EP0184995A2 - Reinforcement system preventing shearing - Google Patents

Abstract

Until now, areas of flat roofs (2) which are liable to get perforated, for example near a support (1), have required an extremely complex reinforcement of crosswise-arranged layers of reinforcement bars at the top and at the bottom, connected by innumerable shear ties which have to be positioned individually. The new shear reinforcement system, however, uses a shear basket element (3) which connects the required shear ties by means of connecting rods to form an integral component extending across the endangered area, is placed on the bottom reinforcement layer (5) and extends from the bottom reinforcement (4, 5) up to the top reinforcement (4', 5'), the internal layer (4') of which can be readily inserted into the hook shaped ends of the shear ties which are aligned with each other. This means they do not need to be inserted from the longitudinal side, and the height of the shear ties combined in the shear basket element (3) ensures the statically correct position of the top reinforcement (4', 5'), without a spacer element being required therefor. This results overall in substantial savings in labour hours. <IMAGE>

Description

The invention relates to a shear reinforcement system to ensure the load-bearing capacity of zones of reinforced concrete plates that are subject to shear forces, in particular zones of flat slabs that are at risk of punching, each with a lower and upper reinforcement included therein, running parallel to the flat slab and comprising at least one reinforcement layer.

A common example of such a reinforced concrete slab is the flat ceiling above an extensive underground parking space for commercial vehicles, on which there is a parking lot, and which rests all around on walls, but between them on a support or the majority thereof. On the circumference along the walls, a shear load acts on the ceiling, but a much larger one on the much smaller circumference of a column. In the area of the column cross section, an upward transverse force acts on the ceiling, but immediately outside this area there is a downward force of the same amount from the weight of the ceiling and its load, i.e. along the circumference of the column, the ceiling is severely sheared and in the surrounding zone Bend claims what is known to be a very unfavorable type of stress in concrete. This creates the danger that the ceiling will be punched through there.

In order to rule this out, zones of reinforced concrete slabs, e.g. Flat ceilings, provided with an extremely complex and dense steel reinforcement, e.g. consisting of lower and upper reinforcement layers crossing one another in the longitudinal and transverse directions, connected by countless individual so-called push bars, the placement and fastening of which is extremely critical, and when assembling you usually have to do spacing -Devices to help and you can at least partially the reinforcement bars just insert lengthways. You need trained and knowledgeable, conscientiously working specialists, a precise control of all details by the structural engineer is impossible, and so the production of such a reinforcement on the construction site is extremely time-consuming and expensive, while the risk of errors cannot be completely ruled out.

• a] Wenigstens in der am meisten beanspruchten und gefährdeten Zone ist ein Schubkorbelement, das sich aus der unteren bis in die obere Bewehrung erstreckt, oder eine Kombination aus mehreren solchen Schubkorbelementen angeordnet;
• b] das Schubkorbelement besteht aus U-förmigen Schubbügeln, deren in Querkraftrichtung, bei horizontalen Flachdecken somit nach oben weisende Schenkel an ihren Enden hakenartig abgebogen sind, und aus Verbindungsstäben, die mit den sie kreuzenden Schubbügeln an den Kreuzungsstellen fest verbunden sind;
• c] hierbei ist die Form und die gegenseitige Lage der Schubbügel und der Verbindungsstäbe so gewählt, daß das Schubkorbelement ein zusammenhängendes Ganzes bildet;
• d] das Schubkorbelement liegt unmittelbar auf der untersten Bewehrungslage, während die Stäbe der oberen Bewehrung, welche das Schubkorbelement quer zu den hakenartig abgebogenen Schubbügelenden kreuzen, in die jeweils in der Flucht der Stäbe liegenden Schubbügelenden eingelegt sind;
• e] demgemäß ist die Höhe der Schubbügel gewählt, so daß die statisch richtige Lage der oberen Bewehrung schon ohne Verlegen einer Distanzhaltevorrichtung für die obere Bewehrung gegenüber der unteren Schalung gewährleistet ist.

