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The invention relates to a precast slab which includes both a slipform-cast ribbed slab and building service systems, wherein the slipform-cast ribbed slab includes a spine and ribs. The invention also relates to a method for manufacturing a precast slab and to a building formed of precast slabs.
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In the prior art, the intermediate and top floors of office and residential buildings are generally formed of hollow-core slabs that are arranged next to one another. An intermediate-floor structure is used in buildings of two or more storeys, wherein the intermediate-floor structure is the ceiling of the lower storey and the floor of the upper storey. A suspended ceiling is subsequently installed underneath the load-bearing structure forming the intermediate or top floor. An intermediate or top floor is usually formed of hollow-core slabs. Necessary building service systems - such as air-conditioning ducts, heating- and cooling-fluid circuits, electrics, and telecommunications cables - are subsequently installed between the hollow-core slab and the ceiling. The ceiling is also called a false ceiling or a dropped ceiling.
European patent 3517698B1 discloses an intermediate-floor slab inside which building service systems are arranged in a prefabrication step. A separate ceiling is thereby unnecessary or at least substantially shallower than to date.
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The ceiling takes up part of the height of a room. Construction of the ceiling is also slow, and in particular the installation of building service systems is awkward on a construction site under construction-site conditions. Work requires the use of scaffolding or hoists, which makes it difficult to work ergonomically. Components must also be carried and elevated a lot. When building service systems in the building framework reach the end of their life cycle, the building framework often also has to be partially pulled down even though it is not yet even close to the end of its life cycle. The repair of building service systems arranged inside an intermediate-floor slab requires a partial breaking of the structure of the intermediate-floor slab. Local repairs are possible, but larger repairs require the removal of the entire slab, as the load-bearing capacity of a broken intermediate-floor slab is diminished. In practice, it is often very difficult, if not impossible, to repair building service systems arranged inside an intermediate-floor slab.
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An object of the invention is to provide a novel precast slab in which building service systems can be modified without breaking a load-bearing structure. A further object of the invention is to provide a novel industrial method for manufacturing a precast slab, which is fast, by means of which manufacturing costs can be kept reasonable, and which permits good working ergonomics. A still further object of the invention is to provide a novel building formed of precast slabs, in which building service systems can be accessed without breaking load-bearing structures, so that the building can be modified in a flexible manner. The characteristic features of a precast slab according to the present invention are set out in claim 1. Analogously, the characteristic features of a method according to the invention are set out in claim 6, while the characteristic features of a building according to the invention are set out in claim 13. The precast slab according to the invention has a new and surprising structure which renders possible both an installation of building service systems and a modifiability of the building service systems after the installation of the precast slab. With the method, manufacture of the precast slab is fast, and the installation of building service systems can be carried out ergonomically at the factory. Quality is also improved due to better working conditions and a better working position. The building service systems in the finished building are inside the precast slab, yet still accessible and modifiable.
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The invention is described in detail in the following with reference to the accompanying drawings illustrating embodiments of the invention, wherein
- Figure 1a
- shows an end view of a precast slab according to the invention during manufacture, without building service systems,
- Figure 1b
- schematically shows a precast slab according to the invention that is part of a building, with building service systems installed,
- Figure 2a
- shows a slipform-casting step of a method according to the invention,
- Figure 2b
- shows a processing and outfitting step of a method according to the invention,
- Figure 2c
- shows an initial part of a rotation step of a method according to the invention,
- Figure 2d
- shows a middle part of a rotation step of a method according to the invention,
- Figure 2e
- shows a final part of a rotation step of a method according to the invention,
- Figure 3
- shows a precast slab according to the invention during rotation without building service systems,
- Figure 4a
- shows lifting locations during the manufacture of a precast slab,
- Figure 4b
- shows lifting points of a completed precast slab,
- Figures 5a-g
- show the lifting of a precast slab during manufacture,
- Figure 6
- shows building service systems of a building, installed inside precast slabs according to the invention,
- Figure 7
- schematically shows a part of a building according to the invention,
- Figure 8a
- shows a part of a building according to the invention prior to a space modification,
- Figure 8b
- shows the part shown in Figure 8a after the space modification.
