What is the minimum grade of concrete for a prestressed tank?

M35 is the minimum grade specified (Clause 4.1).

What is the requirement for stress in the tank wall when full?

No tensile stress is permitted on the liquid-retaining face when the tank is full (Clause 6.1.2).

What is the minimum residual compression required in the tank wall?

A minimum residual compressive stress of 0.7 N/mm² is required when the tank is empty to account for shrinkage and temperature effects (Clause 6.1.3).

Is a sliding base joint permitted?

Yes, the code provides guidance for sliding, hinged, and fixed wall-base joints, with different design considerations for each (Clause 7.2).

IS 11682

: 1985

Code of Practice for Design and Construction of Prestressed Concrete Cylindrical Tanks for Storage of Liquids

CurrentSpecializedCode of PracticeBIMStructural Engineering · Tanks, Silos and Storage Structures

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This standard provides guidelines for the design and construction of prestressed concrete cylindrical tanks for the storage of liquids. It covers material specifications, design principles for ensuring liquid tightness, analysis of stresses, and construction methodologies including prestressing operations and joint detailing.

Provides recommendations for the design and construction of prestressed concrete cylindrical tanks for liquid storage.

Quick Reference Values

Minimum grade of concreteM35

Minimum cement content360 kg/m³

Maximum water-cement ratio0.45

Minimum residual compressive stress (tank empty)0.7 N/mm²

Minimum wall thickness (prestressed)120 mm

Permissible tensile stress in steel (prestressing)Shall not exceed 80% of the characteristic strength

Key Formulas

T = w * H * D / 2 — Ring tension in tank wall due to hydrostatic pressure

Practical Notes

The detailing of the wall-base joint (sliding, hinged, or fixed) is critical and is a common source of leakage. The choice of joint type significantly impacts the design moments and reinforcement.

Accurate calculation of prestress losses (Clause 6.4) is crucial to ensure the tank remains in compression and crack-free throughout its service life. Consider long-term effects like creep and shrinkage carefully.

This code predates modern seismic codes. Designers must supplement it with IS 1893 (latest version) for seismic analysis, properly accounting for impulsive and convective liquid mass actions.