19 December 2012
For over 50 years Freyssinet has been involved in the construction of buildings and skyscrapers, optimising their structure through the benefits of prestressed floor technology. With its integrated design, supply and build prestressing solutions, Freyssinet makes its extensive expertise and know-how available to contracting authorities and architects, resulting in the design of ever more functional and durable structures, while at the same time taking account of any operational constraints.
Technical support from the architectural design phase Contemporary architectural trends favour large unbroken floor areas, flexible internal layout and spaces that are easy to modify and move around in, while considerably improving the durability of buildings. All of these requirements can be met through the use of prestressing by post tensioning, which enables the creation of large unobstructed floor areas with a minimum number of columns and reduced floor thicknesses. Freyssinet supports its customers from the design stage in order to optimise structures with a view to reducing costs and construction times while meeting their architectural requirements.
Complete integration of prestressing works into the construction cycle When prestressing operations form part of the construction schedule, the constraints associated with planning and phasing the works constitute a major challenge. Freyssinet’s numerous strengths mean that it is able to guarantee its customers a quality service performed in strict accordance with production cycles: • The Freyssinet prestressing system, with CE marking and compliance certification, is designed for high site productivity; • The Freyssinet-designed installation equipment enables fast, high-quality execution; • Lastly, Freyssinet’s specialist teams meet the training and qualification requirements of standard CWA 14646.
Main benefits Larger slab spans require fewer columns, providing great freedom in terms of layout. • Depending on slab type, elimination of soffits or reduced floor thicknesses. The extra height gained can allow for more levels to be built; • Savings on materials (concrete and steel); • Shallower, less complex foundations; • Reduced delivery times due to fast installation. As well as: • Elimination of deflection under normal conditions of use; • Reduction or elimination of slab contraction joints and floor expansion joints; • Better resistance to cracking caused by shrinkage for improved watertightness and so improved durability. Post tensioned floors result in a 20% reduction in greenhouse gas emissions compared with traditional reinforced concrete designs.
A variety of applications Freyssinet prestressing systems can be used in a variety of applications including industrial slabs and floors, foundation slabs and in-fill structures in buildings. They are a cost-effective, reliable solution for optimising a wide range of structures: • Residential buildings; • Office blocks; • Retail centres; • Underground and above ground car parks; • Hospitals; • Schools; • Business centres; • Industrial buildings; • Sports halls; • Docks, etc.
How does it work? Prestressing involves a number of different steps: 1. Formwork installation 2. Installation of lower mesh and lower beam reinforcements 3. Installation of active anchors on concrete joint formers 3a. Bonded prestressing: installation of sheaths and threading of strands 3b. Unbonded prestressing: installation of greased sheathed strands, which may be prefabricated 4. Creation of passive anchors 5. Creation of tendon profiles using plastic supports 6. Installation of upper reinforcements 7. Inspection of prestressing and reinforcements by a Freyssinet manager 8. Concreting of slabs in the presence of a Freyssinet manager 9. Tensioning to 25% if necessary 10. Tensioning to 100% 11. Elongation monitoring 12. Stripping of slabs 13. Cutting of strands 14. Sealing of anchor recesses 15. Cement grouting of sheaths in the case of bonded prestressing.