IS 3370:2021 Part 1 is the Indian Standard (BIS) for concrete structures for storage of liquids - part 1: general requirements. This part of the code specifies the general requirements for the design and construction of plain, reinforced, and prestressed concrete structures intended for the storage of liquids, emphasizing durability, crack control, and water-tightness.
Lays down general requirements for the design and construction of concrete structures for the storage of liquids.
Concrete grade, w/c, cover, crack-width, permissible tensile/compressive stresses and joint spacing for water-retaining concrete structures.
| Reference | Value | Clause |
|---|---|---|
| Min concrete grade — liquid-retaining structures | M30 | Cl. 7.1 |
| Max water-cement ratio | 0.45 | Cl. 7.1 |
| Min cement content | 320 kg/m³ | Cl. 7.1 |
| Min nominal cover — face in contact with liquid | 40 mm | Cl. 8.1 |
| Min nominal cover — other faces | Per IS 456 exposure category | Cl. 8.1 |
| Crack width limit — severe exposure (liquid face) | 0.2 mm | Cl. 9.2 |
| Crack width limit — moderate exposure | 0.3 mm | Cl. 9.2 |
| Permissible tensile stress — Fe415 (direct, σst) | 150 N/mm² | Cl. 9.3 (Table 4) |
| Permissible tensile stress — Fe415 (bending, σst) | 190 N/mm² | Cl. 9.3 (Table 4) |
| Permissible tensile stress — Fe500 (direct) | 180 N/mm² | Cl. 9.3 (Table 4) |
| Permissible tensile stress — mild steel (Fe250) | 115 N/mm² (direct), 125 N/mm² (bending) | Cl. 9.3 (Table 4) |
| Min steel — each face/direction (mass-control) | 0.24 % (Fe415/500) × gross area | Cl. 8.2.1 |
| Min steel — walls 100–500 mm (each face) | 0.20 – 0.30 % (interpolated by thickness) | Cl. 8.2.1 (Table 3) |
| Joint spacing — movement joints (typical) | ≤ 7.5 m (full movement); ≤ 15 m partial | Cl. 10.2 |
| Joint spacing — construction joints | Designed; typical 5–7 m | Cl. 10.3 |
| Permissible compressive stress — concrete (M30, direct) | 8 N/mm² | Cl. 9.4 (Table 5) |
| Permissible compressive stress — concrete (M30, bending) | 10 N/mm² | Cl. 9.4 (Table 5) |
| Hydrostatic test — duration after curing | 7 days minimum | Cl. 11 |
| Permissible drop in water level (test) | ≤ 1/500 of average depth (or 40 mm) | Cl. 11 |
| Design method permitted | Working stress (Cl. 9) or limit state (refer Part 2) | Cl. 6 |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 3370 Part 1:2021 is the current general-requirements part of the code for concrete structures for the storage of liquids — water-retaining structures: overhead/underground tanks, clear-water reservoirs, sumps, ETP/STP tanks, swimming pools. Part 1 sets the overarching durability/serviceability philosophy; Parts 2 (RC) and 3 (prestressed) give the design provisions, Part 4 the design tables.
It is read with:
A water-retaining structure must be crack-controlled and impermeable, not just strong — leakage and durability govern, so IS 3370 overlays tighter requirements on ordinary IS 456 design:
The whole point: an IS-456-adequate tank can still leak; IS 3370 exists to make it *not leak*.
Element: an RC water-tank wall (cantilever from base), liquid pressure governing.
Step 1 — actions: triangular hydrostatic pressure → design moment & direct tension in the wall; use the IS 3370 Part 4 coefficients for the wall edge conditions / aspect ratio.
Step 2 — strength (IS 456): size section & flexural steel for the moment (limit state) — usually *not* the governing check.
Step 3 — crack width (the governing check, IS 3370 Part 2): compute the design surface crack width under service load + restrained thermal/shrinkage; provide enough, well-distributed, closely-spaced bars so crack width ≤ the IS 3370 limit (≈0.2 mm liquid face). This typically dictates more, smaller-diameter bars than strength alone.
Step 4 — minimum reinforcement: surface-zone steel per IS 3370 to control early-thermal/shrinkage cracking (often governs thin walls/slabs).
Step 5 — durability & test: M30-class low-permeability concrete, generous cover, extended curing; waterstops at joints; fill-and-leak test the finished tank to the IS 3370 acceptance limit before commissioning.
1. Designing the tank to IS 456 strength only. It will pass strength and still leak — the *crack-width* and *minimum-reinforcement* checks of IS 3370 are what stop leakage and are usually the governing design.
2. Under-reinforcing for thermal/shrinkage cracking. Early-age thermal & drying shrinkage cracks are the commonest tank leak path; the IS 3370 minimum surface steel is not optional.
3. Ordinary concrete & short curing. Permeability — not strength — governs durability here; low w/c, adequate cement, full compaction and *extended* curing are mandatory, not nice-to-have.
4. Poor joint/waterstop detailing. Tanks leak at construction/expansion joints first; waterstops and joint sequencing must be designed and supervised.
5. Skipping the watertightness test. The fill-and-measure leak test is the acceptance proof — commissioning without it ships an unverified tank.
IS 3370 Part 1:2021 is the current revision (modernised crack-control approach, aligned in philosophy with EN 1992-3) and is the controlling code for every water-retaining structure — and water tanks/STP-ETP tanks are on almost every infrastructure and building project. The defining mental model: IS 3370 is a serviceability (crack-width + impermeability) code sitting on top of IS 456 strength — leakage, not collapse, is the failure mode it prevents.
The practitioner essentials: design walls/slabs for crack width and minimum thermal/shrinkage steel as the governing checks, specify low-permeability concrete with extended curing, detail waterstops and joint sequencing, and always do the fill-and-leak acceptance test. Tank leakage in service is almost never a strength failure — it is a crack-control, concrete-permeability or joint-detailing failure, which is precisely the set of things IS 3370 (not IS 456 alone) governs.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Minimum Concrete Grade | M30 | 28 MPa (~M28) specified compressive strength (f'c) | ACI 350-20 |
| Maximum Water-Cement Ratio (Severe Exposure) | 0.45 | 0.45 | ACI 350-20 |
| Minimum Nominal Cover (Liquid Face, Severe Exposure) | 45 mm | 50 mm (2 in.) | ACI 350-20 |
| Design Crack Width Limit (Liquid Face) | Not explicitly defined; controlled indirectly by limiting steel stress to 130 MPa (for HYSD bars). | 0.25 mm (0.010 in.) | ACI 350-20 |
| Load Factor for Fluid Pressure (ULS) | 1.5 | 1.4 | ACI 350-20 |
| Watertightness Test Duration | 7 days | Generally 24 hours (after a stabilization period), but can vary. | ACI 350.1-10 |
| Minimum Cement Content (Severe Exposure, 20mm aggregate) | 340 kg/m³ | 320 kg/m³ (For comparable XD1 exposure class) | EN 1992-1-1:2004 |