Mobile prestressing bed for the production of prestressed ceiling elements on existing production tables
The production of prefabricated floor slabs usually takes place in a circulation system or on stationary production tables. As these components are untensioned, the performance of the floor elements remains limited. However, with a prestressed reinforcement, further application possibilities open up. The advantages such as slender, resolved cross-sections and the associated CO2 reduction are optimally achieved with a prestressed reinforcement.
Traditionally, the prestressing in the prestressing bed is based on a more or less long prestressing line with large abutment constructions on both sides. Such devices are usually designed for wide-span downstand beams or at best for double tee slabs. Due to the two different processes, the use of a pretensioned prestressing on tables for floor slab production is currently ruled out.
Since prestressed, prefabricated floor slabs will play a greater role in the future due to their properties, the aim is to expand existing tables for the production of floor elements to include the option of a prestressing bed. This technique is made possible with the help of a mobile prestressing bed.
In contrast to the traditional prestressing bed with prestressing line and abutment, the prestressing forces are short-circuited via additional load-bearing beams when using a mobile prestressing bed. The prestressing yokes on both sides are supported on stable reinforced concrete beams. The prestressing force introduced at the prestressing yokes is released via the longitudinal pressure beams and is in equilibrium with the prestressed strands in the prestressing bed.
The existing production tables are lined up and included in the prestressing bed. On the two long sides of the tables, prefabricated reinforced concrete beams are placed on top and underneath the table. The beams are additionally attached to the existing tables. The prestressing yokes at the beginning and at the end of the set-up production tables transfer the forces created by the pre-tensioning into the pressure beams.
The cross yokes for anchoring the tensioning strands are usually designed in such a way that one to two levels of prestressing wires can be installed. This allows not only panels to be centrally prestressed, but also slender beams with a low height.
Since the existing production tables usually have large widths, several different components can be produced side by side at the same time to achieve maximum occupancy. The range of application includes thin semi-precast slabs, slabs with sandwich cross-section, ribbed slabs and slender downstand beams.
The presentation reports on the practical experience with a mobile prestressing bed in various precast plants. The structure and function of the mobile prestressing bed are shown. The production of prestressed floor slabs of all types and of slender downstand beams is reported. The benefits of prefabricated and prestressed floor slabs are also reported.