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IS 3935:1966 is the Indian Standard (BIS) for composite construction. This code covers the design and construction of composite concrete structures made up of prefabricated structural units (reinforced or prestressed) and cast-in-situ concrete. It focuses on ensuring monolithic action between the distinct concrete pours.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Surface preparation is vital: the precast concrete surface must be suitably roughened, cleaned of laitance, and wetted before placing the cast-in-situ concrete to ensure proper shear transfer.
! Unpropped construction requires the precast unit to be designed to independently carry its self-weight, the wet weight of the in-situ concrete, and all construction live loads.
! Always account for differential shrinkage and creep in the design, as the precast member is typically much older than the cast-in-situ topping when monolithic action begins.
EN 1994-1-1:2004European Committee for Standardization (CEN), Europe
MediumCurrent
Eurocode 4: Design of composite steel and concrete structures - Part 1-1: General rules and rules for buildings
Both cover design of composite beams and slabs, but Eurocode 4 is far more comprehensive and uses a modern design philosophy.
ANSI/AISC 360-22American Institute of Steel Construction (AISC), USA
MediumCurrent
Specification for Structural Steel Buildings
Chapter I of AISC 360 covers composite construction, addressing the same fundamental elements as IS 3935.
BS 5950-3.1:1990British Standards Institution (BSI), UK
HighWithdrawn
Structural use of steelwork in building - Part 3.1: Design in composite construction - Code of practice for design of simple and continuous composite beams
Represents the direct evolution from the principles in IS 3935, albeit using a Limit State Design approach.
BS 449:1959British Standards Institution (BSI), UK
HighWithdrawn
Specification for the use of structural steel in building
IS 3935 is heavily based on the Allowable Stress Design principles and practices of this era of British standards.
Key Differences
≠IS 3935 is based on the Working Stress Method (WSM), an outdated elastic design philosophy. Modern codes like Eurocode 4 and AISC 360 use the Limit State Design (LSD) or Load and Resistance Factor Design (LRFD) method, which considers ultimate and serviceability limit states with partial safety factors.
≠The Indian standard IS 3935:1966 is officially withdrawn. Composite construction in India is now primarily governed by IS 11384 and Chapter 15 of the more recent steel code, IS 800:2007.
≠Shear connector design in IS 3935 is based on simple allowable loads for connectors. Modern codes employ detailed calculations for connector resistance and ductility, allowing for the concept of 'partial shear connection' which is not addressed in the old Indian standard.
≠IS 3935 uses a simplified modular ratio 'm' (often tripled to 3m) to account for long-term effects like creep and shrinkage. Modern standards use more sophisticated methods involving creep coefficients and shrinkage strain calculations for more accurate deflection and stress analysis.
Key Similarities
≈All standards are founded on the same basic principle: combining a steel beam with a concrete slab to create a structurally efficient composite T-beam, utilizing the concrete in compression and the steel in tension.
≈Both IS 3935 and its international counterparts mandate the use of mechanical shear connectors (like studs, channels, or bars) to transfer horizontal shear between the steel and concrete components, thereby ensuring composite action.
≈The concept of an 'effective flange width' is common to all standards. They all recognize that only a limited width of the concrete slab contributes effectively to the strength and stiffness of the composite beam and provide rules to calculate it.
≈All codes consider the construction sequence, analyzing the steel beam for stresses when it supports the wet concrete and formwork (non-composite stage) and then analyzing the composite section for superimposed loads.
Parameter Comparison
Parameter
IS Value
International
Source
Design Philosophy
Working Stress Method (WSM)
Limit State Design (LSD) / LRFD
EN 1994-1-1 / AISC 360-22
Material Factor for Concrete (Compression)
Factor of Safety of approx. 3.0 on characteristic strength (embedded in allowable stress)
Partial safety factor γ_c = 1.5
EN 1994-1-1
Material Factor for Steel (Yielding)
Factor of Safety of approx. 1.67 on yield stress (embedded in allowable stress)
Partial safety factor γ_M0 = 1.0
EN 1994-1-1
Effective Width of Slab (Internal Beam, simplified)
Lesser of: Span/3, or Centre-to-centre beam spacing
Centre-to-centre beam spacing or L0/4, where L0 is the distance between points of zero moment.
EN 1994-1-1
Treatment of Creep & Shrinkage
Use of a long-term modular ratio (e.g., 3m, where m = Es/Ec)
Use of a creep coefficient (φ) to determine an effective modulus for concrete: Ec,eff = Ecm / (1+φ)
EN 1994-1-1
Shear Connector Design
Based on tabulated allowable shear loads for specific connector types.
Calculated design resistance (P_Rd) based on material strengths, ductility, and failure modes (connector or concrete).
EN 1994-1-1
Consideration of Partial Interaction
Not considered; assumes full shear connection.
Permitted and explicitly calculated; allows for an economical design with fewer shear connectors.
AISC 360-22 / EN 1994-1-1
⚠ Verify details from original standards before use
Key Values3
Quick Reference Values
Minimum bearing on masonry supports100 mm
Minimum bearing on concrete or steel supports75 mm
Typical minimum thickness of cast-in-situ structural topping40 mm
Key Formulas
v = V / (b * d) — Horizontal shear stress at the interface between precast and cast-in-situ concrete
Are shear connectors strictly required between the precast and cast-in-situ concrete?+
Not always. For low shear forces, a properly roughened interface may provide sufficient bond. For higher shear, projecting steel ties or stirrups crossing the interface are required.
When is propping required for precast units?+
Propping is required during the pouring and curing of the in-situ topping unless the precast units are explicitly designed for 'unpropped' construction to handle the wet concrete load.
How does this code relate to IS 456?+
This code acts as a supplementary guide specifically for the composite action interface and staging; general reinforced concrete design principles of the members must still comply with IS 456.