IS 3370:2009 Part 2 is the Indian Standard (BIS) for concrete structures for storage of liquids - code of practice - reinforced concrete structures. Provides design requirements for reinforced concrete structures storing liquids. The 2009 revision introduced the Limit State Method for design while continuing to permit the Working Stress Method, heavily emphasizing crack width control to ensure watertightness and durability.
Specifies requirements for design and construction of reinforced concrete structures for the storage of liquids.
IS 3370 Part 2 (2009) is the Code of Practice for Concrete Structures for Storage of Liquids — Part 2: Reinforced Concrete Structures. Used for designing water tanks, sewage tanks, treatment plant structures, fuel storage, and other liquid-retaining structures.
Use IS 3370 Part 2 when designing: - Water tanks (overhead, ground, underground) - Sewage treatment plant tanks - Industrial liquid storage - Fire-water tanks - Treatment plant primary + secondary structures
Key requirements: - Crack width limited to 0.1 mm for water-retaining structures - Stricter cover (≥ 40 mm) than standard concrete - M30 minimum concrete grade for severe exposure - Reinforcement detailed for crack control
Design philosophy: - Crack-width limited approach (vs strength-only) - Hoop tension in walls - Bending + axial combined check - Watertightness verified by hydrostatic test - Service life: 25-50 years (typical) up to 75+ with quality
Concrete grade: - M30 minimum for liquid contact - M35-M40 for sewage / chemical exposure - M40+ for high-pressure / coastal
Reinforcement: - Fe 500 typical - Cover ≥ 40 mm (face in liquid contact) - Smaller bar diameters preferred (better crack control) - Distribution + main reinforcement together
Walls: - Cylindrical (circular tanks) — hoop tension dominant - Rectangular — bending + tension - Conical (clarifiers) — combined - Thickness: 150-400 mm typical depending on size + depth
Crack width: - Service: ≤ 0.1 mm - Limit: 0.2 mm in non-critical zones
Concrete cover: - Liquid face: ≥ 40 mm - Air face: ≥ 30 mm - Severe (sewage): ≥ 50 mm
Reinforcement detail: - Distribution rebar minimum 0.24 % of cross-section - Main bar: per stress analysis - Spacing: ≤ 300 mm or ≤ 1.5 × wall thickness - Bond length per IS 456
Construction tolerances: - Wall thickness: ± 5-10 mm - Cover: ± 10 mm - Surface evenness: 3 mm under 3-m straight-edge
Quality control: - Cube test per IS 1199 Part 1:1986 - Cover meter verification - Cores for in-situ verification - Hydrostatic test pre-commissioning (24 hours water retention)
Acceptance: - Visual: no visible cracks under hydrostatic test - Leak rate: typically ≤ 5 mm/24hr (per spec) - Surface dry on outer face - Long-term: 5-7 year inspection cycle
1. Inadequate cover → corrosion + spalling within 10 years. 2. Crack width > 0.1 mm → leakage; failure. 3. Concrete grade < M30 → durability issues. 4. Hydrostatic test skipped → leakage discovered in service. 5. No expansion joints in long structures → uncontrolled cracking. 6. Wrong cement for sulphate environment → use sulphate-resisting. 7. No proper waterproofing → leakage despite design. 8. No periodic inspection → silent deterioration.
1. Design per IS 3370 Part 2 + IS 456 + IS 1893. 2. Detailed drawings + BOQ. 3. Construction: foundations → walls → roof → finishes. 4. Hydrostatic test (24-hour water retention). 5. Commissioning + handover. 6. Annual visual + 5-year detailed inspection. 7. Service life 50+ years with maintenance.
IS 3370 Part 2 is the design reference for India's liquid-retaining concrete structures — applied on every water tank, sewage tank + treatment plant structure.