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IS 804:1989 is the Indian Standard (BIS) for design of steel structures for overhead water tanks. This standard covers the design, fabrication, and erection requirements for steel overhead water tanks and their supporting structures (staging). It provides structural guidelines to ensure stability against lateral loads (wind and seismic) and dictates requirements for standard steel tank panels, joints, and watertightness.
Lays down requirements for the design of steel structures supporting overhead water tanks.
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Tanks, Silos and Storage Structures
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! When designing the staging (supporting structure), wind and seismic loads should be evaluated carefully, but as per IS codes, their maximum conditions are generally not assumed to act simultaneously.
! Corrosion is a major failure mode for steel water tanks. Ensure robust protective coatings (epoxy paints, galvanizing) are specified and maintained.
! For rectangular pressed steel tanks, standard pre-fabricated panels (usually 1.22m x 1.22m) are bolted together with appropriate jointing compounds to prevent leakage.
steelstructural steelpressed steel
International Equivalents
Similar International Standards
BS EN 1993-4-2:2007CEN - European Committee for Standardization, Europe
HighCurrent
Eurocode 3: Design of steel structures - Part 4-2: Tanks
Directly addresses the structural design of steel tanks, including elevated tanks and their supporting structures.
AWWA D100-21American Water Works Association, USA
HighCurrent
Welded Carbon Steel Tanks for Water Storage
Comprehensive standard for design, fabrication, and erection of welded steel water storage tanks.
API 650, 13th EditionAmerican Petroleum Institute, USA
MediumCurrent
Welded Tanks for Oil Storage
Covers design of large, ground-supported, welded, low-pressure storage tanks; many structural principles are transferable.
Key Differences
≠Design Philosophy: IS 804:1989 is based on the Allowable/Working Stress Method (WSM), whereas modern international standards like EN 1993 and AWWA D100 are based on Limit State Design (LSD) or Load and Resistance Factor Design (LRFD).
≠Load Combinations: IS 804 uses unfactored service loads with permissible stresses. International standards use multiple factored load combinations to check ultimate limit states and serviceability limit states separately.
≠Seismic Analysis: IS 804 references IS 1893, whose older versions used a simplified equivalent static method. Modern codes like EN 1993-4-2 and AWWA D100 mandate a more sophisticated two-mass (impulsive and convective) dynamic analysis for seismic design.
≠Material Specifications: IS 804 specifies Indian steel grades (e.g., IS 2062). International codes reference their respective regional standards like ASTM (for AWWA) and EN (for Eurocode), which may have different properties and designations.
Key Similarities
≈Stability Checks: All standards mandate checking the structure's stability against overturning, sliding, and uplift from wind or seismic loads, often requiring a minimum factor of safety (e.g., 1.5).
≈Consideration of Loads: The fundamental loads considered for design are consistent, including dead load, live load (hydrostatic pressure from water), wind load, and seismic load.
≈Corrosion Allowance: The principle of providing a corrosion allowance or a robust protective coating system for durability is a common requirement in all standards for steel tanks.
≈Minimum Plate Thickness: All codes specify a minimum thickness for the tank shell, bottom, and roof plates to ensure structural stability, prevent buckling, and provide rigidity during construction and service.
Parameter Comparison
Parameter
IS Value
International
Source
Design Philosophy
Working Stress Method (WSM)
Limit State Design (LSD)
EN 1993-4-2:2007
Permissible Bending Stress (in supporting structure)
0.66 * Fy (Yield Stress)
Design Bending Moment (M_Ed) ≤ Design Resistance (M_pl,Rd). Not a direct stress comparison.
EN 1993-1-1
Minimum thickness for tank bottom plates
6 mm
6 mm (1/4 in) for bottoms resting on foundations
AWWA D100-21
Factor of Safety against Overturning (Wind)
≥ 1.5
Restoring Dead Load Moment ≥ 1.5 x Overturning Moment
What code dictates the allowable stresses for the steel staging structure?+
IS 800 is referenced for the structural design and allowable stresses of the steel staging.
How is lateral loading calculated for overhead tanks?+
Wind loads are derived from IS 875 (Part 3) and seismic forces from IS 1893 (Part 4), considering the structure as an elevated mass.
What is the standard procedure for testing the watertightness of the tank?+
The tank is filled completely with water and observed for at least 24 hours to ensure there is no leakage or sweating at the joints.
What is the minimum thickness for the steel plates used in the tank body?+
Typically 5 mm, but this increases depending on the depth of the water (hydrostatic pressure) and whether the plate is used for the bottom, sides, or roof.