CONCRETE SLAB WITH INTEGRATED INSTALLATIONS
Transcrição
CONCRETE SLAB WITH INTEGRATED INSTALLATIONS
CONCRETE SLAB WITH INTEGRATED INSTALLATIONS 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] SUMMARY 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. 1. INTRODUCTION 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. 1 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 2. LAYOUT OF THE SPECIMENS 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 system. 2 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). 3. PRODUCTION OF SPECIMENS 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 3 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 elements. 4. EXPERIMENTAL RESULTS 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. 4 Fig 7: Specimen 2 during testing. Fig 8: The failure of specimen 2 after ultimate load. 5. CONCLUSIONS 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. 6. ACKNOWLEDGEMENTS 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. 7. REFERENCES 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. 5