DE1251505B - - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

Int. Cl .:

GERMAN

PATENT OFFICE

EDITORIAL

German class: 37 b-3/26

Number: 1 251505

File number: A 28042 V / 37 b Filing date: October 7, 1957 Open date: October 5, 1967

The invention relates to a beam, in particular to one made of concrete reinforcements prestressed in tension and compression. For reinforced concrete structures with slack reinforcement, it is known to increase the load-bearing capacity by inserting slack pressure reinforcement made of steel or the like. Due to the bond between steel and concrete, however, the permissible stress on the pressure reinforcement cannot be exploited. The stress remains rather because of the limited by the bond with the concrete of the pressure zone Compression compression far below the stress permissible for steel. By prestressing the tensile reinforcement, by generally loading the concrete cross-section under pressure and a bending counteracting the constant load, the Relieve the concrete pressure zone, so that, in addition to other advantages, the load-bearing capacity of such a cross-section is also reduced by relieving the pressure zones is increased with prestressed tensile reinforcement. A further reinforcement of the concrete pressure zone takes place here again by inserting slack reinforcement. However, with such tensile prestressed reinforcing bars, it is only possible to generate either pressure alone or pressure with bending in the concrete cross-section. For structures that are stressed purely on bending by the external loads, the portion of the preload that is only generates centric pressure, an undesirable side effect, as it may put too much pressure on the cross-section. There are therefore There are certain limits to the use of tensile prestressed reinforcement.

In the production of concrete girders provided with pre-stressed reinforcement, it has already been proposed that they also be pre-stressed under pressure Provide reinforcement. However, since they were arranged in the prestressing bed, these compression reinforcements were where they were only surrounded by concrete after their prestressing. It had to Therefore, for these reinforcements, complicated cross-sections are chosen without excessive Cost of materials to achieve at least a certain buckling resistance, and it was not possible that To actually use the compressive strength of such reinforcements. It was suggested here, to reduce the buckling lengths by providing cross brackets, however, are sufficient Such cross brackets are also not used to prevent buckling. Such prestressed Pressure reinforcements could not prove themselves.

The invention now aims to produce a beam,

Beams, especially made of concrete, with prestressed reinforcement

Applicant:

Dipl.-Ing. Dr. Hans Reiffenstuhl, Baden, Vienna (Austria)

Representative:

Dipl.-Ing. F. Weickmann, Dr.-Ing. A. Weickmann, Dipl.-Ing. H. Weickmann

and Dipl.-Phys. Dr. K. Fincke, patent attorneys,

Munich 27, Möhlstr. 22nd Named as inventor:

Dipl.-Ing. Dr. Hans Reiffenstuhl, Baden, Vienna (Austria)

in particular to create concrete, with reinforcement prestressed under tension and compression, and consists essentially in the fact that the pressure prestressed reinforcement in tight, preformed, ge closed or open channels of the structure whose walls absorb the reaction forces of the compression reinforcement. These channels can if necessary, subsequently filled with concrete, mortar etc. or with plastic material the, as is the case with tensile prestressed reinforcement gen is known per se. When using concrete, mortar or the like, a subsequent composite is produced, and it is the production of this composite also by other known means, such as wisely by clamping action, upsetting, screwing ben thread etc. possible. Concrete beams with reinforcements prestressed under pressure are known, but the latter are not located in the channels of the finished ones Beams but are in a bed on top Pressure pre-stressed and then embedded in the concrete. After the concrete has hardened, the Pressing released, whereby the compressive force of the reinforcement is introduced into the beam through adhesion. Because of the high levels required for this process Rigidity of the profiles should have a large moment of inertia with a small cross section. the Anchoring through adhesion requires a great deal

709 650/89

Surface, therefore the profiles should be open and additionally roughened on the surface or with unevenness be equipped.

It is also already known to provide an element in a concrete beam, which in a Channel is temporarily biased for the purpose of pressure to an outside of the pipe Tensile reinforcement after stressing with a press until the concrete is embedded and hardened, i.e. until the adhesive connection between the tensile reinforcement and the concrete is established, in the tensioned state To keep state. The only task of the pipe is to keep the concrete away from the temporary compressive stress member. The outside around the pipe The tensile reinforcement located inside the pipe is essential to prevent the kinking of the inside of the pipe located pressure member. The main difference compared to the subject of the invention, however, is in that the pressure member does not remain in the concrete beam, but after the concrete has hardened and manufactured the adhesive connection between this and the tensile reinforcement released by the latter and pulled out whereas the subject of the invention is a compression tendon that remains permanently in the concrete beam acts.

