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IS 15099:2002 is the Indian Standard (BIS) for permanent steel formwork for concrete construction - code of practice. This standard provides guidelines for the material, design, and construction of permanent steel formwork systems for concrete structures. It addresses design for the construction stage (supporting wet concrete) and for the final composite section where the formwork contributes to the structure's strength.
Provides guidelines for the design and construction of permanent steel formwork systems for concrete.
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Scaffolding, Formwork and Construction Equipment
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Ensure proper detailing and sealing of joints and overlaps between formwork panels to prevent slurry leakage, which can compromise the concrete quality.
! Strictly adhere to the manufacturer's specified propping scheme during construction, as the formwork's design is based on specific support conditions.
! For composite design, the surface of the steel formwork must have embossments or indentations to ensure adequate mechanical interlock and shear bond with the concrete.
EN 1994-1-1:2004European Committee for Standardization (CEN), Europe
HighCurrent
Eurocode 4: Design of composite steel and concrete structures - Part 1-1: General rules and rules for buildings
Provides general rules for the design of composite structures, including a detailed section on composite slabs with profiled steel sheeting.
ANSI/SDI C-2017Steel Deck Institute (SDI), USA
HighCurrent
Standard for Composite Steel Floor Deck-Slabs
Specifically addresses the design and construction of composite slabs utilizing steel decking, making it a direct counterpart.
AS/NZS 2327:2017Standards Australia / Standards New Zealand, Australia/New Zealand
HighCurrent
Composite structures - Composite steel-concrete construction in buildings
Covers the design of composite steel-concrete members, including composite slabs, similar in approach to Eurocode 4.
BS 5950-4:1994British Standards Institution (BSI), UK
HighWithdrawn
Structural use of steelwork in building - Part 4: Code of practice for design of composite slabs with profiled steel sheeting
A direct predecessor to the Eurocode 4 approach in the UK, it formed the basis for much of the methodology now used.
Key Differences
≠The method for determining the design shear resistance for composite action differs. IS 15099 provides an empirical formula based on specific tests, while Eurocode 4 offers two methods: the empirical 'm-k' method and the more detailed 'Partial Shear Connection' method, which allows for more refined design.
≠Fire design provisions in IS 15099 are less comprehensive, typically providing prescriptive minimum dimensions or referring to other Indian standards. In contrast, EN 1994-1-2 provides detailed calculation models and tabulated data for determining the fire resistance of composite slabs.
≠Material specifications are based on national standards. IS 15099 references Indian steel grades (e.g., from IS 2062), whereas Eurocode 4 references EN standards (e.g., S355) and the SDI standard references ASTM grades (e.g., ASTM A653).
≠While both use a limit state design philosophy, the specific partial safety factors for loads and materials can vary. For example, the partial safety factor for steel decking material strength in Eurocode 4 (γ_A = 1.0) is different from the factor applied in the Indian context (γ_m0 = 1.10 from IS 800).
Key Similarities
≈All standards are based on the fundamental principle of composite action, where the steel deck and hardened concrete act as a single structural unit to resist bending and shear.
≈The design process in all codes involves checking two primary stages: the construction stage (where the steel deck alone supports wet concrete and construction loads) and the composite stage (where the deck and concrete act together under service loads).
≈All codes recognize the dual function of the profiled steel sheeting: acting as permanent formwork during construction and as positive moment (tension) reinforcement in the final composite slab.
≈All standards mandate a mechanism for mechanical interlock and shear transfer between the steel deck and the concrete, typically achieved through embossments, indentations, or the profile's geometry.
≈Serviceability limit state checks for deflection are a key requirement in all standards for both the construction and final composite stages to ensure structural performance and integrity.
Parameter Comparison
Parameter
IS Value
International
Source
Deflection Limit (Construction Stage)
Lesser of Span/180 or 20 mm (under weight of steel and wet concrete)
Lesser of Span/180 or 20 mm is a common practice; some specifications use Span/240.
EN 1994-1-1 (Common Practice)
Minimum Total Slab Thickness
90 mm
80 mm (though often 90-100 mm in practice)
EN 1994-1-1
Minimum Concrete Cover over Decking Ribs
50 mm
50 mm
EN 1994-1-1
Minimum Imposed Load (Construction)
Not less than 1.5 kN/m² (uniformly distributed)
Minimum 0.75 kN/m²; typically 1.5 to 2.0 kN/m² is used for design (Qca).
What is the minimum thickness for permanent steel formwork sheets?+
The base metal thickness shall not be less than 0.5 mm, as per Clause 4.1.1.
What is the maximum deflection allowed for the formwork during concreting?+
For the formwork acting alone under its own weight plus the weight of wet concrete, the deflection is limited to the lesser of Span/180 or 20 mm (Clause 5.2.2).
Can the steel formwork be considered part of the final structural system?+
Yes, it can be designed to act compositely with the hardened concrete slab to resist superimposed loads, provided the conditions in Clause 5.3 are met.
What standard is followed for corrosion protection of the steel sheets?+
The steel sheets should be galvanized as per IS 277, with a minimum zinc coating mass of 275 g/m² (Clause 4.1.2).