The invention remedies this by being based on the idea of a push reinforcement system which, instead of individual push bars, contains a prefabricated, therefore inexpensive and mass-produced push-pull element or its plurality, and which eliminates special spacing measures, longitudinal insertion and other complications. The new shear reinforcement system is characterized by the following features:

• a] At least in the most stressed and vulnerable zone there is a drawer element that extends from the lower to the upper reinforcement, or a combination of several such drawer elements;
• b] the push cage element consists of U-shaped push bars, the legs of which, in the transverse direction, with horizontal flat ceilings thus pointing upward at their ends, are bent like hooks, and of connecting rods which are fixed at the crossing points with the push bars crossing them are connected;
• c] Here, the shape and the mutual position of the push bracket and the connecting rods is chosen so that the push basket element forms a coherent whole;
• d] the push cage element lies directly on the lowest reinforcement layer, while the bars of the upper reinforcement, which cross the push cage element transversely to the hook-like bent thrust bar ends, are inserted into the push bar ends which are in alignment with the bars;
• e] accordingly, the height of the push bracket is selected so that the statically correct position of the upper reinforcement is guaranteed even without laying a spacer device for the upper reinforcement relative to the lower formwork.

Usually, two reinforcement layers from the known reinforcing bars crossing each other in the longitudinal and transverse directions are provided as the lower and upper reinforcement. Then you simply place the new drawer element on the lowest reinforcement layer - e.g. such that its connecting rods stand on the rods of this reinforcement layer, while the push bars reach into them, provided that the connecting rods run above the push bar webs; it is then advantageous to insert the second, the lowest crossing position of the lower reinforcement in the area of the push cage element in its push bracket. With the bars of the lower layer of the upper reinforcement, there is no need to push them in; they are then only to be inserted and fastened in the hook-like bent ends of the push handle, easily separated from the push element, other arrangement errors are also prevented, and finally the top reinforcement layer is placed, also without further ado arranged correctly. Thanks to the invention, significant progress is thus achieved with simplification and cost-effectiveness.

Some embodiments of the new push reinforcement system have the common feature that the connecting rods directly above and / or under the webs of the push bar in a mutual distance parallel to each other, which is smaller than the push bar width, and that the push bars are perpendicular to the connecting rods and along these, at least insofar as it is not the outer on both sides, so alternately laterally offset that they are at least two each Cross connecting rods and, thanks to the arrangement and firm connection at the intersection points, bring about a firm connection of all connecting rods with one another, so that the drawer element as a whole forms a coherent whole.

In one of these embodiments, the push bars in the direction of the connecting rods are at least approximately evenly spaced in rows and they are laterally offset along one of the connecting rods in such a way that they alternate between this and the adjacent connecting rod on the left, this and the adjacent connecting rod on the right, and the two left and right adjacent connecting rods, but then do not cross the relevant connecting rod itself and are firmly connected to it.

Three variants of this are important. To save material, at least some of the connecting rods can be interrupted where push bars cross the two connecting rods on the left and right, but not the connecting rod in question.

Another two of these variants deal with the possibility of being able to place adjacent push basket elements in such a way that the overall structure remains uniform. One of these variants is that the push handles have the same width and that only those crossing the outer connecting rod are those , pushrods firmly connected to it are provided, which cross this and the next inner connecting rod, while the other outer connecting rod is completely equipped with crossing pushrods that are firmly connected to it, as if there was another connecting rod outside of it. In this way you can have two such drawer elements easily connect to each other without additional parts by using. which, for example, is welded from one drawer element to the other overlapping push bracket with the latter connecting rods. The other of these variants maintains the uniformity of the structure when assembling two or more push cage elements in that push bars of full width are alternately provided at least along one outer connecting bar, which push bars cross the outer and the next inner connecting bar and are firmly connected thereto, and push bars of less , eg half width, which only cross the outer connecting rod and are firmly connected to it.

Another embodiment with the aforementioned common feature is designed so that the distance from push bar to push bar in the direction of the connecting rods is alternately equal to a constant value and zero, and that in the latter case the two adjoining push bars 33 forming a pair of push bars are laterally offset from each other that one leg of one is in the middle between the legs of the other. In this case, equal distances between the push arm legs in the longitudinal direction and in the transverse direction are made possible, which will be discussed in more detail below.