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The precast slab is primarily intended to form an intermediate or top floor structure in a building. It is also possible to use precast slabs, for example, in the base floors of crawlspaces or as technical floors in, for example, data centres. The factory-manufactured precast slab 10 includes both a slipform-cast ribbed slab 13 and building service systems 14, wherein the slipform-cast ribbed slab 13 includes a spine 11 and ribs 12. Figure 1a shows a slipform-cast ribbed slab 13, including part of a reinforcement 15 and prestressed strands 16 belonging to the slipform-cast ribbed slab 13. Figure 1a shows the ribbed slab before installation of the building service systems. The precast slab 10 of the invention is open on the side that lies opposite the spine 11, and the precast slab 10 is configured to be installed with the spine 11 on top. When the precast slab is installed in this manner, the ribs face downwards. In other words, a cover according to the prior art is not cast in the ribbed slab, and the ribbed slab is cast upside down, which renders possible the installation of building service systems at the factory. As shown in Figure 1b, the precast slab 10 is also installed in a building with the ribs facing downwards. The surprising structure and usage of the precast slab yields several advantages, which will be explained in more detail later on.
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Figure 3 shows a ribbed slab 13 of a precast slab according to the invention that has already been processed following slipform casting. In the invention, the ribs 12 have an abundant number of openings 17 for building service systems 14, the openings 17 being aligned both between the ribs 12 and between adjacent precast slabs 10. In Figure 3, there are two sets of five openings in each rib, wherein the openings are at the same location in the rib in all ribs. In other words, openings are essentially at the same location in adjacent ribs. Building service systems can thereby be guided inside the precast slab both between the ribs as well as across the ribs through the openings when the openings in adjacent precast slabs are essentially at the same location. For example, in Figure 4b, openings 17 are evenly spaced along almost the entire length of the precast slab 10. Building service systems can thereby extend over the entire area of the building.
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Air-conditioning ducts, for example, require large openings, so that a height of the precast slab is greater than that of a conventional hollow-core slab. A greater room height is nevertheless achieved, as a dropped ceiling can be omitted. Along with an increased height, it has simultaneously been possible to increase the length of the precast slab even though the ribbed slab is left open. Where necessary, spaces that are wider than before are thus possible in a building without affecting support points. The ribbed slab of the invention is prestressed and has a length L of 1000 - 20000 mm, a height H of 350 - 800 mm, and a width W of 1000 - 3000 mm. A mass of such a solid precast slab can be as high as 23000 kg. For example, in a precast slab 650 mm high, a diameter of the openings is 350 mm, even 400 mm. A 250 mm ventilation duct, even when insulated, thus fits into the opening. Generally speaking, all necessary building service systems - which include both heating, water, and ventilation ducts and electrical and telecommunications cables - are arranged inside the precast slab. There is even room for additional conduits.
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The precast slab needs to be handled both during manufacture as well as later during storage, transport and on the construction site. Some of the openings 17 in the ribs 12 can be configured as lifting locations 18 for lifting the precast slab during manufacture. In addition to the reinforcement of the rib, the openings in question have an auxiliary reinforcement for increased strength. It is not possible to implement corresponding reinforcements and auxiliary reinforcements in a known hollow-core slab. It is also not possible to make openings in the columns between the cavities of a hollow core.
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When the ribs face upwards, the ribbed slab is lifted by the middle part at two locations, as shown in Figure 4a. During manufacture, the ribbed slab, which has not yet hardened, can only be lifted by the middle, as the prestressed strands pull the ends of the ribbed slab upwards. An even loading of all ribs at the lifting locations is achieved when a transverse lifting bar 19 is used which is cylindrical or which at least has an upper curvature in accordance with the openings. This simultaneously prevents the formation of point loads in the openings. The still damp precast slabs can thereby withstand being moved during manufacture. If necessary, two overhead cranes are used at the same time, as well as possible lifting bars between the lifting locations.
