A simply supported RCC one-way slab for an office floor has clear dimensions of 4 m × 10 m with 230 mm walls all-around. What is the effective length of the slab? (Take the effective depth of the slab as 160 mm)
- A2.23 m
- B4.16 mCorrect
- C6.84 m
- D10.23 m
Solution
Concept
The effective span of a simply supported slab is the lesser of (clear span + effective depth) and (centre-to-centre distance of supports).
Formula
Leff = min(Lclear + d, Lc/c)
Step-by-step solution
1. A one-way slab spans in the shorter direction, so clear span = 4 m. 2. Clear span + d = 4 + 0.16 = 4.16 m 3. c/c of supports = 4 + 0.23/2 + 0.23/2 = 4.23 m 4. Leff = smaller value = 4.16 m
Explanation
A one-way slab bends along its short span, so we use the 4 m dimension. IS 456 takes the smaller of clear span plus effective depth and the centre-to-centre span. Here 4.16 m is smaller than 4.23 m.
Why the other options are wrong
A (2.23 m) has no basis. C (6.84 m) is not related to either span. D (10.23 m) is the c/c of the long span, which is not used for a one-way slab.
Shortcut
Short clear span + d = 4 + 0.16 = 4.16 m, which is usually smaller than the c/c span when walls are thick.
Common mistake
Using the long span (10 m), or taking c/c distance (4.23 m) without comparing it with clear span + d.
Correct answer: B) 4.16 m