SUPPORTING METHOD FOR HOLLOW-CORE SLABS AND END ATTACHMENT

Abstract: In the method according to the invention an end attachment (1) made of metal is installed at the ends of a hollow-core slab (100). The end attachment comprises a support plate (2) placed against the lower surface of the end portion of the hollow-core slab, a vertical plate (3) attached to a first edge of the support plate (2) in a substantially vertical position, and brackets attached to the vertical plate. A bracket may be e.g. a flat attachment plate (5). The end attachment further includes stiffener plates (12a) to stiffen the structure, and anchoring elements (6) through which the end attachment is attached to the hollow-core slab. The end attachment may be attached to the end of the hollow-core slab already at the element plant immediately after the slab has been cut. The basic idea of the invention is that when the slab is installed on the building site, the slab is not supported directly on the supporting structure but the reaction of support of the slab is transferred onto the beam through the support plate, vertical plate and brackets in the end attachment. With this method of support it is possible to reduce faults occurring from incorrect installation of the hollow-core slab as well as prevent the decrease in the capacity of the hollow-core slab resulting from the bending of the beam.

Description: Supporting method for hollow-core slabs and end attachment The invention relates to a method for attaching a hollow-core slab to a supporting structure such as a beam. The invention further relates to an end attachment of a hollow-core slab and the use thereof. Hollow-core slabs are nowadays commonly used in construction engineering. HoUow-core slabs are rectangular-shaped slab elements manufactured in an element plant and reinforced with prestressing steel strands, having holes, i.e. hollows in the longitudinal direction of the slab. In buildings, hollow-core slabs are supported at their ends by beams made of steel or reinforced concrete or by a load-bearing wall structure so that the lower surface of the end of the slab rests against the surface of the supporting structure. In order to reduce the overall height of the slab structure, so-called ledge beams are commonly employed where a slab rests on a ledge on a side of the beam, close to the lower edge of the beam. Secure attachment of the hollow-core slab to the supporting structure is ensured by installing at the joint the necessary joint and tie bar reinforcements and filling the gaps between the slab and the beam as well as the end portions of the hollows with cement grout cast on the site. There are several disadvantages associated with the prior-art installation method for hollow-core slabs. The making of the joint between the slabs and beams is of great importance to the correct operation of the structure. Now, with the current technique, this work stage has to be carried out in difficult on-site conditions, which adds to the possibility of faults. The position of the end of a hollow-core slab on the ledge of the beam varies due to variations in hollow-core slab lengths and installation tolerances. Placing the end of the slab too close to the edge of the ledge easily results in, particularly in the case of steel beams with thin ledges, that the ledge cannot bear the loads of the hollow-core slab in accordance with the safety margins required by building regulations. This means that a significant part of the loading is transferred onto the beam through the grouting of the end portion of the hollow-core slab. Such a load transfer mechanism affects the bearing capacity of hollow-core slabs and, furthermore, is a method of attachment which is not in compliance with the type approval certificate of hollow- core slabs. As the slabs are loaded the beams supporting the slabs naturally undergo bending. Friction and grouting produce so strong a bond between the beam and the hollow- core slab that deformations in the beam are transferred to the end of the hollow-core slab as well. In the worst case these deformations may decrease the load-bearing capacity of hollow-core slabs down to 30% of the bearing capacity of a slab resting on an unbent support. From the utility model 41 19 it is known a bearer for a hollow-core slab where an end of the hollow-core slab rests on an L-shaped profile. At the ends of the bearer there are support elements by means of which the bearer is supported on adjacent supporting structures. The bearer for a hollow-core slab presented in this solution is thus in fact a short beam used when the end of a hollow-core slab is located at an aperture. The bearer disclosed is used to transfer the loads of a hollow-core slab thus situated onto hollow-core slabs next to the aperture. The hollow-core slabs adjacent to the aperture must be supported from each end on the supporting structures in a conventional way because the solution disclosed cannot be used to