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Analogously, lifting points 20 are arranged on the ribbed slab 13 on the side of the spine 11, the lifting points 20 being arranged in the end portions of the precast slab 10. When the ribs face downwards, the precast slab can withstand such a load when it is lifted by the ends. The lifting point, such as an anchor, is integrated in a rib, so that multiple lifting points are provided in order to achieve an adequate load-bearing capacity. The use of two overhead cranes is advantageous here as well. The precast slab is lifted by the lifting points both at the slab factory as well as on the construction site.
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Figures 2a - 2e schematically show a method according to the invention for manufacturing a precast slab. In the method, a ribbed slab 13 that includes a spine 11 and ribs 12 is cast with a slipform. Figure 2a illustrates the slipform-casting machine 21 as a dashed rectangle. Building service systems 14 are subsequently installed in the slipform-cast ribbed slab 13. In the invention, the precast slab 10 is left open on the side that lies opposite the spine 11, and the precast slab 10 is configured to be installed with the spine 11 on top. The ribs thus face downwards. The ribbed slab can thus be manufactured on an industrial scale, which expedites manufacture and reduces costs. Moreover, building service systems can be accessed without breaking load-bearing structures in the finished precast slab.
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In Figure 2b, the precast slab 10 has already been lifted off the casting platform 22 using the openings. In the invention, prior to the final hardening of the slipform casting, an abundant number of openings 17 is formed in the ribs 12, wherein building service systems 14 are installed in at least some of the openings 17. Building service systems are also installed between the ribs so as to run in the longitudinal direction of the precast slab. For example, a hole saw 23 is used to form the openings. In Figure 2c, the building service systems 14 have already been installed between the ribs 12. Furthermore, in the invention, after the installation, the precast slab 10 is turned over onto the ribs 12 to harden. In practice, the four main steps in the manufacture of the precast slab are slipform casting, forming the openings, installing the building service systems, and transferring the precast slab onto a flipping platform and turning it over. In Figure 2b, the flipping stage 24 is beside the casting platform 22, while in Figures 5a-g the flipping stage 24 is at the end of the production line. As shown in the figures, the precast slab is rotated a full 180 degrees. When the ribs face upwards, the installation of building service systems is easy and ergonomic. The rotation renders possible the final hardening of the precast slab and, ultimately, the modifiability of building service systems that are part of the building. The construction of the building itself is likewise quick, ergonomic, and safe. The number of necessary joining operations that must be carried out on the construction site is much lower than in known construction methods. It also obviates the need to carry components up to the floors.
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The precast slab according to the invention is exceptionally cast upside down using a slipform-casting method so that the spine lies against the casting bed and the ribs face upwards. The arrangement of the prestressed strands of the precast slab at the upper edge of the ribs instead of at the spine is also exceptional. This makes it possible to start with the installation of building service systems shortly after casting, as the precast slab is immediately in the correct position for installation processes. This makes the manufacturing process and the casting cycle faster. Slipform-casting technology also makes it possible to implement larger openings as well as the auxiliary reinforcements they require, both in the ribs and in the spine, on an industrial scale.
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A special flipping stage 24 developed for turning over a massive precast slab is used for the rotation, wherein the flipping stage 24 supports the precast slab during the entire rotation without damaging the ribbed slab or the building service systems. A continuous support is important due to an incomplete hardening and thus limited load-bearing capacity. After the rotation, the precast slab can be lifted by the lifting points at the ends, as shown in Figure 4b .
