Foundation types – grillage foundation basics: Which statements correctly describe a grillage foundation used under heavy isolated columns?
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AIt is commonly used for heavily loaded, isolated columns to spread the load at a shallow depth
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BIt is treated as a type of spread (shallow) foundation
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CIt consists of two or more layers of steel or timber beams placed at right angles to each other
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DAll of the above
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ENone of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Where soil near the surface has adequate bearing capacity but a pedestal footing would be too thick or inefficient, a grillage foundation provides economical load spreading for heavy columns, chimneys, or stanchions. It is widely used in steel construction and retrofits where shallow depth is preferred.
Given Data / Assumptions:
- Loads are predominantly vertical from isolated columns.
- Sufficient space exists to spread loads through multiple beam layers.
- Corrosion protection and concrete encasement are provided in practice.
Concept / Approach:A grillage is a spread foundation comprised of orthogonal layers of beams (steel or treated timber) embedded in concrete to distribute concentrated column loads over a wider area, reducing contact pressure on the soil. It is categorized under shallow foundations and designed to maintain acceptable settlement and bearing stresses.
Step-by-Step Solution:
Relate purpose: heavy load distribution at shallow depth.Classify: belongs to spread (shallow) foundation family.Describe construction: multiple beam tiers at right angles (grillage) encased in concrete.Hence, all listed statements are correct.Verification / Alternative check:Design guides show bearing pressure checks, beam bending and shear, and spacing to ensure concrete infill transfer and ease of placement.
Why Other Options Are Wrong:
- “None” contradicts standard practice descriptions; A–C are accurate.
Common Pitfalls:Ignoring corrosion protection for steel grillages; inadequate concrete cover; neglecting settlement compatibility when multiple columns are supported.
Final Answer:All of the above