transfer loads of a hollow-core slab onto a support structure, such as a beam, at the end of the hollow-core slab. From the patent publication DE-2415213 it is known a reinforced concrete beam which has steel end attachments at its ends. The text and drawings in the publication teach that the end attachment is intended particularly as end attachment for beamlike structures. Moreover, the end attachment disclosed in the said publication is cast into the beam already in the casting stage of the beam. Therefore, the solution is not applicable to hollow-core slabs which are manufactured by casting machines utilizing continuous casting technique. The object of the invention is to provide a new method of supporting a hollow-core slab on a supporting structure, especially on a bending beam. In the invention, hollow-core slabs are supported on a supporting structure by means of an end attachment attached to an end of the hollow-core slab. The method according to the invention can be used to significantly reduce the disadvantages and drawbacks associated with the prior-art method of installation of hollow-core slabs. The method and apparatus according to the invention are characterized by what is specified in the characterizing part of the independent claims. Some advantageous embodiments of the invention are presented in the dependent claims. The basic idea of the invention is as follows: In the method according to the invention a separate end attachment is fixed on one end or both ends of a ready-made hollow-core slab. The end attachment comprises a support plate placed against the lower surface of the end portion of the hollow-core slab, a vertical plate attached substantially in vertical position to an edge of the support plate, and brackets by means of which the end attachment and the hollow-core slab attached thereto may be supported on a supporting structure. The basic idea of the invention is that when the slab is installed on the site it will not be attached by its end direct to the supporting structure, such as a beam, but the reaction of support of the slab will be transferred onto the beam through the support plate, vertical plate and brackets in the end attachment. In an advantageous embodiment of the invention the end attachment is attached to the end of the hollow-core slab already at the element plant immediately after the slab has been cut. An advantage of the invention is that it enhances the operation of the joint between the hollow-core slab and beam because the end attachment provides the hollow-core slab with a fixed and reliable lower support structure. When using an end attach- ment the hollow-core slab is always supported by its lower end, as stipulated in the type approval certificate, and no reaction of support can be transferred onto the beam, at least to a significant extent, through the grouting of the end portion of the hollow-core slab. Another advantage of the invention is that a hollow-core slab equipped with an end attachment can be supported by many kinds of beam structure since the end attachment can be shaped suitable for different beams. Thus the beam need not have a ledge below the hollow-core slab. By means of the end attachment the reaction of support of the hollow-core slab can also be transferred upwards from the lower edge of the beam, say onto the top part of the beam. On top of the beam there is more room for the support structure, greater support widths can be used, and the installation of the slab is easier. A further advantage of the invention is that it makes the installation work of a hollow-core slab quicker, for a hollow-core slab with an end attachment will not require grouting to the same extent as a hollow-core slab attached using a conven- tional technique. Moreover, the grouting is less important from the point of view of the operation of the joint, so the number of detrimental faults decreases. If necessary, a hollow-core slab may be attached to the beam completely without grouting, which means the structures may be realized so as to be easily disassembled. A still further advantage of the invention is that it enhances the load-bearing capac- ity of hollow-core slabs. Because of the end attachment the lower edge of the hollow-core slab is not in direct contact with the bearing beam so that bending in the beam will not cause deformations at the end of the hollow-core slab. Because of the smaller deformations, the bearing capacity of the hollow-core slab is not decreased, which usually happens with hollow-core slabs supported by bending beams. A yet further advantage of the invention is that it is simple in structure, low in manufacturing costs and well suited to industrial manufacture. The invention is below described in detail. Reference is made to the attached drawings in which Fig. 1 shows by way of example a side view of a hollow-core slab supported on a beam and equipped with an end attachment according to the invention, Fig. 2 shows by way of