Abstract:
The invention relates to a reinforcement element ( 8 ) for load-carrying or load-transferring structural parts ( 12 ). Said reinforcement element has a flat strip segment ( 100 , consisting of a plurality of supporting fibers ( 26 ) which are embedded in a binder matrix ( 28 ) and are aligned parallel to one another and in the longitudinal direction of the segment. According to the invention, the flat strip segment ( 10 ) engages in an anchoring strap ( 18 ) with each of its free ends and is secured on said anchoring straps against the tensile and shearing forces exerted in the longitudinal direction of the segment. This enables the flat strip segment ( 10 ) can be fixed to a structural part ( 12 ) with an impressed pre-stress. The anchoring straps ( 18 ) can be anchored on the structural part ( 12 ) by means of fixing members ( 36 ).

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention concerns a reinforcing element for load-bearing or load-transferring structural components, the reinforcing element comprising a flat strip lamella secured to the surface of a structural component using an adhesive, the flat strip lamella comprising a plurality of reinforcing fibers embedded in a binder matrix and oriented parallel to each other and in the lamella longitudinal direction. The invention further concerns a process for securing this type of reinforcing element to a structural surface. 
     The reinforcing fibers, which are preferably comprised of carbon fiber, impart to the flat strip lamella a greater elastic extensibility. 
     SUMMARY OF THE INVENTION 
     Beginning therewith, it is the task of the present invention to develop a reinforcing element of the above-described type as well as a process for the securing thereof to a structural surface, such that an imprinted tensile stress can be reliably maintained during and after the hardening of the adhesive. 
     The inventive solution is based on the concept, that the flat strip lamella, on the basis of their large elastic extensibility of the reinforcing fibers, are particularly suitable for pre-tensioning and thus for improvement of the structural support relationship to the reinforced structural component. For this, the flat strip lamellas must be connected at their ends to anchor plates, which make possible the introduction of the pre-tensioning into the structural component, or a tensioning beam provided especially for this, during and after the hardening of the adhesive. In order to accomplish this, it is proposed in accordance with the invention, that each free end of the flat strip lamella respectively engages an anchor plate which via securing means is anchored on the structural unit or on a tensioning beam and thereby is secured against tensile and shear forces acting in the longitudinal direction on the lamella. Advantageously, the anchor plates are materially or chemically connected to the lamella ends, and preferably they are adhered to these. A further improvement of the connection between the anchor plates and the lamella ends can be achieved by force fittingly and/or formed fittingly connecting the anchor plates with the lamella ends, preferably by clamping and/or enclosing between two anchor parts. For production of a form-fitting connection, the lamella ends can respectively be provided with a widening and/or thickening, and the anchor plates with a recess for form-fitting reception of the widening and/or thickening. 
     In order to make possible a thin layer adhesive application, it is proposed in accordance with a preferred embodiment of the invention that the anchor plates are comprised of an at least a thin-walled floor part and a, in comparison to the floor part, thick-walled cover plate, externally flat and extending over the breadth of the lamella. Preferably, the cover plate is provided with the recess for reception of the widening or thickening of the flat strip lamella. For this purpose the anchor plates can be formed of two parts, wherein the two anchor parts are either adhered together or held together by screws. 
     A preferred embodiment of the invention envisions that the broadening and/or thickening of the lamella is formed by a divergent splitting of the reinforcing fibers and at the lamella free end, and in certain cases by a widening of the binder matrix in this area. The broadening and/or thickening can, however, also be formed by an application of material, preferably a synthetic resin, on the lamella ends. 
     In accordance with a further preferred embodiment of the invention it is envisioned that the anchor plates, at least in the area of the entry of the flat strip lamella, are elastic. Thereby, it is made possible that the tensile forces occurring in the transition area are maintained at a reliable level, in that the tensions within the end sections are gradually reduced. In order to achieve this, it is of advantage, when the stiffness at the end sections of the anchor plates at the entry points of the flat strip lamella are gradually reduced. This can be achieved for example in that the wall thickness and/or breadth of the cover part and/or floor part of the anchor plate becomes reduced in the end section towards the entry point of the flat strip lamella. The wall thickness of the floor part of the anchor plate at the entry side corresponds with the layer thickness of the adhesive layer provided on the construction component to be secured. 
