Permanent formwork construction method is used to:
Speed construction, especially of downstand beams
Provide high-quality finishes
Promote low tolerances
The units can act solely as permanent formwork, i.e. they may be designed for construction loads only without contributing to the strength of the completed beams.
More efficiently, they can act compositely with the in-situ concrete. Indeed some beams, particularly in seismic areas are designed to act both compositely and non-compositely in the same span.
Non-Composite Permanent Formwork:
Non-composite precast permanent formwork is used to speed the erection process and assure quality finish. This is particularly useful on exposed spandrel beams which require specialized finishes or profiles. Polystyrene void formers can be introduced into rectangular sections to reduce self weight.
The above units can be used in the main elevations supported by trestles and column formwork used in the curved elevation.
Composite Permanent Formwork:
Beam shells perform number of functions:
They are generally designed to support precast floor units and construction loads
To act as formwork for infill in-situ concrete
To act compositely with the in-situ infill to support permanent loads.