Difficulty: Easy
Correct Answer: 5 cm to 8 cm
Explanation:
Introduction / Context:
Ribbed slabs consist of closely spaced ribs with a thin topping slab forming the flange. The topping provides distribution of loads, diaphragm action, and a surface for finishes and services.
Given Data / Assumptions:
Concept / Approach:
A topping that is too thin may crack and fail to distribute loads; one that is too thick adds dead load without significant benefit. Practice typically adopts about 50–80 mm (5–8 cm) thickness for a good balance of performance and weight.
Step-by-Step Solution:
Identify typical topping thickness used in ribbed slabs.Select the 5–8 cm range as most common in building practice.Confirm that this thickness allows cover to reinforcement, conduits, and finishing layers.
Verification / Alternative check:
Structural detailing manuals and manufacturer guidance for joist systems commonly specify a minimum topping thickness in the 50–80 mm range.
Why Other Options Are Wrong:
Common Pitfalls:
Forgetting to include screed/finish thickness in dead load; using too thin a topping over deep rib spacing causing localized punching or cracking.
Final Answer:
5 cm to 8 cm
Discussion & Comments