The pressure prestressed reinforcements according to the invention can be formed from bars, which have a not significantly increased moment of inertia compared to the circular cross-section. You can z. B. have the same cross-section as the tensile prestressed reinforcing bars and also from consist of the same material as this, whereby the work and storage are simplified. As a result of the fact that buckling occurs through the walls of the channels in which these pressure reinforcements are laid the same is limited, is no longer the load capacity of these pressure reinforcements Buckling strength, but actually the compressive strength decisive, so that the compression reinforcements in can be prestressed to the same extent as the tensile reinforcement. It can through it a significant reduction in the concrete cross-section in the pressure zone and its own weight of the structure can be reduced, which again increases the load capacity due to the payload will. In this way, new possibilities in reinforced concrete construction are created, and it becomes for example makes it possible to achieve greater spans than before with smaller construction heights of the supporting structures. In the borderline case, a combination of prestressed tension and compression reinforcement is a state can be produced, in which only pure bending arises from the compressive and tensile prestress. - Is expedient at least some of the compression and tension prestressed reinforcement at the ends in one common clamping head merged. The number of merged in the clamping head on Compression prestressed and tensile prestressed reinforcement and / or the prestressing of the same is preferably chosen so that the tensile and compressive forces in the main direction at least approximately keep your balance. In this way, the end anchoring of the reinforcements is simplified, and the reinforcement can be subjected to both tensile stress and compressive stress with one stressing stroke be granted. If the reinforcing bars prestressed in tension and compression are not to completely keep your balance so just have to

the differential forces between the reinforcing bars prestressed in compression and tension from the girder or taken up by the guide of the anchoring body. The in anchoring in the common Spannhaupt normal to the main direction occurring side components of the pressure and Tensile forces can be absorbed by guides of the clamping head along support surfaces.

In the case of linearly guided, preloaded under pressure

ίο Reinforcements there is the possibility of limited buckling or deflection due to the play of the reinforcing bars in the channels receiving them. If necessary, the reinforcing bars prestressed in compression can be designed with a profile which makes buckling difficult, while simple round profiles can be used for the reinforcing bars prestressed in tension. According to a preferred embodiment of the invention, however, the on

so pressure prestressed rebars are laid in a curved position, so that they are at their convex Sides are supported on the concave surfaces of the channels. This way it becomes independent of the Size of the game of the reinforcing steel prestressed under pressure in the channels a support of the Reinforcing steel achieved, which prevents buckling or deflection of the same, so that it does not appear to be necessary to use kink-proof profiles.

The pressure reinforcement prestressed according to the invention can also be used in steel or light metal constructions, in particular the latter are used with success since they use high-strength materials with high loads and thus enables savings in building materials, without the structure suffering major changes in shape. The per se known use of prestressed tensile reinforcement in steel and light metal structures has not been particularly good up to now economical, as the portion of the tensile prestress that only generates centric pressure in the cross-section, often unnecessarily stresses the valuable material of the structure. This centric pressure in cross section is caused in part by the tensile pre-stressed reinforcement. When using However, this disadvantage can be reduced or eliminated by reinforcement prestressed under pressure. Included Pressure links in steel or light metal construction prevent buckling because of the plasticization of the building material decreases with the level of stress, for this reason there is often a greater cost of materials, as required due to strength. By concentrating the compressive force in pre-tensioned Pressure reinforcement made of high-quality material can be fully utilized on the one hand and on the other hand the surrounding material can be used for stabilization when it is less stressed.

In the drawing, the invention is illustrated schematically on the basis of exemplary embodiments.

F i g. 1 shows schematically a carrier;

F i g. 2, 3, 4, 5 and 6 show the voltage diagrams; F i g. Figure 7 shows a beam end with the clamping head; F i g. 8 and 9 show different ways of guiding the pressure-prestressed reinforcing bars in channels of the structure.