     In accordance with a further advantageous embodiment of the invention it is envisioned that the anchor plates include an anchoring section adjacent the end sections, which is provided with a transverse bore for passage-through of the anchoring screws situated along the sides beyond of the there secured lamella end. During tightening of the securing screws, the lamella end is clamped between the floor part and the cover part of the anchor plate, so that besides the adhesive connection a force-fitting connection results. For improvement of the adhesive connection, it is of advantage when the lamella ends are adhered on both sides, with the cover part and with the floor part of the anchor plate. 
     A further variant of the invention envisions that the anchor plates include an at least partially flexible tube, preferably with right-angled internal cross-section, and two wedge elements pressed into the tube, and that the respective lamella ends are tensioned between the wedge surfaces of the wedge elements facing each other, and are adhered thereto. In addition, the wedge parts can also be adhered into the tube. A supplemental form-fitting is achieved thereby, that the each other facing wedge surfaces in the lamella longitudinal direction complementary to each other are curved. Therein, it is advantageous, when one of the two wedge elements extends only over a part of the tube length and that the other wedge element on its wedge surface exhibits a preferentially tangential engaging wedge surface which holds the flat strip lamella against the structural side of the tube wall and with this and the flat strip lamella is adhered and/or tensioned. In order to achieve an optimal flexibility of the anchor plates, the tube can be formed as a wrapped tube of glass fiber reinforced plastic. The tube and the wedge elements can be provided with transverse bore holes situated sideways outside of the lamella end for the passage-through of the securing and tensioning screws. In order to increase the flexibility of the anchor plates at the entry side tube end, it is of advantage, when the tube with wedge elements inserted exhibits a reducing wall thickness or breadth at the end section towards the entry side of the tube. 
     According to a further preferred embodiment of the invention, the flat strip lamellas can be acted upon with an electric current. For this, it is advantageous to construct the anchor plates to be electrically conductive such that they form a contact point for the connection of the carbon fibers to a source of electricity. In this manner, it is possible to accelerate the hardening of the adhesive by resistance heating of the flat strip lamella, and to also increase the thermal stability. 
     The binder matrix of the flat strip lamella is preferably comprised of a duroplast, preferably an epoxy resin. In principle, the binder matrix can also be a thermoplast, preferably selected from the group consisting of polyolefins, vinyl polymers, polyamide, polyester, polyacetate, polycarbonate, and thermoplastic polyurethane. The reinforcing fibers can, as already described, be carbon fibers. In principle, the reinforcing fibers could also be aramide fibers, glass fibers, or polypropylene fibers. 
     For maintaining a pre-tension in the flat strip lamella, the lamella ends are first force-, form- and/or materially-(chemically) engaged with the anchor plate. In accordance with a first process possibility, it is proposed that besides this one of the anchor plates is secured to the structural component, for example is screwed in and/or adhered, while the other anchor plate before or after application of adhesive is brought into engagement with a tensioning mechanism associated with the structural component and activated upon by a shear force for achievement of an elastic pre-tension in the flat strip lamella in the lamella longitudinal direction, whereupon the flat strip lamella pre-tensioned in this way is maintained or pressed against the structural component surface until hardening of the adhesive. A second alternative solution envisions that the anchor plates are first fixed to a tension beam with production of an elastic pre-tension in the flat strip lamella, and that the tension beam is pressed or held against the structural component surface with the adhesive side of the flat strip lamella until the adhesive hardens. According to a preferred embodiment of the invention, an electrical current is conducted though at least through a part of the reinforcing fibers during the hardening of the adhesive for heating of the flat strip lamella and the adhesive layer. 