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The ribbed slab 13 is thus slipform-cast on a casting platform 22 with an industrial slipform-casting machine. Figures 5a -5g show a final part of the casting platform 22 as well as a flipping stage 24 arranged as an extension of the casting platform 22. Preferably, multiple ribbed slabs are slipform-cast successively, so that the slipform platform is several tens or even hundreds of metres long. The flipping stage here is configured for one precast slab. In Figure 5a, the precast slab 10 has been completed. In other words, the ribbed slab has been cast, and the building service systems have been installed, i.e. the precast slab has been outfitted. A slab panel has also been cut off from the ribbed slab. The installation of the building service systems is consequently carried out on the casting platform as soon as it is possible. This reduces the time of manufacture. Once the precast slab has been outfitted and can withstand being lifted, the precast slab 10 is lifted onto the flipping stage 24 following the installation of the building service systems 14. In Figure 5b, lifting mechanisms 25 are attached to openings and, in Figure 5c, the precast slab 10 is lifted vertically. If necessary, further lifting points are used. In Figure 5d, the precast slab 10 is moved horizontally and positioned in the right place over the flipping stage 24 (Figure 5e). Finally, the precast slab 10 is lowered onto the flipping stage 24 (Figure 5f), and the lifting mechanisms 25 are detached. The precast slab is subsequently turned over by means of the flipping stage, and the finished precast slab is moved to storage for hardening.
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In the invention, the slipform casting occurs with low-carbon concrete and the openings are formed within the first 24 hours, preferably within the first 1 - 10 hours, of the slipform casting. Low-carbon concrete contains significantly less water and cement than wet concrete, but slightly more than semi-dry concrete. This results in fewer carbon dioxide emissions, which makes concrete construction more environmentally friendly than to date. The ribbed slab also hardens quickly, so that it is possible to begin processing and outfitting early, in practice on the same day. The synchronized method for manufacturing the precast slab makes it possible to use low-carbon concretes without increasing manufacturing time, as the time it takes the concrete to harden is used to outfit the precast slab. In practice, one begins with the formation of the openings immediately, so that there is time to form hundreds of openings. Fasteners 26, which are installed when the concrete is damp, are provided for the building service systems. In practice, the openings can be formed and the fasteners installed at the same time, which expedites manufacture. The installation of the building service systems begins after the installation of the fasteners.
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As mentioned in the foregoing, prestressed strands 16 are provided in the ribbed slab 16, which prestressed strands 16 are gradually released within the first 48 hours after slipform casting and the installation of the building service systems 14. As the precast slab hardens, the concrete adheres to the strands and retains the tension when the strands are released. Outfitting can continue simultaneously. Finally, the ends of the precast slab are sawn to an exact length.
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When the flipping stage is at the end of the casting platform, the last precast slab is conveyed more than 100 metres horizontally. Such a casting platform can accommodate a plurality of precast slabs according to the invention at a time. A lifting distance can be reduced by forming the flipping stage so as to be movable right up to the side of the casting platform. With the method according to the invention, the ribbed slabs can be slipform-cast on an industrial scale before being outfitted from above already at an initial stage of hardening. Finally, the precast slab is turned over, at which point the precast slabs are almost complete. After finishing and inspection, the slabs are taken to storage to harden. When they are part of the building, the inverted precast slabs render possible an easy modification of building service systems and, before that, a rapid construction.
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The standardized formation of openings and installation of duct systems and other building service systems in the slipform-cast ribbed slab according to the invention can occur within a tight timetable at the factory. While slipform casting per se is known, the outfitting according to the invention and in particular the inversion of the precast slab are new and surprising. The manufacturing process is based on a two-day cycle according to the invention in which a new batch of ribbed slabs is cast every other day. The formation of the openings in the ribs can begin, when the concrete is hard enough, already on the first day. Outfitting can also begin that same day and be continued on the second day. The release of the strands, the sawing of the precast slabs, and finally the turning over of the precast slabs also occur on the second day.
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Figure 6 shows the building service systems 14 of the building that are located inside the precast slabs 10. The contours of the precast slabs 10 are illustrated by dashed lines here. In the example, the precast slabs 10 extend from one end of the building to the other except at the site of three flues 27. Preferably, a flue has the width of a single precast slab, so that short precast slabs can be supported on full-length precast slabs without additional support structures. More long precast slabs are thus provided than conventionally. The flue has vertical ducts that are connected to corresponding ducts in the precast slab. The hookup of the building service systems of the precast slabs is performed on the construction site. This can occur quickly, however, as the whole building service systems are all ready inside the precast slabs. As building service systems, for the sake of clarity, Figure 6 mainly only shows air-conditioning ducts and ceiling-radiator fluid circuits. In Figure 6, the lowermost flue 27 is two slabs wide.
