Andreas E. Kainz, Stefan L. Burtscher, Johann Kollegger
Vienna University of Technology – Institute for Structural Engineering, Austria
A-1040 Wien, Karlsplatz 13/212
[email protected]
A new slab system was developed, which allows large and easily accessible installations. This
goal was achieved by integrating the building services into the slab structure instead of a
suspended ceiling or false floor. The load carrying structure consists of a thin concrete slab
connected to girders on the upper side. The girders are produced with large openings, to
produce ducts for the installations. On top of the girders plates that can be removed establish
the floor. Therefore the installations are easily accessible. Since the installation is integrated
into the slab structure the load carrying structure can be higher than in conventional floor
systems, while the overall height is still smaller. The increased structural height allows for
larger spans.
At the Institute for Structural Engineering an optimized slab system for department stores,
industrial and office buildings is under investigation. For such buildings a lot of installations
are necessary and a high degree of flexibility is desirable. The developed slab system is
considering these high requirements and the improvements in contrast to conventional
systems are
reducing the overall height of the load carrying and installation parts.
easier accessibility and higher flexibility of the installations.
allowing for larger spans.
lower self weight.
Installation in conventional slab systems are discussed first. The schematic representation of
the systems discussed, is given in Figure 1. Most often the installations are positioned in the
floor construction embedded in a layer of sand. The disadvantage is that the floor has to be
destroyed, when the installations have to be accessed. Another more flexible option is to
produce a false floor system, where the floor can easily be removed. Then, the accesses and
the repositioning of the installation is easy. When installations with large dimensions are
required a suspended ceiling is usually chosen. A high degree of flexibility and easy accesses
are possible.
The load carrying components and the space that is occupied by the installations are existing
independently of each other. In order to keep the overall height small in conventional systems
it is necessary to optimize both parts independently.
Fig 1: Installations in different slab systems
a) Installations in a layer of sand b) false floor system c) slab for installation
d) Slab with a suspended ceiling e) slab for installations for large installations
This is in contrast to the new system proposed, where the space occupied by the installations
is integrated into the plate. The load carrying structure can be much higher, while the overall
height can still be lower than in conventional systems. The load carrying structure is not made
of a massive plate, but is made up of a girder grid with a plate on the bottom. The girders can
have the form of a framework with large openings. Figures 1c and 1e show one example for
small installations and another for large installations. In Figure 2 a point supported slab with a
girder grid and a thin plate at the bottom is shown. The girders show large openings to
produce ducts for the installations. The girders are covered with plates, that are usually used
for false floor systems and can be easily removed.
Fig 2: Slab for installations
In cooperation with Katzenberger Beton- und Fertigteilwerke GmbH, Graz and Gerasdorf, the
slab system was designed, produced and tested. The length of the specimens was 16.80m and
the width 2.40m. The specimen 1 and 2 represent parts of a point supported slab, where the
slab is founded on three supports, see Figure 3. Specimen 1 has one main span direction (Fig.
3, left), while specimen 2 (Fig. 3, right) shows a grid girder in two span directions. The load
was applied to the specimens in 6 locations, to simulate realistically the forces from the slab
Fig 3: Point supported slab system with specimen 1 (left) and 2 (right) colored in red and
applied force positions.
Specimen 1 consists of one main girder made of reinforced concrete with a height and width
of 40cm. The cross section of the openings is 0.2m². The thickness of the plate was 10cm. The
grid girders of specimen 2 have the same dimensions in both span directions with a height of
40cm and a width of 14cm. The girders also contain steel profiles that were used as formwork
during production. The thickness of the profiles was 4mm. Figure 4 shows a view of the
girders of specimen 1 and 2 before testing.
Fig 4: Cross sections of specimen 1 (left) and specimen 2 (right).
The specimens were produced of 7 prefabricated elements with dimensions of 2.40x2.40m.
Figure 5 shows the prefabricated elements of specimen 1 and 2 positioned in a row and the
reinforcement for the connection. The elements of both specimens were produced with a 5cm
thick reinforced concrete plate. The connection was established on site with reinforcement
bars and another 5cm of concrete. At the final stage the thickness of the concrete plate was
10cm. The girders of specimen 1 were produced similar to the plates by adding concrete and
reinforcement bars on the top of the girder. For the connection of the girders it was necessary
to produce a formwork on site. The girders of specimen 2 were made of steel profiles that are
welded together. The connection between the prefabricated elements was made also on site
with reinforcement bars and concrete. The steel profiles served as formwork and were filled
with concrete over the whole girder height. Figure 6 shows the specimens after connection of
the prefabricated elements.
Fig 5: Prefabricated elements of specimen 1 (left) and 2 (right) before casting with concrete.
Fig 6: Specimen 1 (left) and specimen 2 (right) after connection of the prefabricated
Figure 7 shows specimen 2 under high loads. Due to the high construction height, the large
openings and the layout of the reinforcement shear was more critical than bending. The
transfer of shear forces in the girder was critical due to the large openings. The failure in
specimen 1 occurred close to the opening. Specimen 2 contained a higher amount of shear
reinforcement and the concrete failed in compression at very high loads. The failure was at
the upper side of the girder at midspan, see Figure 8.
Fig 7: Specimen 2 during testing.
Fig 8: The failure of specimen 2 after ultimate load.
The investigations showed that the concrete slab with integrated installations is able to satisfy
high demands on flexibility of the installation and is also able to house installations that
require a large space at a low overall height. Due to the low self weight and the high
construction height large spans up to 10 or 12m can be built at low cost with high quality.
The authors like to thank Fa. Katzenberger Fertigteilwerk GesmbH, for the production of the
prefabricated elements and the Österreichische Forschungsförderungsgesellschaft mbH (FFG)
for funding the project.
Kollegger, J., Kainz, A. E., and Burtscher, S. L. (2006). „Flächige Beton - Tragkonstruktion
sowie Verfahren zur Herstellung derselben.“ Austrian Patent application.
Kollegger, J., Kainz, A. E., and Burtscher, S. L. (2007). „Flächige Beton - Tragkonstruktion
sowie Verfahren zur Herstellung derselben.“ PCT Patent application.