     For production of the form-fitting engagement between the lamella ends and the anchor plates, the carbon fibers can, at the free ends of the previously cut-to-size flat strip lamellas, be freed of adhesive material, preferably using steam, and split apart forming a broadening and/or thickening, and in this condition, be fixed with a viscous, hardenable binder. The carbon fibers freed of binder matrix are thereby preferably spread apart until divergence at the free lamella ends. The carbon fibers freed of binder matrix are for this purpose preferably introduced into an undercut recess in the anchor plate and there positionally fixed and anchored with a binder which is viscous, hardenable, and at the same time serves as adhesive. The anchor plates are, after achieving a predetermined pre-tension, secured to the structural component or tension beam, preferably by screwing or adhering. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be described in greater detail on the basis of the illustrative embodiments shown in schematic manner in the figures. There is shown: 
     FIG. 1 A section through a structural unit, on which a pre-tensioned reinforcing element in the form of a flat strip lamella is secured with an adhesive while utilizing a heating device; 
     FIG. 2 a  A perpendicular section through a securing element in the area of the anchor plate; 
     FIG. 2 b  A section along the dividing line B—B of FIG. 2 a;    
     FIG. 2 c  A section along the section line C—C of FIG. 2 a;    
     FIG. 3 a  A sectional top view on an alternative reinforcing element in the area of the anchor plate; 
     FIG. 3 b  A section along the section line III—III of FIG. 3 a;    
     FIG. 4 a  A perspective representation of a reinforcing element in the area of the anchor plate; 
     FIG. 4 b  A longitudinal section through the reinforcing element according to FIG. 4 a  in the area of the anchor plate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The reinforcing elements  8  shown in the figures are for the supplemental reinforcing of structural components  12  such as, for example, reinforced concrete, wood, or masonry. They are in the form of a flat strip lamella  10  which with its broad side  14  is secured to the outer surface of the structural component  12  with the aid of an adhesive  16 , preferably epoxy resin. 
     The flat strip lamella  10  is in the form of a composite or interconnect structure comprising a plurality of flexible or limp reinforcing fibers  26  oriented parallel to each other, preferably of carbon fiber, and a binder matrix  28 , preferably an epoxy resin, which secures the reinforcing fibers fixed against movement with respect to each other. The binder matrix  28  ensures that the flat strip lamella  10  is stiff elastic. 
     The reinforcing element  8  is provided on each end of the flat strip lamella  10  with respectively one anchor plate  18 . The anchor plate  18  is, in the illustrative embodiments shown in FIG. 2 a  to  c  and  3   a  and  b  comprised of a thin walled floor part  19  and a thick walled cover part  20 . The wall thickness of the floor part  19  of the anchor plate  18  is so dimensioned that it corresponds approximately to the adhesive layer thickness of the flat strip lamella  10  in the final assembled condition. 
     In the embodiment shown in FIG. 2 a  to  c , the reinforcing fibers  26  at the end of the flat strip lamella  10  are separated, forming a broadening and thickening  21  of the lamella end, which end is then seated or introduced in a corresponding recess  32  in the cover part  20  of the anchor plate  22 . The broadening and thickening  21  in the lamella ends can be produced by first removing the binder matrix  28  from the reinforcing fibers  26  using steam and then introducing the reinforcing fibers  26  in the recess  32  of the cover part  20  and fixing thereto with the aid of a binder matrix  28  which simultaneously serves as adhesive. For connecting the floor part  19  and the cover part  20 , both parts are provided with aligned screw holes  34 , which at the same time are intended for securing the anchor plates to the structural component  12  with the aid of high strength screws  36 . 
     For application of the reinforcing element  8  on the structural component  12 , first one of the anchor plates  18  is secured to the structural component  12  by means of screws and then the other anchor plate  18  is brought into engagement by a not shown tensioning mechanism. Then, the anchor plate  18  engaged by the anchor mechanism is pulled in the direction of the arrow  38  and thereby the flat strip lamella  10  is elastically pre-tensioned in a desired amount. The second anchor plate  18  is then, after the pre-tensioning, likewise secured to the structural component  12  and anchored there using high strength screws  36  and adhesives. Then, a flat strip lamella together with the previously applied viscous adhesive  16  is pressed against the construction component outer surface until the adhesive is hardened. 
