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Composite Constructions

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Composite constructions have contributed significantly to the construction industry and becoming popular with their structural efficiency, technical and constructional advantages writes N Venkatesh, Head QA/QC &ISO Internanl Auditor, BL Kashyap &Sons Ltd.

Composite Constructions are slowly replacing the Structural Steel today used in the used in commercial, Industrial, Residential, School, Cinema and other commercial buildings. Composite Slabs and Beams using Steel Decking is one typical example of Composite Structures which has today gained popularity in construction industry. The following benefits are achievable by adopting Composite Slabs and Beams using Steel Decking in the constructions.

  • Speed and simplicity of constructions due to using of materials like metal decking and simple steel connections. The advantage of decking system is that the bundles of decking can be lifted and positioned through cranes and the individual decks can be lifted by hands. Using this process, over 400sqmt of decking can be installed by one or more teams in a day.
  • Saving in weight due to lighter constructions as composite constructions are relatively stiffer than other conventional flooring systems.
  • Transportation cost of materials like decking material is reduced due to lighter in weight, tighter packing of decks and they can be delivered in pre cut lengths.
  • Provides protection against falling objects from top.
  • Provides space for carrying out all parallel activities.
  • Formwork not needed or they can be bare minimum in large spans.

Composite Slab and Beams using Steel Decking

The typical example to composite construction is Flipkart project undertaken by BLK on outer ring road, Bengaluru which is nearing completion. Here composite slabs are supported on composite columns. The floors of these building are cast with profiled deck sheets with reinforced concrete as infilling material. The profile sheets acted as a sacrificial shuttering during construction and also partly replaced reinforcements in composite form. This was made possible by the provisions of shear studs along the supporting beams. These shear connectors are embossments in the deck sheets in typical pattern unique to deck profile. The embossments provided prevent uplift and develop friction and serve as a mechanical interlock between concrete and steel sheet. These two reactions have taken care of longitudinal shear developed at the interface of concrete and steel preventing slip, thereby enabling the two components to acts as a single unit. To ensure required friction between deck sheet and concrete two key steps were taken in this project. The first step taken was that no oil was applied on the decking before concreting. The second step taken was that no vibrations were allowed during and after construction i.e. till the composite action was achieved in the slab.

The ISMB sections and Decks used in this project for beams and columns were of tested quality. The deck profiles directly from the factory came with connecting accessories like bolts, nuts and welding rods. Minimum welding works were carried on site for fixing the studs and to connect the beams with columns. The columns in this project were cast with ISMB sections using M 80 grade of concrete as the encasing material..

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