PRESTRESSED PLATE-SHAPED BUILDING COMPONENT AND METHOD FOR THE PRODUCTION OF SUCH A BUILDING COMPONENT

Abstract: A prestressed plate-shaped building component (10) comprises a plurality of elongate laminations (11) of wood, placed in side-by-side relationship and held in contact under pressure with each other in an elastically compressed state by a plurality of mutually spaced transverse tension bars (12) of metal, which extend each through one row of through holes (13) in the laminations (11) and which, at their ends, are provided with anchoring means (14), projecting in lateral directions therefrom and bearing under pressure against cooperating bearing surfaces (15) of the two outer laminations (11), provided at the outer sides of said laminations. The anchoring means are formed by metal plates (14), welded to the tension bars (12) at the ends of said bars.

Description: Prestressed plate-shaped building component and method for the production of such a building component The present invention relates to a prestressed plate-shaped building component. More particularly, the invention relates to such a building component of the kind comprising a plurality of elongate laminations of wood, placed in side-by-side relationship and held in contact under pressure with each other in an elastically compressed state by a plura¬ lity of mutually spaced transverse tension bars of metal, which extend each through one row of through holes in the laminations and which, at their ends, are provided with anchoring means, projecting in lateral directions therefrom and bearing under pressure against cooperating bearing surfaces of the two outer laminations, provided at the outer sides of said laminations . Building components of said kind are utilized especially as structural floor components in buildings and bridges. However, they may be utilized also for other purposes. For instance, they may be used as struc¬ tural wall elements. In previously known building components of said kind, the anchoring means mounted on the tension bars have been formed by nuts, mounted on threaded end por¬ tions of said bars, and washers placed behind said nuts. However, this design of the known building components is unfavourable for several reasons. Firstly, in order to provide the tension bars with threaded end portions, said bars have to be sub ected to special thread cut¬ ting operations. Secondly, these threaded end portions cause a reduction in the feasable tensile strength of the tension rods, as said strength will be determined by the minor diameter of the threads cut and not by the diameter of the smooth main portions of the tension bars located between said end portions. Accordingly, the use of anchoring means consisting of nuts mounted on threaded end portions of the tension bars has an unfavourable influence on the total material and manu- facturing costs of the tension bars. The invention has for its purpose to provide an improved building component of the kind initially spe¬ cified, which makes it possible to reduce the total costs for the tension bars and which, in addition, may be produced m a more rational manner than the building components previously known. The building component, according to the invention proposed for said purpose, is primarily characterized in that the anchoring means are formed by metal plates, welded to the tension bars at the ends of said bars. These metal plates may preferably be welded to the end surfaces of the tension bars in butt contact with said surfaces. In order to make it possible to place two or more building components side-by-side and with adjacent lateral surfaces thereof in contact with each other, the two outer laminations of the building component, proposed in accordance with the invention, may suitably be provided with recesses at their outer sides, in which said metal plates are received in a fully countersunk state . Furthermore, at their outer sides, the two outer laminations may be provided with longitudinally extending grooves, usable for receiving blocks, serving as guide means and force transmitting means between adjacent building components. In this case, said re¬ cesses may advantageously be formed by portions of these grooves . During the production of the abovementioned known building components, the desired elastic compression of the laminations has been obtained by successively tightening the nuts mounted on the various tension bars in several consecutive steps. This has resulted in a manufacturing process which, as a whole, is very slow and labour-consuming. The invention therefore also has for its purpose to provide an improved and more rational method for the production of a prestressed plate-shaped building component of the kind initially specified. The method, according to the invention proposed for said purpose, is primarily characterized by placing the laminations in desired side-by-side positions upon a substrate and subjecting the laminations so placed to an edge pressing operation, during which they are elastically compressed in a direction transverse to their longitudinal direction by means of press aws, bearing against the two outer laminations, and then holding the laminations in an elastically compressed state by means of said press jaws until a lasting elastic compression of the laminations has been secured by means of tension bars, inserted each through one row of holes in the laminations, and anchoring means, mounted at the ends of said bars. During the edge pressing operation, the laminations may preferably be held in close contact with the substrate by holding-down means, applied against the upper sides of the laminations. In order to avoid the need for very long press aws, extending along the entire length of the building component, and in order to make it possible, in an easy manner, during the edge pressing operation, to obtain a convenient access to the outer laminations within the regions of the tension bars and the anchoring means, the edge pressing operation may preferably be performed by means of the two rows of consecutive press aws which, within each row, bear against one of the two outer lamina¬ tions and which, within each row, define intermediate free gaps therebetween, located within the regions of the tension bars and the anchoring means. The insertion of