F i g. 1 shows a beam 1 on two supports 2 and 3. 4 represents a reinforcement bar known per se, prestressed in tension, while 5 represents one

Claims (6)

Pressure prestressed rebar shows. Of course, several such reinforcing bars 4 and 5 can be provided. In the cross-section in the middle of the beam, the diagrams in FIG. 2 to 6, where the sign + indicates the tensile stresses and the sign - indicates the compressive stresses. F i g. 2 shows the diagram of the stresses in the girder cross-section due to its own weight without taking the preload into account. These tensions are labeled Og. As a result of the tensile pre-tensioned reinforcement 4 arranged below, the one in the diagram according to FIG. 3, where ovz denotes the stresses generated by the tensile prestress. If the reinforcement 5 arranged above and prestressed under pressure is taken into account alone, the result in the diagram according to FIG. 4, the stresses generated by the compressive prestressing being denoted by ovd. If Og + ovz + OvlI = 0 at the upper and lower edge, which can be achieved by a suitable choice of the tie rods and the tension forces, the concrete actually remains tension-free under load. Since this borderline case would require a very uneconomical expenditure on prestressing steel, one will usually be content with a smaller compression reinforcement. F i g. 5 now shows, for example, a diagram in which the compressive stresses (-χ-) are half the size of the compressive stresses according to the diagram according to FIG. 4 have. An intermediate state is sought here, which is shown in the diagram according to FIG. 6 is shown, where ^ ο represents the sum of the voltages. F i g. 7 now shows an arrangement in which the reinforcement 5 which is prestressed under pressure and the reinforcement 4 which is prestressed under tension are brought together in a common clamping head 6. At the end of the beam 1 to be prestressed, a horizontal support surface 7 is provided which carries the clamping head 6, in which the tension reinforcement 4 is anchored with the compression reinforcement 5 in such a way that the vertical component of the two tension forces is transmitted via the support surface 7 into the support 2. The horizontal component of the two tension forces, on the other hand, is passed into the concrete body of the girder via a vertical support surface 8. Since, as a rule, the compressive tension force will be smaller than the tensile tension force, pressure is transmitted to the support surface 8, which, however, is considerably less than that which would have to be transmitted without compression tension reinforcement. According to the invention, the pressure reinforcement can now be laid in open or closed channels of the girder 1. F i g. 8 shows such a closed, rectilinearly guided channel 9 in which a movement rod 5 which is pretensioned under pressure is guided. Here there is within the channel 9 due to the play between the rod 5 and the walls of the channel 9, the possibility of a slight buckling or evasion, which is shown exaggerated in Fig. 8 in Brei th distortion. A round steel 5 is used here, but it can also be advantageous to use a shaped steel which has a significant moment of inertia. It could e.g. B. rolled sections are used, which can be advantageous due to their greater resistance to buckling. F i g. 9 shows an embodiment in which a reinforcing bar 5 prestressed under pressure is laid in a continuously curved channel 10. Under the effect of the compressive bias, this rod now rests consistently against the convex surface 11 of the channel so that it is supported against the convex surface 11 over its entire length. The support forces acting on the rod 5 are symbolically indicated by the arrows 12. These support forces now hold the rod 5 in a stable equilibrium position, so that buckling is no longer an option. The curvature of the channel 10 does not necessarily have to lie in one plane, but a spatial curvature can also be provided, the reinforcing bar 5 always resting on the concave side of the channel 10 under the effect of the compressive prestress. Patent claims: 1. Beams, in particular made of concrete, with reinforcement prestressed in tension and compression, characterized in that the pressure-pre-tensioned reinforcement in tight, pre-formed, closed or open channels of the beam, the walls of which the reaction forces the compression reinforcement. 2. Bar according to claim 1, characterized in that at least part of the pressure and the tensile prestressed reinforcement at the ends in a common tensioning head is merged. 3. Bar according to claim 1 or 2, characterized in that the cross section of the Reinforcement prestressed under pressure is not significantly increased compared to a circular cross-section Has moment of inertia. 4. Beam according to claim 1, 2 or 3, characterized in that the preloaded on pressure Reinforcing bars are laid in a curved position, so that they are attached to their convex side the concave surfaces of the channels are supported. 5. Bar according to one of claims 2 to 4, characterized in that the number of im Reinforcements brought together, prestressed under pressure and prestressed under tension and / or the biases thereof are chosen so that the tensile and compressive forces in the main direction are at least approximately keep your balance. 6. Beam according to claim 5, characterized in that the anchoring in one common clamping head normal to the main direction occurring side components of the pressure and tensile forces are absorbed by guides of the clamping head along support surfaces. Considered publications:
German Patent Nos. 832 670, 928 601;
U.S. Patent Nos. 1,967,827, 2,039,398. 1 sheet of drawings