The latter possibility also exists in another, advantageous embodiment in that longitudinal connecting rods and cross connecting rods are provided as connecting rods, each of which runs parallel to one another at a distance from rod to rod approximately equal to twice the push bar width, cross each other at right angles and at their crossing points are firmly connected to each other, and that push bars are arranged transversely to each longitudinal connecting rod, which they cross in the middle of their web, where they are firmly connected to it. It is then expedient to arrange the push bars on the longitudinal connecting rods approximately in the middle between the transverse connecting rods. So this is a very regular arrangement: the individual push bars are aligned with each other in the longitudinal and transverse directions. They do not have to connect connecting rods, but the cross-connecting rods serve this purpose separately,

A variant of this is that longitudinal and transverse connecting rods are provided as connecting rods, each of which is at a distance from rod to rod equal to the push bar width, cross each other at right angles and is firmly connected to one another at their crossing points, and that the push bar is transverse stand on two adjacent longitudinal connecting rods and cross them at the lower end of their legs, where they are firmly connected to them. The smaller distances between the connecting rods compared to the previous one, as well as the additional connection of two rods by the push bar, naturally lead to greater stability of the entire push basket element; The first step here is to attach the push bars as regularly as in the previous arrangement, i.e. such that they are aligned with each other in the longitudinal and transverse directions, and the thrust arm legs can also be given equal distances in both directions.

In this variant, you can also restrict yourself to providing only the legs of the push bars; however, these should then be solidly connected to the longitudinal or transverse connecting rods or to their crossing points, not simply tacked. A connection at the crossing points can be e.g. Manufacture by using a pipe fitting consisting of three mutually perpendicular pieces of pipe and inserting the longitudinal and transverse connecting rod as well as the push bracket leg in order to glue them, e.g. with an epoxy resin with hardener or with a cyanoacrylate.

However, one can instead arrange the push bars laterally offset, so that they alternately connect this along a longitudinal connecting rod with the one on the left and the one on the right. Then the cross-connecting rods can also be omitted.

Generally it is advantageous if the ends of the legs the push bars are hook-like bent by at least approximately 180 ° in such a way that bars of the upper reinforcement can be inserted into the hook-like bends, and that the push bars are aligned for the same purpose so that the hook-like bends are aligned with one another in rows.

In some of the described embodiments, it was mentioned that the legs of the push bars can each have the same distances from one another in the longitudinal direction and in the transverse direction. The arm leg density is then isotropic. This is advantageous if the transverse force is approximately the same in both directions or approximately constant around the support. Another advantage is that with large transverse forces you can choose correspondingly small stirrup leg distances without necessarily having to accept smaller ones in one direction, which results in a corresponding saving in material. However, the other embodiments with a fundamentally anisotropic stirrup leg density are in place when transverse forces of different magnitudes are specified in the longitudinal and transverse directions; of course such drawer elements must then be correctly arranged on the construction site - not rotated by 90 °, i.e. then they are not easily foolproof.

In special applications it can be advantageous if the connecting rods or the longitudinal connecting rods and / or the transverse connecting rods have a smaller mutual distance in the area of the edges of the drawer element than in the middle, and / or that transverse connecting rods are only provided in the relevant edge areas in addition to the longitudinal connecting rods . One can then speak of stabilizing or stiffening bars in the edge area, which make the entire drawer element in particular more resistant to warping.

The described embodiments suggest others to those skilled in the art, including those where the drawer element is not, as is most often used, rectangular or in plan is square, but has such a shape that it can be inscribed in a parallelogram, circle or circle sector. The connecting rods can run parallel to two mutually opposite parallelogram sides or be arranged radially.

Finally, the material from which the drawer element is made is worth mentioning, because it plays a crucial role in the strength and durability of a building in places of high stress. _{E At} least in the long term, the durability is not a decisive factor or, in the opinion of the owner, besides irrelevant of the costs, the drawer element can consist of ordinary reinforcing steel in the way that has long been common for reinforcement parts.

