'Waffle slabs' (ribbed in two directions) are preferred when:
Choose the correct answer
Short spans < 3 m (standard rooms)
Long spans (8–15 m) where weight reduction is critical — voids reduce dead load while maintaining stiffness
Underwater structures only
All spans — no restrictions
Correct Answer
B. Long spans (8–15 m) where weight reduction is critical — voids reduce dead load while maintaining stiffness
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Waffle slab (two-way ribbed): solid topping + thin ribs in two directions + voids (dome formwork). Benefits: (1) Large spans (8–15 m) with lower dead load (30–50% lighter than solid slab); (2) Flat soffit aesthetics. Limitations: complex formwork, higher cost than solid slab for short spans. Solid panels around columns for punching shear resistance. Used in: auditoriums, long-span commercial floors.
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