Maximum permissible deflections for RCC beams and slabs to prevent damage to finishes, partitions, and visual concern. The total deflection (instantaneous + long-term creep + shrinkage) must not exceed these limits. Stricter limit applies if the member supports brittle finishes or partitions.
IS 456 Cl 23.2(a) — Total Deflection Limits
| Case | Limit | Applies To | Note |
|---|
| Final deflection (all sources) | Span / 250 | Floors, roofs, all members | Sum of dead load + live load + creep + shrinkage |
| After construction of partitions | Span / 350 | Members supporting brittle partitions | Or 20 mm, whichever is less |
| After construction of partitions | 20 mm | Members supporting brittle partitions | Absolute maximum |
Practical Limits for Different Members
| Case | Limit | Applies To | Note |
|---|
| Roof slab (no ceiling) | L / 250 | Industrial roofs, sheds | Functional limit only |
| Floor slab (with finishes) | L / 250 or L / 350 | General floors | L/350 if marble/granite/tile |
| Floor with brittle partitions | L / 350 | Brick walls, glass partitions | Critical for brick partition cracks |
| Floor with flexible partitions | L / 250 | Plasterboard, gypsum walls | — |
| Cantilever slab/beam | L / 125 | Cantilever tip deflection | L = projection length, more lenient |
| Bridge deck | L / 800 (live load) | IRC bridges | IRC:21 — much stricter |
| Crane gantry | L / 600 (live load) | Industrial crane runways | IS 800 Table 6 |
Steel Beam Deflection Limits (IS 800 Table 6)
| Case | Limit | Applies To | Note |
|---|
| Industrial roof — no plaster ceiling | L / 180 | Live load only | Most lenient |
| Industrial floor | L / 240 | Live load | — |
| Floor — with plaster ceiling | L / 360 | Live load | Crack-sensitive ceiling |
| Floor — supporting brittle finishes | L / 360 | Total load | Same as IS 456 |
| Crane runway (manual) | L / 500 | Live load | — |
| Crane runway (electric > 50 t) | L / 1000 | Live load | Stricter for heavy cranes |
| Lateral deflection (storey) | h / 300 | Wind/seismic | h = storey height |
Components of Total Deflection
| Case | Limit | Applies To | Note |
|---|
| Instantaneous (elastic) | 5wL⁴/384EI (SS) | DL + LL | Compute with effective Ieff (Annex C-2) |
| Creep deflection | 1.6 × instantaneous (DL) | Permanent loads | Long-term factor 1.6 for normal weather (28-day load) |
| Shrinkage deflection | k₃ × Ψcs × L²/8 | All members | Ψcs = shrinkage curvature, IS 456 Annex C-3 |
| Temperature deflection | Calc separately | Roof slabs, exposed members | Add for unrestrained members |
Notes
• L = effective span (centre-to-centre or face-to-face + d, whichever less) for beams/slabs
• L = projection length for cantilevers (NOT the slab span)
• Long-term deflection in normal exposure ≈ 2.5 × instantaneous (creep + shrinkage)
• If L/d ratio satisfies Cl 23.2.1, you do NOT need to compute deflection — automatic compliance
• For aesthetic concerns (sagging visible to occupants), camber is recommended for L/d > 25
• Tile cracking is the most common deflection complaint — use L/350 if floor has marble or large tiles
• Steel beams are more flexible per kg than concrete — pay extra attention to deflection in pre-engineered buildings
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