Reinforcing body made of fiber-reinforced plastic

The present invention relates to a reinforcing body for structures, according to the preamble of claim 1, preferably for structures made of concrete or of other hydraulically setting materials, which may also be mixed with other materials, for example with ground materials. The reinforcing body comprises a plurality of reinforcing rods each consisting of fiber-reinforced plastic and connected to one another at connecting points by connecting agents. The individual reinforcing rods can be of any length and cross-sectional shape, and have end portions of any shape. The reinforcing rods preferably have a round, in particular at least approximately circular cross-section and an axial extension that is at least substantially straight.

The use of reinforcing bodies is generally known. They are used to increase mechanical strength, in particular for increasing the tensile strength of concrete structures. Concrete is a principal component of many structures, for example of buildings or bridges. However, in order to withstand the stresses that arise during use, it is essential that reinforcing struts, especially reinforcing struts that transfer tensile forces, be embedded as reinforcement in the concrete. Steel reinforcing rods and reinforcing bodies have proved over many years to provide suitable reinforcement of concrete buildings.

However, steel reinforcements can corrode in situations where the working conditions are particularly tough, especially in damp or chemically aggressive environments. Corrosion of the steel reinforcements leads to a reduction in the adhesive forces and/or to deterioration in the bedding between steel and concrete, which results in cracks and in flaking of the concrete. Not only does this cause an unaesthetic appearance of the buildings affected, but the corrosion of the steel reinforcements can lead above all to weakening and ultimately even to final collapse of the structure, thus signifying a major hazard. Due to the damage caused to structures by corrosion, substantial levels of repair and maintenance expense are necessary in order to avoid any further risks.

Reinforcement with non-corroding or corrosion-resistant reinforcing struts, for example with reinforcing struts or reinforcing bodies that are galvanized or epoxy-coated or made of stainless steel, are known as a means of preventing corrosion-related problems. However, such reinforcing bodies can only be used to a limited extent in certain environmental conditions, for example where chlorine is present in high concentrations. In addition, they involve very high costs, which has hitherto opposed any comprehensive use.

Furthermore, there are also detrimental impacts on the environment. Since the aforementioned corrosion-protected reinforcing bodies are too expensive, it is recommended that concrete be applied with a thickness of between 75 mm and 120 mm to conventional steel reinforcements in order to cover the steel reinforcing struts sufficiently and in this way to try and prevent them from corroding. Non-renewable natural resources are severely stressed due to the large amount of concrete involved. In addition, unnecessarily large amounts of CO₂ are emitted due to the increased production of cement.

For this reason, the use of reinforcing bodies made of fiber-reinforced plastic, also referred to internationally as “FRP-rebars” (“FRP” being short for “fiber reinforced plastic”), is proposed as a substitute for corrodible steel reinforcements. Such FRP reinforcing bodies are resistant to corrosion and relatively inexpensive, so the aforementioned problems with corrosion can be combated permanently and efficaciously at low cost.

Fiber-reinforced plastics are composite fiber materials in which the plastic is combined with fibers made of a different material in order to obtain synergy effects and properties that are improved in the desired direction, especially to obtain mechanically improved properties. The fibers used can be glass fibers, for example, which are preferably embedded in the plastic with “unidirectional” fiber orientation in the longitudinal direction of a rod profile. A plurality of fibers aligned parallel to one another and which can have a diameter of between 10 and 30 μm, for example, is thus surrounded by a matrix of plastic resin. The fibers give the composite material its high strength in the longitudinal direction, while the resin matrix serves to fix the fibers in position and simultaneously to protect them against damaging influences.

In addition to individual reinforcing rods, reinforcing bodies of the kind initially specified and made of fiber-reinforced plastics, in particular, are also known. The connecting agents used to connect the individual plastic rods to one another are often wires, however, particularly conventional tying wires, which in turn are prone to corrosion and can lead to the aforementioned problems. In addition, these wire connections are only a temporary form of securing during transport and assembly, whereas after the concrete has hardened they can no longer make any significant contribution to increasing the tensile and shearing forces of the concrete body. Such reinforcing bodies comprising reinforcing rods connected by wires are known, for example, from document WO 01/26974 A2.

Cable ties made of plastic, known from the field of electrical installation, are also used for connecting the individual rods. By this means, however, as with the use of wire, only an extremely limited strength can be achieved, and the individual reinforcing rods are still always moved relatively easily in relation to one another. These connecting agents merely result, likewise, in reinforcing bodies which do not optimally increase the load-bearing capacity of the concrete body.

It is also known to intermesh single reinforcing rods made of fiber-reinforced plastic, but this involves considerable production complexity and correspondingly high costs. In the case of intermeshing, it is also necessary to deform at least individual reinforcing rods, with the result that this type of connection cannot be used in the case of fully hardened reinforcing rods.