the tension bars through said holes may preferably be effected after the edge pressing operation. Furthermore, the tension bars may suitably be provided with anchoring means at their one ends before the insertion of said bars through said holes m the laminations, while anchoring means are mounted at the other ends of said bars after the insertion of the bars through said holes. In accordance with the invention, the tension bars may preferably be provided with anchoring means formed by metal plates, welded to the tension bars at the ends of said bars. These metal plates may suitably be welded to the end surfaces of the tension bars in butt contact with said surfaces through a flash-welding process . Below the invention is further described with reference to the accompanying drawings, in which:- Figure 1 shows a perspective view of a prestressed plate-shaped building component according to an embodi¬ ment of the invention, selected by way of example, Figure 2 shows a perspective view which only very diagramatically illustrates an edge pressing equipment usable for the production of the building component according to Figure 1 , Figures 3 - 6 show end views, in cross-section, of the building component according to Figure 1, illustra¬ ting different stages during its production, and Figure 7 shows a partial cross-sectional view of two building components according to Figure 1, placed in side-by-side relationship. The building component shown m Figure 1 and gene¬ rally designated 10 comprises a plurality of elongate laminations 11 of wood, placed in side-by-side relation¬ ship and held in contact under pressure with each other in an elastically compressed state by a plurality of mutually spaced transverse tension bars 12 of metal, which extend each through one row of through holes 13 (Figure 3) in laminations 11 and which at their ends are provided with anchoring means 14, projecting in lateral directions therefrom and bearing under pressure against cooperating bearing surfaces 15 of the two outer laminations, provided at the outer sides of said lamina¬ tions. Anchoring means 14 are formed by metal plates having a generally square or rectangular shape, which are welded to the tension bars 12 in butt contact with the end surfaces of said bars. At their outer sides, the two outer laminations 11 are provided with longi- tudinally extending grooves 16, in which metal plates 14 may be received in a fully countersunk state and in contact with the bottom surfaces of said grooves, which form said bearing surfaces 15. Below a method for the production of the building element 10 shown in Figure 1 will be described in further detail with reference to Figures 2 - 6. In Figure 2 there is shown an edge pressing equip¬ ment comprising a press table 17, upon which laminations 11 are placed in side-by-side positions with their one ends in contact with a transverse elongate stop 18 and with one of the two outer laminations in close contact with a row of stationary press jaws 19. The laminations 11, now being in the state illust¬ rated in Figure 3, are then subjected to an edge pressing operation, during which they are elastically compressed in a direction transverse to their longitudinal direc¬ tion by means of a row of movable press jaws 20, which may be applied against the other one of the two outer laminations 11 by means of hydraulic cylinders 21. Through this elastic compression, laminations 11 are brought to assume the state shown in Figure 4. By means of one or more holding-down means, applied against the upper sides of the laminations, laminations 11 are, during the edge pressing operation, held in close contact with press table 17, which serves as a substrate therefor. In Figure 2, a plate 22, serving as a holding-down means, has been indicated in dash- dotted lines. Said plate may be brought into contact under pressure against the upper sides of laminations 11 by any suitable means not shown. The movable press jaws 20 and the cooperating fixed press jaws 19 may preferably be arranged to apply the desired compression pressure to the outer laminations 11 by being brought into close contact with the bottom surfaces of the longitudinal grooves 16 provided in said laminations. Once laminations 11 have been compressed to the state shown in Figure 4, they are maintained in this state by press jaws 19 and 20 while the tension bars 12 are inserted each through one row of holes 16 in laminations 11 in the manner shown in Figure 5. At this stage, tension bars 12 may already be provided with metal plates 14, previously welded thereto, at their one ends. These metal plates, which serve as anchoring means, are brought into close contact with the bearing surface 15 of one of the two outer lamina¬ tions. The other, free ends of tension bars 12 will then project a short distance from the bearing surface 15 of the other one of the two outer laminations. A second anchoring means 14, consisting of a metal plate, is then welded to the latter end of each tension bar 12 through an electric flash-welding process. In order to make it possible to carry out the welding operations in an unobjectionable manner, a porcelain sleeve 23 is mounted in a central position on each plate 14. in order to secure the required access to the outer laminations within the regions of tension bars 12 and anchoring means 14, the fixed press jaws 19 and the movable press aws 20 are designed so as to cause adjacent aws of each kind to define free gaps there¬ between within said regions. Once anchoring means 14 have been welded to all tension bars 12, the compression pressure previously exerted on laminations 11 by means of press jaws 19 and 20 is removed. Laminations 11 then expand slightly to the state shown in Figure 6 and cause an elastic elongation of tension bars 12 which hereby, by means of anchoring means 14, will hold the laminations con¬ tained in building component 10 in a prestressed perma¬ nently elastically compressed state. Figure 7 shows two building components 10 which are located side-by-side and have their adjacent lateral surfaces in close contact with each other. Reference numeral 24 designates blocks of wood, serving as guide means between the two building components 10 and received in portions of the two opposite grooves 16 located between adjacent anchoring means 14.

