A new ultra long-spanning, combined steel formwork and reinforcement hybrid decking system using cold-formed components

A new ultra long-spanning, combined steel formwork and reinforcement system designed to span up to 6 or 7 metres (20.7 or 23 feet) without propping has been under development for nearly a decade in Australia. The steel decking system includes a number of innovative features that make it adaptable to almost any type of building construction ranging from conventional, shallow one-way composite slabs in steel-frame buildings to deep two-way post-tensioned slabs in concrete-frame buildings. The hybrid system comprises a number of distinctly different cold-formed steel components, which have efficient shapes and utilize different thicknesses, steel grades and coatings. The overall height of the main decking panel can vary from 90 to 260 mm (3.54 to 10.24 in) with an additional three intermediate sizes, despite the components being made from the same roll- forming equipment. The panel has a closed cellular section and is pre-cambered to limit the final deflection under wet-concrete conditions. These panels can be interconnected for maximum spanning capability, or else different types of in fill panels can be fitted between them to form composite slabs with a variety of cross-sectional shapes and features. Slabs of minimum overall depth or minimum weight can be constructed using the system. The cellular section can form a void in the concrete, or it can have holes pre-punched in its webs allowing it to be filled with concrete either partially or completely along its length. Prestressing cables and reinforcing bars can be fitted longitudinally and if need be transversely in the slab, even in the soffit region. Comprehensive sets of structural tests, some quite innovative, are currently being performed to thoroughly investigate the behaviour of the system for both the formwork and composite states. In particular, this involves developing a complete understanding of the complex behaviour of the main decking panel and its different cold-formed components under a variety of loading conditions that induce vertical and longitudinal shear, longitudinal and transverse bending, and torsion. The behaviour of the mechanical connection between the elements is being closely investigated experimentally, allowing the moment capacity of potentially critical cross-sections with partial shear connection to be accurately predicted and the spacing between connections optimised.