     In order to accelerate the hardening of the adhesive  16 , the flat strip lamella  10  can be heated with the aid of an electric current. For this purpose, the electrically conductive anchor plates  18  can serve as contact points and, via wiring  21 ′, be connected to a source of current  22  so that an electrical current is conducted through the carbon fibers  26  which contact the anchor plates  18 . The carbon fibers  26  form a heat resistor for heating the flat strip lamella  10  and the adhesive  16 . For monitoring the temperature, a not shown temperature sensor can be coupled to the flat strip lamella, of which the output signal can be used for controlling or regulating the heat output. 
     In the illustrative embodiment shown in FIG. 3 a  and  b , the floor part  19  and the cover part  20  are provided with flat or planar tensioning surfaces, which are adhered to each other and to the flat strip lamella  10  lying therebetween. The floor part  19  and the cover part  20  are comprised of a flexible plastic or synthetic material, for example a glass fiber reinforced plastic. The anchor plate is divided into a broader reinforcing section  40  provided with transverse bore-holes  34  for the through-put of securing screws, and an end section  44  which, going towards the entry point  42  of the flat strip lamella  10 , narrows both in wall thickness and in breadth. The reduced thickness and breadth of the floor part  19  and the cover part  20  in the area of the end section  44  has as a consequence that the stiffness of the flexible plate is continuously reduced approaching the entry side  42 , so that strains or tensions in the lamella, which result from the introduced tensile or pull forces, are gradually diminished in this area. Thereby it is ensured, that no impermissibly high pull forces occur between lamella and anchor, which could lead to a premature leasing of the lamella. 
     In the illustrative embodiment shown in FIG. 4 a  and  b , the anchor plate  18  is comprised of a wrapped tube  46  of a glass fiber reinforced plastic with right-angled inner cross section as well as two preformed wedge elements  48 ,  50 , which likewise can be formed of glass fiber reinforced plastic. The wedge surfaces  52 ,  54  of the wedge elements  48 ,  50  facing each other are so curved complimentary to each other in the lamella longitudinal direction that the flat strip lamella  10  tensioned and adhered between them is guided between the wedge surfaces without wrinkling or kinking. One of the two wedge elements  48  extends only over a part of the wrap tube  46 , while the other wedge element  50  exhibits a planar or flat partial surface  58  holding the flat strip lamella against the construction component side of the tube wall  56  such that it is adhered and tensioned thereto. Thanks to the substantially free selectability of the arrangement of the fibers in the wrap tube  46  and the incline or taper provided on the entry side end  42  it is also possible to here adjust the distribution of stiffness of the anchor plate. The curvature of the flat strip lamella  10  which becomes greater going from the entry side  42  towards the end furthest removed from the load, and the adhering and wedging between the lamella and the wrap tube, results in a reliable, form-fitting anchoring of the anchor plate to the flat strip lamella. The wedge elements  48 ,  50  are supplementally fixed in their position with respect to the wrap tube  46  via the through-going securing bore holes  34 . 
     In summary, the following is to be concluded: The invention concerns a reinforcing element  8  for load-bearing or load-transmitting structural components  12 . The reinforcing element includes a flat strip lamella  10 , which is comprised of a plurality of reinforcing fibers  26  which are which are embedded in a binder matrix  28  and run parallel to each other in the lamella longitudinal direction. In order to be able to secure the flat strip lamella  10  to the structural component  12  with an imprinted pre-tension, the lamella engages with both of its free ends in respectively one anchor plate  18  anchorable to the construction component  12  by means of securing means  36 , and the lamella is secured in the anchor plate against tensile and sheer forces occurring in the lamella longitudinal direction.