Grillage foundation detailing — minimum 15 cm cover location In steel grillage foundations, a minimum concrete cover of about 15 cm is typically provided at which location to protect the steelwork?

Introduction / Context:
Grillage foundations distribute heavy column loads to soil using tiers of steel beams encased in concrete. Adequate concrete cover is crucial to protect steel against corrosion and to ensure proper load transfer and durability, especially at vulnerable edges and ends where exposure risk is higher.

Given Data / Assumptions:

• Steel grillage with upper and lower tiers embedded in concrete.
• Protection against corrosion and adequate confinement are required.
• Typical detailing practices from building foundation handbooks are considered.

Concept / Approach:
Covers are provided on all faces; however, a commonly cited detailing requirement is to ensure not less than about 15 cm of concrete cover at the ends of external beams to fully enclose and protect the steel. This generous cover at ends helps mitigate edge effects, accommodate anchorages, and protect against moisture ingress. Other faces may use different minimums depending on specifications, but the emphasized requirement at beam ends is widely adopted.

Step-by-Step Solution:

Verification / Alternative check:
Detailing sketches in standard texts and codes of practice show larger covers at edges/ends compared with internal faces to ensure durability and constructability.

Why Other Options Are Wrong:

• upper flange of the top tier: May require cover, but the specific 15 cm minimum is associated with beam ends.
• lower beam of the lower tier: Bottom cover is provided but commonly specified differently.
• none of these/all of these: Do not match the emphasized location for the given minimum.

Common Pitfalls:
Underestimating cover at beam ends; neglecting drainage and protective coatings; forgetting that cover requirements can vary by specification and environment.

Final Answer:
ends of the external beams