuity.Hence, support is ‘‘on columns monolithically built with the slab’’.

Verification / Alternative check:
Design procedures for flat slabs focus on column-strip and middle-strip moments and punching shear at column faces—further evidence that beams are not the primary supports.

Why Other Options Are Wrong:

• On beams / on beams and columns: contradicts the beamless nature of flat slabs.
• On columns (generic): close, but omits the essential monolithic behavior emphasized in design practice.
• All the above: incorrect because beams are not part of the system.

Common Pitfalls:
Assuming beam action in a flat slab; neglecting punching shear; forgetting that drops/column heads modify stiffness and moment distribution.

Final Answer:
on columns monolithically built with the slab