The shuttering (props) of a hall measuring 4 m × 5 m can be removed after:
Correct Answer: B. 7 days
📚 Detailed Explanation: Hall 4 m × 5 m — Prop Removal After 7 Days
Why B (7 days) is correct: For two-way slabs, the governing (shorter) span determines the structural behaviour. The shorter span here is 4 m, which falls in the “spanning up to 4.5 m” category in IS 456:2000. Therefore props can be removed after 7 days.
How to Identify the Governing Span
| Hall Dimension | Shorter Span | IS 456 Category | Min. Period |
|---|---|---|---|
| 4 m × 5 m | 4 m (< 4.5 m) | Props to slabs: up to 4.5 m | 7 days |
| 5 m × 6 m (example) | 5 m (> 4.5 m) | Props to slabs: over 4.5 m | 14 days |
IS 456:2000 Prop Removal for Slabs
| S.No. | Type of Formwork | OPC (Minimum Period) | RHC (Minimum Period) |
|---|---|---|---|
| 1 | Vertical formwork to columns, walls, beams | 16–24 hours | 12 hours |
| 2 | Soffit formwork to slabs (props refixed immediately) | 3 days | 2 days |
| 3 | Soffit formwork to beams (props refixed immediately) | 7 days | 5 days |
| 4a | Props to slabs: spanning up to 4.5 m | 7 days | 5 days |
| 4b | Props to slabs: spanning over 4.5 m | 14 days | 10 days |
| 5a | Props to beams and arches: spanning up to 6 m | 14 days | 10 days |
| 5b | Props to beams and arches: spanning over 6 m | 21 days | 14 days |
- For a 4 m × 5 m slab, shorter span = 4 m < 4.5 m → props removable after 7 days.
- Had the shorter span been just 0.5 m more (4.5–5 m), the minimum would jump to 14 days.
- The 5 m (longer) span does NOT govern — shorter span controls for two-way slabs.