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Figure 7 shows a building which includes at least one intermediate floor 29 supported on a support structure 28. The intermediate floor is formed of precast slabs 10 that are arranged next to one another. The precast slab 10 according to the invention, in which the building service systems 14 are integrated, is used as a precast slab. Each precast slab 10 is installed with the spine 11 on top. The ribs thus face downwards. In addition, the precast slab 10, which is open on the side that lies opposite the spine 11, is covered by a structure 30 which is attached in a detachable manner in order to provide building service systems 14 that can be modified in a flexible manner over the life cycle of the building. The structure 30 is shown in Figure 1b and can be, for example, a suspended ceiling panel that has acoustic, fire-safety, and visual properties. The structure varies as needed. The suspended ceiling panel can be attached to the ribs in a suspended manner. A suspended ceiling panel is an interior decorative element that dampens sound and prevents fire from spreading. A fire-proof panel is only needed in the highest fire-safety classes. If necessary, fire-proof panels are also installed on the sides of the ribs and at the base of the spine. The upper surface of the precast slab does not require fireproofing when insulated with a surface casting. The tendons of the ribs are the most vulnerable to a fire below. The precast slab can still withstand a fire for over an hour even without fireproofing. When it is protected by fire-proof panels, the precast slab can withstand fire for closer to three hours.
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During construction, the precast slabs are lifted onto supporting structures 28 such as, for example, a steel or concrete pillar-and-beam structure. The precast slab is only supported at its ends. In Figure 7, the short precast slab in the foreground is supported at the site of a flue 27 by a load-bearing concrete element 31. Alternatively, short precast slabs are supported by adjacent slabs, which renders possible a flexibility in the modification of building service systems also around flues. This is the case of the short precast slab in the background. The vertical ducts in the flues are connected to a precast slab and via this precast slab to other precast slabs of the same floor. Other system components, such as air diffusers and radiators, are installed underneath, as is the detachably attached covering structure. A storey height 35 of the building according to the invention is formed by a room height 36 and a height H of the precast slab 10. When a dropped ceiling is omitted, the surface areas of the facade side and of the inner walls are reduced by up to 10 % compared to what is known conventionally. It is thus possible to fit eleven storeys in what would normally be a ten-storey building or, alternatively, ten storeys in what would normally be a nine-storey building.
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Figures 8a and 8b show part of a floor plan of an office building in which two rooms 32 and 33 are visible. There is an assumed need here to move the inner wall 34 between the rooms 32 and 33, thus increasing the size of one room and decreasing the size of the other. Figures 8a and 8b show how the ventilation ducts and terminals are to be rearranged in connection with this change. What is essential here is that the changes to the building service systems can be carried out in the integrated structure of the precast slab without having to break the precast slab, which produces a flexible modifiability. It is currently likewise possible in a normal office conversion to make changes to building service systems without breaking an intermediate-floor slab, because the building service systems are located underneath the intermediate-floor slab within the suspended ceiling, contrary to the invention. In a building according to the invention, it is sufficient to move the inner wall and lengthen and/or shorten the ventilation ducts.
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The precast slab according to the invention renders possible a modifiability of building service systems. In other words, the building can be modified in a flexible manner, so that building service systems can be changed during the life cycle of the building. Repair and modification work can be carried out easily from below without breaking load-bearing structures. At the same time, a height advantage is achieved, especially for apartments, as a separate suspended ceiling can be omitted. The manufacture of the precast slab itself is also efficient and ergonomic.
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Modification flexibility includes three main principles, which are versatility, modifiability, and extendibility. Versatility is defined as the ability to adapt to different functions or purposes through small changes. Modifiability is defined as the ability to adapt to a substantial change in the needs of the user through changes to a space. Modifiability is close to versatility, but modifiability allows for a future change in the needs of the user. Extendibility is defined as the property that renders possible a considerable addition of new spaces or new properties or a significant improvement in performance. The precast slab according to the invention in particular renders possible a modifiability without the breakage of structures.