example an advantageous embodiment of an end attachment according to the invention depicted at an angle from the front, and Figs. 3a to 3e show by way of example some advantageous embodiments of an end attachment according to the invention. Fig. 1 shows by way of example in the longitudinal direction a cross section of a hollow-core slab 100 supported on a beam 200 and having an end attachment 1 according to the invention at its end. The hollow-core slab is a rectangular-shaped slab-like concrete building component manufactured at a hollow-core slab plant and comprising two substantially parallel sides, two ends, and an upper surface and lower surface. In addition, the hollow-core slab comprises hollows 102 in the longitudinal direction of the slab as well as longitudinal reinforcements, which usually are prestressing steel strands. Due to the structure of the hollow-core slab the slab is installed in the building practically always in a manner where that surface of the slab which is closer to the main part of the reinforcement of the slab is positioned as the lower surface of the slab. In the description to follow the lower surface of the hollow-core slab refers just to that surface of the slab which in a completed building will be the lower surface of the slab. Conversely, the upper surface of the slab refers to the surface opposite to the lower surface. The end attachment 1 comprises a support plate 2 placed against the lower surface of the end portion of the hollow-core slab, and a vertical plate 3 attached by its edge or surface to an edge of the support plate. Advantageously the vertical plate is as long as the support plate but it may also be shorter and it may be comprised of two or more separate components. The vertical plate is attached to the support plate so that they form an angle which is advantageously a right angle. Thus the support plate 2 and vertical plate 3 together form a profile known as an L profile. The length of the support plate 2 may be advantageously selected such that it extends, on the lower surface of the hollow-core slab, substantially across the whole width of the hollow-core slab, but the length of the support plate may also be something else than the width of the hollow-core slab. The width of the support plate 2 may be selected suitable, however such that the width is at least the support width specified in the type approval certificate of the hollow-core slab. The vertical plate 3 comprises brackets bent at an angle from the plane of the vertical plate. The brackets, which there may be one or more, are elements made of preformed metal plate, bar or pipe, protruding from the plane of the vertical plate and attached at one end or edge to the vertical plate 3, with a second end or edge pointing away from the hollow-core slab. The bracket shown in Fig. 1 is a protrud- ing attachment element 4 attached to a beam 200 so that a side of the attachment element is placed, when installed, against a surface 202 of the beam. Furthermore, the end of the attachment element of Fig. 1 is bent at an angle in order to lock the attachment element 4 onto a locking groove 204 in the beam. The end attachment 1 further comprises an anchoring element 6 through which the end attachment is attached to the hollow-core slab 100. The anchoring element is a rod-like or strip-like protrusion one end of which is attached to the vertical plate 3 and the other end of which extends into a hollow 102 in the hollow-core slab 100. The anchoring element may be a solid part or it may be tubular, in which case its hollow inner section may be used e.g. as an installation conduit for electric cables. The anchoring element is attached to the hollow-core slab advantageously through grouting 8, i.e. by pouring cement grout in the hollow 102. When the grouting has cured the anchoring element 6 and the whole end attachment are firmly attached to the end of the hollow-core slab. It is advisable to install in the hollow 102 plugs 10 shaped to fit the hollow, confining the grouting area to the end section of the hollow. These plugs may be separate parts or advantageously plastic or metal parts integral with the anchoring element 6. The anchoring element may be attached to the hollow-core slab also without grouting, say, by being mechanically wedged against the walls of the hollow 102. The end attachment may be attached to the end of the hollow-core slab also by means of a combination of mechanical attachment and grouting so that the end attachment is first mechanically attached to the end of the hollow-core slab at the hollow-core slab plant, and the hollow-core slab is installed in its place using this mechanical attachment. The fastening of the end attachment is completed on the site by means of grouting in which cement grout is injected in the hollow of the hollow- core slab. Fig. 2 shows by way of example another advantageous embodiment of an end attachment according to the invention depicted at an angle from