Code of practice for composite construction
1966 Edition

According to Clause 6.4.2 of IS 3935, shear connectors recommended include: Flexible types such as studs and channels welded onto prefabricated elements, which primarily resist shear through bending; Bond or anchorage connectors like mild steel bars formed into vertical or inclined loops, stirrups, or bent bars, which resist shear via bond and anchorage; and other mechanical devices designed to prevent horizontal shear and vertical separation. Connectors must be made of weldable steel conforming to applicable IS standards, with welding strength equal to or exceeding the connector’s shear resistance. Stud connectors require specialized fusion welding and should maintain a minimum 15 mm spacing between adjacent stud heads to ensure proper weld quality.

IS 3935 defers to existing Indian Standards for permissible stresses within composite members: Reinforced concrete members follow IS 456:1964 guidelines; prestressed concrete members adhere to IS 1343:1960 provisions; and structural steel components comply with IS 800:1962 requirements. The standard integrates these codes to ensure safe and reliable design by adopting established allowable stress values rather than introducing new limits.

To achieve effective bond strength, IS 3935 specifies ensuring a roughened interface surface to promote mechanical interlocking (Clause 7.2). The longitudinal shear stress along the interface between shear connectors must not exceed 2.5 times the permissible shear stress of concrete (Clause 2.5b). Additionally, the projected area along the slope between connectors should be at least three times the connector’s face area (Clause 2.5c) to facilitate adequate load transfer. Proper shear connector design per Clause 6.5 is essential to prevent slip and maintain composite action under ultimate loads.

Deflection calculations under IS 3935 vary based on loading and construction conditions: For beams supported during construction, dead load deflections are computed using the transformed composite section’s moment of inertia and half the concrete’s modulus of elasticity (Clause 5.8.2.1). Live load deflections use the same moment of inertia but apply the full modulus of elasticity (Clause 5.8.1). For beams without shoring, dead load deflections initially consider only the prefabricated beam’s inertia, switching to the composite section method once the slab attains 75% of its 28-day strength (Clause 5.8.2.2). Deflection limits are span-dependent, typically span/600 for total load and span/800 for live load in simply supported beams, ensuring serviceability.

Shear connectors must be fabricated from weldable steel, with end welding to the structural member to ensure adequate load transfer (Clause 6.4.1.1). The weld strength must be at least equal to the connector’s shear resistance. Welding should conform to relevant Indian Standards such as IS 816. Stud connectors require specialized fusion welding techniques, and a minimum spacing of 15 mm between adjacent stud heads must be maintained to avoid welding defects. These precautions guarantee the connectors’ structural reliability and effective composite action.