Claims: C l a ims 1. Prestressed plate-shaped building component ( 10) , comprising a plurality of elongate laminations ( 11 ) of wood, placed in side-by-side relationship and held in contact under pressure with each other in an elastical- ly compressed state by a plurality of mutually spaced transverse tension bars ( 12) of metal, which extend each through one row of through holes ( 13) in the lami¬ nations ( 11 ) and which, at their ends, are provided with anchoring means ( 14), projecting in lateral direc- tions therefrom and bearing under pressure against co¬ operating bearing surfaces (15) of the two outer lamina¬ tions ( 11 ), provided at the outer sides of said lamina¬ tions, characterized in that the anchoring means are formed by metal plates ( 14), welded to the tension bars (12) at the ends of said bars. 2. Building component according to claim 1, characterized in that said metal plates ( 14) are welded to the end surfaces of the tension bars (12) in butt contact with said surfaces. 3. Building component according to claim 1 or 2, characterized in that, at their outer sides, the two outer laminations (11 ) are provided with recesses (16) , in which said metal plates ( 14) are received in a fully countersunk state. 4. Building component according to claim 3, characterized in that, at their outer sides, the two outer laminations ( 11 ) are provided with longitudinally extending grooves (16) , usable for receiving tongues or blocks (24), serving as guide means. 5. Building component according to claim 4, characterized in that said recesses are formed by por¬ tions of said grooves ( 16) . 6. Method for the production of a prestressed plate- shaped building component ( 10) of the kind comprising a plurality of elongate laminations (11) of wood, placed in side-by-side relationship and held in contact under pressure with each other in an elastically compressed state by a plurality of mutually spaced transverse tension bars (12) of metal, which extend each through one row of through holes ( 13) in the laminations (11 ) and which, at their ends, are provided with anchoring means (14), projecting in lateral directions therefrom and bearing under presure against cooperating bearing surfaces (15) of the two outer laminations (11), pro¬ vided at the outer sides of said laminations, characte¬ rized by placing the laminations (11) in desired side- by-side positions upon a substrate (17) and subjecting the laminations so placed to an edge pressing operation, during which they are elastically compressed in a direc¬ tion transverse to their longitudinal direction by means of press jaws (19, 20), bearing against the two outer laminations (11), and then holding the laminations (11) in an elastically compressed state by means of said press jaws (19, 20) until a lasting elastic compression of the laminations has been secured by means of tension bars (12), inserted each through one row of holes (13) in the laminations (11), and anchoring means (14), mounted at the ends of said bars. 7. Method according to claim 6, characterized by holding the laminations (11), during the edge pressing operation, in close contact with the substrate (17) by means of holding-down means (22), applied against the upper sides of the laminations. 8. Method according to claim 6 or 7 , characterized by performing the edge pressing operation by means of two rows of consecutive press jaws (19, 20) which, within each row, bear against one of the two outer laminations (11) and which, withm each row, define intermediate gaps therebetween, located within the regions of the tension bars (12) and the anchoring means (14). 9. Method according to any of claims 6 - 8, characterized by inserting the tension bars (12) through said holes (13) in the laminations (12) after the edge pressing operation. 10. Method according to any of claims 6 - 9, characterized by providing the tension bars (12) with anchoring means (14) at their one ends before the in¬ sertion of said bars through said holes (13) in the laminations (11 ) and mounting anchoring means (14) at the other ends of the bars after the insertion of the bars through said holes (13). 11. Method according to any of claims 6 - 10, characterized by providing the tension bars (12) with anchoring means formed by metal plates (14), welded to the tension bars (12) at the ends of said bars. 12. Method according to claim 11, characterized by welding the metal plates (14) to the end surfaces of the tension bars (12) in butt contact with said surfaces through a flash-welding process. 13. Method according to claim 11 or 12, characterized by providing the two outer laminations (11) with recesses (16) at their outer sides for receiving said metal plates (14) in a fully countersunk state in said recesses.

Inventors: GUSTAFSSON KARL MARTIN, HAEGGLUND KARL SOEREN, JOHNSSON JOHN HAAKAN ARON, GUSTAFSSON, KARL, MARTIN, HAEGGLUND, KARL, SOEREN, JOHNSSON, JOHN, HAAKAN, ARON
Applicants: TRAETEK INST FOER TRAETEKNISK, AB TRAETEK, INSTITUTET FOER TRAETEKNISK FORSKNING
Application year: 1997
Main classification: E01D2
IPC codes: E01D19, E04B5, E04C2