the front. In order to illustrate the structure of the end attachment the end attachment is shown detached from the hollow-core slab 100. In this embodiment the end attachment comprises a vertical plate 3 of substantially the same length as the support plate 2, and an attachment plate 5 of substantially the same length as the vertical plate. The vertical plate 3 is attached by a first edge to a first edge of the support plate. The attachment plate 5, in turn, is attached by a first edge to a second edge of the vertical plate 3 in a substantially horizontal position so that a second edge of the attachment plate points in a substantially opposite direction than the second edge of the support plate 2. Thus, in this embodiment, the end attachment 1 is attached by means of a single attachment plate 5. At the second edge of the attachment plate there may additionally be a locking edge 7 bent at an angle from the plane of the attachment plate to lock the end attachment onto the supporting structure, such as a beam 200, if the latter comprises a locking groove 204. The end attachment may be manufactured e.g. by forming a single metal plate into a form resembling the Z profile described above or by joining together different metal profiles and/or platelike parts e.g. by welding. The end attachment 1 shown in Fig. 2 naturally comprises also the anchoring elements 6 mentioned in the explanation of Fig. 1, used to attach the end attachment to the hollow-core slab 100. In the embodiment depicted in Fig. 2 the anchoring elements, which advantageously may be deformed steel bars, are attached by a first end to the vertical plate 3 of the end attachment e.g. by welding. Anchoring elements may be attached to the end attachment so that there is an anchoring element in every hollow 102 of the hollow-core slab or only in some of the hollows. Fur- thermore, there may be more than one anchoring element in one hollow. An anchoring element is attached to a hollow 102 in the hollow-core slab by grouting 8, i.e. by pouring cement grout in the hollow. The end attachment 1 shown in Fig. 2 may be equipped with stiffener plates 12a attached by a first edge to the support plate 2, and by a second edge, next to the first edge, to the vertical plate 3. Stiffener plates can be used to enhance the stiffness of the end attachment and prevent the bending of the support plate under loads coming from the hollow-core slab 100. The quantity of stiffener plates can be selected according to the stiffness required of the end attachment. If stiffener plates 12a are used in the end attachment, notches 104 must be made at the end of the hollow-core slab 100 where the stiffener plates are to be attached so that the end attachment may be attached to the end of the hollow-core slab in such a manner that the surface of the vertical plate 3 is placed against the end plane of the hollow-core slab. The cross-sectional drawings of the end section of a hollow-core slab shown in Figs. 3a, 3b, 3c, 3d and 3e illustrate, by way of example, some advantageous embodiments of the end attachment according to the invention. The end attachment of Fig. 3a includes a small triangular stiffener plate 12a which adds the stiffness of the end attachment and prevents the support plate 2 from bending. In addition, the end attachment includes a plug 10 attached to an anchoring element 6, with a gasket 11 made from a flexible material attached to the edge of the plug. The end attachment is attached to the hollow-core slab through grouting 8 which may fill the end of the hollow, confined by the plug 10, either completely or in part. The shape of the attachment plate 5a is an L profile. In the advantageous embodiment of the invention shown in Fig. 3b the end attachment comprises a tall rectangular stiffener plate 12b with a planar projection 14 at the upper edge thereof. In this embodiment the stiffener plate 12b with the projec- tion 14 forms at the same time an attaching means for the end attachment because now the hollow-core slab with the end attachment can be attached to the supporting structure by the projection 14. Thus it is possible to completely or partly leave out the attachment plate of the end attachment. Use of a stiffener plate 12b the height of which equals the height of the whole hollow-core slab requires that notches 104 for the stiffener plate have to be provided also at the upper edge of the hollow-core slab. In the advantageous embodiment of the invention shown in Fig. 3 c the end attachment employs a large polygon-shaped stiffener plate 12c comprising a support bracket 16, which supports the attachment plate 5a, and a fixing bracket 18 extend- ing inside a hollow 102 in the hollow-core slab 100. The width of the fixing bracket may be equal to or smaller than the diameter of the hollow 102. In this embodiment the fixing bracket 18 serves at the same time as an anchoring element 6 so that no separate anchoring element is needed. A plug 10 may be attached