Multifunctional concrete ceiling
Multifunctional concrete ceilings are a further variant of the building ceilings made of concrete, which, based on the design theory with the functional integration, pursue the goal of covering as many technical functions as possible with as few components as possible. In the case of the concrete product to be described, the multifunctional use consists in not only using the material concrete as a load-bearing element, but also using its properties as an active and passive energy store. The functional integration then consists of installing all of the building services lines within the ceiling cross-section.
Building ceilings and their static function
Building ceilings are created as a load-bearing element in the form of beam ceilings or flat ceilings and then span freely from support to support. Columns and walls act as supporting bearings. The separation of the load-bearing construction and the addition of the building technology components below and above the load-bearing cross-section leads to a sequential approach both in planning and in execution.
The load-bearing elements of the ceiling construction are specified, planned and implemented. Then the elements of the building services are installed. They are arranged largely below or above the load-bearing ceiling construction. In order to conceal the suspended cables of the building services, thin suspended ceilings are placed below the load-bearing ceiling structure. Cables are also positioned in the raised cavity or double floor .
This creates a ceiling structure that is larger than the load-bearing raw ceiling. The higher floor heights associated with this lead to a building volume that can only be used to a limited extent with the same room heights . This additional volume must also be managed.
New requirements as a result of energy saving
With the integration of the component activation within the full concrete cross-section, the first uses for multifunctional use were considered. The additional use of the concrete cross-section as a passive and active energy store enables energy savings to be made while the building is in operation. The large free areas of the ceiling and wall allow energy to be distributed at a low temperature level. In addition, the adapted surface temperature creates a high level of thermal comfort. The energy transfer via radiation instead of convection creates a pleasant feel-good climate with the lowest air speeds and without a large amount of dust being raised. Pleasantly tempered surfaces of the rooms allow a reduction in the room air temperature and lead to a further reduction in energy consumption .
The inevitable omission of the suspended ceiling during component activation calls for new solutions for the arrangement of the other building services lines. All that remains is the load-bearing cross-section itself. In the case of the full cross-sections of the flat ceilings , however, it should be noted that the inserted pipes significantly reduce the shear force resistance. For this reason, the lines within the full cross-section must be precisely planned and accordingly arranged in the design, which, however, is not entirely successful in terms of both planning and design. Ultimately, it is important to save primary energy , which is only possible through new designs and the associated manufacturing processes. This saving starts with lighter, material-friendly cross-sections and the associated processes in their composition.
New ceiling construction with sandwich cross-section
The current demands to save energy in the building products and in the processes lead to the consequent development of the sandwich cross-section for building ceilings. The effect of the sandwich cross-section in concrete is comparable to lightweight constructions. Two thin shells provide almost the same bending resistance as a full cross-section. The shear resistance is created by the few discrete ribs. One way or another, these are necessary in order to connect the two shells with one another in a non-positive manner. The material-appropriate reduction of the cross-section to the two thin shells and a few ribs saves material and consequently weight. The material savings are up to 55% depending on the span and ceiling thickness. This saves energy and resources during manufacture and consequently less primary energy is used. The reduction in weight and almost the same level of rigidity make it easy to bridge large spans without supports with the slim ceiling cross-section . In conjunction with pre-tensioned reinforcement , which is also lower due to its lower dead weight, large spans with low deflections are produced. Large, column-free rooms allow a very flexible use, as the interior rooms can be adapted and changed as required using light partition walls. This high flexibility ensures the building is highly sustainable.
Integral function utilization through integration of the building technology components within the ceiling cross-section
With the sandwich cross-section, three individual levels are available for the arrangement of the lines. Each of the three levels is intended for a specific arrangement of selected lines. Based on experience, the individual layers of the sandwich cross-section are covered with the pipelines described below. The lower shell is thermally activated with the factory-installed water-guided pipes. Compared to classic component activation , the low concrete mass on the one hand and the near-surface arrangement of the pipes on the other hand lead to a significantly higher thermal performance and a very fast response time. This improvement in performance enables the room to be air-conditioned solely via the ceiling surface without any additional devices such as radiators or ceiling sails. The quick reaction in connection with the high performance also allows individual room control. The prerequisites for the parallel operation of heating and cooling are given with these properties. The absorbers to improve the room acoustics are also integrated flush with the ceiling in the lower shell. The reverberant concrete surface is defused by the special strip absorber. There is also space in the lower shell for empty conduits for electrical cables for connecting equipment under the ceiling . The dimensions of the lower shell must be adjusted accordingly. The middle level, the ceiling void, is freely available for the integration of the ventilation lines , the electrical cables, the supply lines for the zone-wise arranged heating distributors, for the heating distribution boxes themselves and for the sprinkler pipes. However, the ribs must then have openings that are adapted in size to the pipelines at regular intervals for the passage of the lines.
The upper level can be used for other lines such as empty electrical pipes or for water-based pipe registers for possible underfloor heating. I. d. As a rule, the upper level contains recesses for the revision of the ceiling void.
Prefabricated ceiling tiles
Panels with a sandwich cross-section can ideally be produced with prefabricated elements . The lower shell and the associated ribs represent a unit. This construction is produced in the precast plant as a complete unit. The planned building technology components for the lower shell and the ribs are already assembled in the factory. As soon as this unit has been laid on the construction site, the lines can be connected across the panel joints to form a continuous strand. The entire ceiling cavity is available for orderly cable routing.
However, the ribs must also have the openings for the line crossing. With the slim dimensions of the ceiling and its individual parts, little material remains to absorb the internal influences. The stresses around the recesses can only be absorbed with a special form of reinforcement . Depending on the size of the required recess, specially shaped reinforcing steel is sufficient, or a steel sheet as a composite structure generates the required resistance. Thanks to the production in the factory, a precise production and execution of the reinforcement or the composite elements can be guaranteed. A parabolic or trapezoidal cable geometry with subsequent pre-tensioning (pre-tensioning with or without bond) also contributes to the shear force resistance. In this way, the effect of pre-tensioning also relieves the stresses around the openings. As soon as all lines have been connected, extended or supplemented, the upper shell can be installed. As an independent, self-supporting panel unit, it is laid on or between the ribs. The connection details allow a shear-proof connection of the upper plate with the lower unit, so that the sandwich cross-section formed in this way becomes load-bearing as a unit. The unit of cross section produced in this way determines the load-bearing capacity and the serviceability of the entire panel unit.
- Thomas Friedrich: Multifunctional concrete ceilings, Chapter V in Concrete Calendar 2016, ISBN 978-3-433-03074-5
- Ceiling tiles and systems , baunetzwissen.de
- ↑ Th. Friedrich, O. Kornardt, W. Kurz, J.Schnell: Development of a wide-span sandwich ceiling system with integrated building technology in composite construction; Concrete and reinforced concrete construction (2014), issue 1
- ↑ J. Schnell; K. Thiele: Design of reinforced concrete ceilings without shear reinforcement with integrated cable routing; DIBt announcements 4/2011
- ↑ M. Abramski, Th. Friedrich, W. Kurz, J. Schnell: Load-bearing effect of concrete dowels for sandwich composite ceilings with large openings Stahlbau (2010), volume 4