A planar lattice fabric of the kind initially specified, and which can also be used as a reinforcing body, is known from document EP 0 387 968 A1 and from the associated German document DE 690 02 071 T2, in which the connecting agents comprise a warp yarn that is woven as a connection fiber into a plastic matrix. However, the connection fibers in this leno fabric, with a very small weft bending index of maximum 0.03, are curved to only a very small extent, with the result that they run almost in a straight line, substantially parallel to a reinforcing rod, and at the connecting points contact the transversely running reinforcing rods merely from one side over a highly limited circumferential portion. This type of interweaving or intermeshing can only result, therefore, in a reinforcing body which has only relatively low strength and which is thus unable to provide optimal support for a concrete building.

The object of the present invention is therefore to provide a reinforcing body of the kind initially specified and of simple design, in which the individual reinforcing rods are joined together in a simple and efficient manner such that a very high strength is achieved while simultaneously enabling inexpensive production.

This object is achieved according to the invention by a reinforcing body according to claim 1. Advantageous configurations and developments of the invention are derived from the dependent claims.

An important aspect of the inventive solution is that the connection fibers embedded in a plastic matrix are wound several times about the reinforcing rods at the connecting points.

The main advantage lies in the fact that, in a surprisingly simple manner, a high-strength, in particular undisplacable and positionally stable connection of the individual reinforcing rods to one another is obtained, which can be produced with relatively little production effort and therefore at low cost. The reinforcing rods are connected to one another in a particularly strong manner at the connecting points by multiple winding and subsequent hardening, such that a high-strength reinforcing body is obtained that ensures an optimal increase in the mechanical stability of a concrete structure provided therewith. At each individual connecting point, extremely high connecting forces are achieved.

Complex intermeshing or interweaving of the individual reinforcing rods is not necessary for this purpose, so the reinforcing rods do not need to be deformed, and even fully hardened reinforcing rods can be joined to one another relatively simply and quickly.

By embedding the connection fibers in a plastic matrix, the reinforcing rods are connected to one another substantially more strongly than is possible when using cable ties or wires. The connecting agents used according to the invention are formed for their part by fiber-reinforced plastic, which can have connection fibers of any kind, any length, any diameter and any arrangement.

No corrodible connecting agents are used here, so flaking of concrete due to corrosion, as well as cracks, damage and destruction of concrete buildings can be reliably prevented, while the weight of the reinforcing bodies is very low in total. This results in substantial savings in respect of maintenance and repair work. It is also possible in this way to relieve stress on natural resources, since concrete can be applied substantially more thinly and in significantly smaller volumes to the structures provided with the inventive reinforcements.

It is particularly advantageous with the inventive reinforcing body when the connection fibers are wound in different directions and/or with different orientations about each connecting point. The connection fibers are preferably wound about the intersection at a cross-shaped connecting point at an angle of 45° to the left and at an angle of 45° to the right. This enables a particularly stable connection to be obtained.

According to one preferred embodiment of the invention, the connection fibers each intersect at a connecting point at one point or at two points on one reinforcing rod or on both reinforcing rods, respectively. By means of this type of winding, the strength of the connection can be further increased. Nevertheless, it is equally possible to wind the fibers about the reinforcing rods at the connecting points in such a way that winding about the two reinforcing rods is done without criss-crossing and in a U-shape.

Furthermore it is particularly advantageous when the connection fibers are wound about the reinforcing rods in such a way that, when a tensile stress or compressive stress acts transversally to the longitudinal axis of a first reinforcing rod in the longitudinal direction of a second reinforcing rod, a connecting force S which satisfies the equation S>0.3*A_S*R_B is reached for a single connection point, where A_S is the cross-sectional area of the second reinforcing rod and R_B is the permissible working stress of the second reinforcing rod. In this way, especially when the connections are implemented with textile glass as the connection fiber and epoxy resin as the matrix resin, connecting forces of up to 5000 N can be achieved at a single connecting point with reinforcing rods having a diameter of 6 mm. Such high-strength yet highly compact connections between the reinforcing rods thus fulfill the same requirements as welding together reinforcing bodies made of steel.

It is particularly advantageous with the inventive reinforcing body when the connection fibers include glass fibers and/or aramide fibers and/or carbon fibers. However, it is also possible to use other fibers, for example silicon carbide fibers or boron fibers. The connection fibers preferably comprise only one and the same kind of fiber.

It is also favorable when the connection fibers and/or the plastic in the plastic matrix at the connecting points consist of the same material as the fibers or plastic in the reinforcing rods. By this means, the production effort involved can be kept particularly low.