at the end of the fixing bracket. In the advantageous embodiment of the invention shown in Fig. 3d the end attachment comprises two substantially rectangular suspension plates 13, the height of which equals the thickness of the hollow-core slab 100, attached in vertical position at opposing ends of the support plate 2 so that the suspension plates are placed against the sides of the hollow-core slab, i.e. in the seams between adjacent hollow- core slabs in a finished structure. In this embodiment the support plate 2 and vertical plate 3 form a single structure but the attachment plate 5b is a separate rectangular flat element located on the upper surface of the hollow-core slab 100, parallel to the plane of the upper surface of the hollow-core slab. The attachment plate 5b. the length of which substantially equals the width of the end section of the hollow-core slab, is connected to the support plate 2 through the suspension plates 13 so that one suspension plate is attached by a first end to a first end of the support plate 2 and by a second end to a first end of the attachment plate 5b. Similarly, the other suspension plate is attached by a first end to a second end of the support plate and by a second end to a second end of the attachment plate 5b. The support plate, attachment plate and suspension plates thus form a ring-like structure around the whole end section of the hollow-core slab. In this embodiment of the end attachment it is also possible to use the stiffener plates 12a depicted in Fig. 3a. In the advantageous embodiment of the invention shown in Fig. 3e the end attach- ment comprises, in addition to the anchoring element 6, a second anchoring element 6b. The both anchoring elements are located in one and the same hollow 102 in the hollow-core slab. The lower anchoring element 6 in the drawing is attached by a first end to the vertical plate 3 and by a second end to the plug 10. The upper anchoring element 6b in the drawing, which is substantially longer than the lower anchoring element, is also attached by a second end to the plug. The upper anchoring element 6b is, however, so long that its first end extends longer than the plane of the vertical plate 3 in the direction of the hollow-core slab. The upper anchoring element is attached at the area between the first and second end to the attachment plate 5c and thus also functions as a support for the attachment plate at the same time. The attachment plate 5c may be a straight flat element, as shown, or it may be an L profile. In the method according to the invention a hollow-core slab 100 is first manufactured using a manufacturing method for hollow-core slabs. An end attachment according to the invention is then attached to an end of a completed hollow-core slab. A completed hollow-core slab refers in this description to a hollow-core slab cast in a hollow-core slab machine onto a casting table and cut into size. The end attachment may be attached to the end of the hollow-core slab on the building site, in storage or advantageously at the element plant immediately after the slab has been cut. The hollow-core slab with the end attachment is installed on the building site so that the support brackets, i.e. the attachment elements 4 or the attachment plate 5. are attached to a supporting structure such as a beam 200. In the invention, the brackets are arranged in the end attachment so that the hollow-core slab may be supported by means of the end attachment on a supporting structure, such as a beam, located specifically at the end of the hollow-core slab. This attachment may be advanta- geously realized so that a surface of the attachment element 4 or attachment plate 5 is placed against a surface of the supporting structure 202. Using this technique, the hollow-core slab itself rests by its lower surface on the support plate of the end attachment and the loads of the hollow-core slab are transferred to the supporting structure through the end attachment. Because the lower surface of the hollow-core slab is not in direct contact with the supporting structure, bending of the supporting structure does not cause deformations diminishing the load bearing capacity to the end of the hollow-core slab. After the hollow-core slab has been installed, the gap between the supporting structure and the end section of the hollow-core slab may be filled with cement grout, if necessary. The method and end attachment according to the invention can be used to support all those hollow-core slabs that reach the support. Above it was described some advantageous embodiments of the method and end attachment according to the invention. The invention is not limited to the solutions described above, but the inventional idea may be applied in numerous ways within the limits defined by the claims attached hereto. For example, the visible portions of the end attachment may be protected against fire by painting them with fire-resistant paint prior to installation.

