Grillage foundations (steel): The clear distance between the flanges of adjacent grillage beams is generally kept…

Introduction / Context:
Grillage foundations use tiers of steel beams encased in concrete to spread heavy column loads over soils with limited bearing capacity. Proper spacing of beams controls concrete confinement, shear transfer, and ease of concreting while minimizing steel usage.

Given Data / Assumptions:

• Steel grillage with flanged sections (e.g., I-beams).
• Beams arranged in one or more tiers and embedded in concrete.
• Objective: achieve uniform load dispersion and adequate concrete flow between beams.

Concept / Approach:
A practical rule is to keep the clear spacing between adjacent flanges approximately equal to the flange width. This spacing balances two needs: sufficient concrete between beams for effective load sharing and encasement, and compact footprint to limit foundation size. Too little spacing hampers concrete placement and creates weak planes; too much spacing wastes plan area and can lead to uneven stress distribution in the concrete mass.

Step-by-Step Solution:
Relate beam geometry to concrete flow requirements.Apply the spacing rule-of-thumb: clear gap ≈ flange width.Ensure adequate cover and shear keys per detailing standards.Select “Equal to the flange width.”

Verification / Alternative check:
Standard detailing guides and BOQ descriptions for steel grillage typically specify clear spacing equal to flange width (subject to minimum cover and constructability checks).

Why Other Options Are Wrong:
Fixed 40 cm: Not universally appropriate; depends on section size.Twice or half flange width: Either spreads too far or too close for general practice.“Maximum of …”: Not a design principle.

Common Pitfalls:
Ignoring concrete cover and compaction clearances; forgetting that unequal spacing may cause uneven load transfer.

Final Answer:
Equal to the flange width.