Prestress Concrete Technology
By prestressing reinforced-concrete elements, the optimum use of the basic structural materials is achieved. Compared to conventional precast elements where the Prestress Concrete Technology was not applied, this results in a potential savings of 10-20% in construction materials.
The basic principle of prestressing reinforced-concrete precast elements is to apply prestress on an elements, which leads to better mechanical properties. Thanks to the optimum use of structural materials in the prestressed precast element, it is thus possible to significantly reduce its structural height or the number of elements in the structure to be built.
Prestressing technology is used, for example, for hollow-core slabs, girders (I, T, TT-shaped), trusses, columns and wall and slab elements.
When producing reinforced-concrete precast elements from prestress concrete, high-strength prestressing steel cables, which also reinforce the element, are inserted into the moulds for concrete. In exceptional cases, non-metallic carbon fibre reinforcement is used.
The prestressing technology is placed at the start and end points of moulds for concrete for the production of precast elements.
The steel cables are tensioned by means of a special device (stressing jacks), which is controlled by pressure oil from the associated hydraulic unit.
High-strength certified anchors, which grip the steel cables and clamp onto the steel crossbars, are used for locking the stressed cables. The steel cables pass through steel crossbars.
All tensile elements created by the stressed cables are transferred through the anchors and crossbars to steel girders, called bracers.
The bracers are built into the foundation of the surrounding structures of precast production plants. A pair of bracers is always used – at the start and end of the prestressing line (in front of and behind the mould for concrete).
The bracer needs to be able to transfer all loads from the prestressed cables. Depending on the type of reinforced-concrete element being produced, tensile elements of up to 8000 kN are commonly…
- tensioning line length
- not limited in production (normally up to 100 m)
- resulting axial force in the cables
- normally 8000 kN (35 cables × 225 kN)
- element height
- approximately 100–2000 mm
- element width
- not limited
- upper prestressing