Claims: Claims 1. A method for supporting a hollow-core slab (100) on a supporting structure such as a beam (200), characterized in that - an end attachment (1) is attached to an end of the hollow-core slab ( 100), - which end attachment includes a flat support plate (2) placed against the lower surface of the end portion of the hollow-core slab, a vertical plate (3) at an edge of the support plate, and brackets (4, 5, 5b), and - the hollow-core slab is supported by means of the end attachment on a supporting structure, such as a beam, located at the end of the hollow-core slab. 2. A method according to claim 1, characterized in that the end attachment (1) is attached to an end of the hollow-core slab (100) by means of anchoring elements (6) in the end attachment, inserted in a hollow (102) in the hollow-core slab (100). 3. A method according to claim 2, characterized in that an anchoring element (6) in the end attachment (1) is attached to the hollow (102) in the hollow-core slab (100) by means of grouting (8). 4. A method according to any one of claims 1 to 3, characterized in that the end attachment (1) is attached to the end of the hollow-core slab (100) prior to the installation of the hollow-core slab. 5. A method according to claim 4, characterized in that the end attachment (1) is attached to the end of the hollow-core slab (100) at the element plant or on the building site. 6. An end attachment (1) of a hollow-core slab (100), comprising a flat support plate (2) placed against the lower surface of the end portion of the hollow-core slab, a vertical plate (3) attached to an edge of the support plate, and brackets (4, 5, 5b) to attach the end attachment to a supporting structure, characterized in that the brackets are arranged so as to be elements in the end attachment protruding from the plane of the vertical plate in order to transfer the reaction of support of the hollow- core slab through the end attachment to a supporting structure such as a beam (200) at the end of the hollow-core slab. 7. An end attachment (1) according to claim 6, characterized in that the bracket (4, 5, 5b) is a protruding attachment element (4) arranged at an edge or surface of the vertical plate (3). 8. An end attachment (1) according to claim 6, characterized in that the bracket is a flat attachment plate (5) arranged at a second edge of the vertical plate (3) bent at an angle from the plane of the vertical plate. 9. An end attachment (1) according to claim 6, characterized in that the bracket is an attachment plate (5b) placed against the upper surface of the hollow-core slab (100), parallel to the plane of the upper surface, and that the end attachment comprises suspension plates (13) placed against the sides of the hollow-core slab, which suspension plates are attached by first ends to the ends of the support plate (2) and by second ends to the ends of the attachment plate (5b) so that the support plate, attachment plate and suspension plates form a ring-like structure around the whole end section of the hollow-core slab (100). 10. An end attachment (1) according to any one of claims 6 to 9. characterized in that the end attachment includes anchoring elements (6) to attach the end attachment to an end of a hollow-core slab (100). 11. An end attachment (1) according to claim 10, characterized in that the anchoring elements (6) are projections attached by a first end to the vertical plate (3) and a second end of which fits into a hollow (102) in the hollow-core slab (100). 12. An end attachment (1) according to claim 11, characterized in that the anchoring elements (6) are arranged so as to be attached to a hollow (102) in the hollow-core slab ( 100) by means of grouting (8). 13. An end attachment (1) according to claim 11 or 12, characterized in that at a second end of the anchoring element (6) there is a plug (10) that blocks the hollow (102). 14. An end attachment (1) according to any one of claims 6 to 13, characterized in that the end attachment includes stiffener plates (12a, 12b, 12c) attached by a first edge to the support plate (2) and by a second edge to the vertical plate (3). 15. An end attachment (1) according to claim 14, characterized in that the stiffener plate (12b) is shaped like a polygon comprising a projection (14) protruding from the plane of the vertical plate (3), through which projection the end attachment can be supported on a supporting structure. 16. An end attachment (1) according to claim 14 or 15, characterized in that the stiffener plate (12c) is shaped like a polygon which comprises a fixing bracket (18) extending into a hollow (102) in the hollow-core slab (100). 17. An end attachment (1) according to any one of claims 6 to 16, characterized in that the end attachment is arranged so as to be attached to an end of a hollow-core slab (100) prior to the installation of the hollow-core slab. 18. An end attachment (1) according to any one of claims 6 to 17, characterized in that the end attachment is made substantially completely from a metallic material. 19. The use of an end attachment (1) according to any one of claims 6 to 18 in the installation of hollow-core slabs (100).

Inventors: NYKYRI PEKKA, NYKYRI, PEKKA
Applicants: NYKYRI PEKKA, NYKYRI, PEKKA
Application year: 2000
Main classification: E04B1
IPC codes: E04B5