Serviceability guideline: What is the maximum recommended span-to-effective-depth (L/d) ratio for a cantilever RCC slab, as a quick preliminary sizing rule?

Introduction / Context:Preliminary proportioning of RCC slabs uses empirical span-to-depth ratios to control deflection without detailed analysis. Cantilever slabs are more flexible and therefore have stricter (smaller) L/d limits than simply supported or continuous slabs.

Given Data / Assumptions:

• Member type: reinforced concrete cantilever slab.
• Objective: quick sizing for serviceability control.
• Normal materials and detailing; modification factors may apply later.

Concept / Approach:Standard practice adopts basic L/d limits. For slabs, typical base limits are roughly: cantilever ≈ 10, simply supported ≈ 20, continuous ≈ 26 (subject to code-specific modification factors for tension steel, compression steel, and span). The smaller limit for cantilevers reflects higher deflection sensitivity due to the fixed-free boundary condition.

Step-by-Step Solution:Identify member as a slab cantilever → use stricter L/d.Adopt the basic value L/d ≈ 10 for preliminary depth selection.Adjust later with code modification factors if required.

Verification / Alternative check:Comparing with beams: cantilever beams are typically limited near 7; slabs permit larger L/d than beams for similar control because slab action distributes stiffness in the width. Hence 10 is a practical slab value.

Why Other Options Are Wrong:8: Conservative but below common slab guideline; may lead to uneconomical depth.12, 14, 16: Too slender for a cantilever slab at preliminary stage; risk of excessive deflection.

Common Pitfalls:

• Confusing slab and beam limits; slab limits are generally higher (slenderer).
• Forgetting to check deflection explicitly when spans are long or loads are high.

Final Answer:10