Now, in addition to the better-known "forest dieback", there is of course an analogous phenomenon, namely that of the same cause, air pollution, which could be called "concrete dieback". Sulfur dioxide and nitrogen oxides form with the moisture that is always present in the air, but also contained in the concrete, which penetrate the by far not diffusion-proof concrete over time, thereby reaching the reinforcement and corroding it, which increases the volume of the reinforcing bars and they finally blow up the surrounding concrete. Given the particularly high reinforcement density with push bars, etc. in the area of the zones of reinforced concrete slabs that are at risk of punching, the risk of the concrete exploding is particularly high there or is to be expected all the sooner.

A thicker concrete cover and a higher cement content of the concrete have been proposed to remedy this, but this can only delay the damage somewhat, because those pollutants eventually penetrate a thicker porous layer, and their higher alkali content is finally also due to the constant exposure to the acidic pollutants neutralized. Contrary to widespread opinion, the galvanizing of the reinforcement parts that has already been proposed is not resistant to these pollutants and can therefore only delay the damage slightly.

In order to prevent this corrosion permanently, the inventor suggests that the drawer element be made of smooth or at least partially profiled round steel, which is coated with a corrosion-resistant and diffusion-tight plastic, or of stainless steel. The suitability of the latter is beyond question and the higher costs are disproportionate to the damage it prevents. Certain acids, to a certain extent, are attacked by certain acids if they are very dilute and therefore have a high degree of dissociation, but this is only manifested by a surface discoloration, which is not accompanied by a noticeable increase in volume.

For the plastic coating is not a solvent-based paint or the like. into consideration, because after the solvent has evaporated, the layer would not be diffusion-tight. Usual two-component resin-hardener mixtures become very hard when hardening with shrinkage, coatings from them therefore become cracked and therefore useless. If you add a plasticizer to them, they are then not diffusion-proof and therefore also useless for the present purpose. The proposal therefore initially relates to the use of bisphenol-A-epichlorohydrin as a resin and a tertiary amine from very long chain molecules as a hardener, e.g. Cocosamine; after curing, this is sufficiently elastic even without a plasticizer, so that it does not form any cracks as a coating, and is perfectly diffusion-tight even against the smallest molecules, and it is also one of the few plastics that are permanently resistant to those pollutants. However, this does not exclude that other plastics with properties suitable for the present purpose are found.

It is obvious that both measures, the use of stainless steel for this special task and especially the plastic coating, would not be practical on the construction site. This is the advantage of the invention not to be underestimated that thanks to the prefabrication of the drawer element - that is to say for the area most at risk from that concrete blasting - it easily offers the possibility of taking one or the other of these measures,

The accompanying drawings illustrate the invention using some exemplary embodiments.

Fig.1 shows on a support 1, which is indicated with a bold square, a section of a flat slab 2, while the new shear reinforcement system in it hinted at with four composite drawer elements 3 or a correspondingly larger, and with longitudinally extending lower and upper reinforcement layers 4, 4 'and transverse and lower and upper reinforcement layers 5, 5 ". If FIG. 1 is viewed as a view from above, FIG. 2 is the section through the support 1 of the same arrangement seen from the lower edge of the sheet The representation of the drawer element 3 in FIG. 2 could only correspond to a specific embodiment - the one from FIGS. 9 to 11 was chosen - but is not to be understood in particular why here also all parts of the drawer element, generally meant according to the invention, are denoted uniformly by 3.

A first embodiment of the drawer element is shown in Figures 3 to 5; in Figure 3 in top view, in Figure 4 in side view from the direction in Figure 3 below, in Figure 5 for illustration in perspective. The mutual distance from connecting rods 32 is smaller than the width of push bars 30, each of which is firmly connected to the two connecting bars 32 crossing it, while narrower push bars 31 at the edge ensure a more uniform finish.

6 to 8 represent a second embodiment of the push cage element in the same arrangement and manner of representation. Here, too, the mutual spacing of connecting rods 35 is smaller than the width of push bars 33 crossing them, each of which crosses two connecting rods and is firmly connected thereto; the mutual distance of the push bars 33 in the direction of the connecting rods 35 is, however, alternately equal to a constant value and equal to zero, while the legs of the push bars in this direction and transversely to them have the same distances. At the edge, narrower push brackets 34 ensure a uniform closure and the connecting rods 35 are provided at a smaller distance and cross-connecting rods 36 for stiffening the push basket element.

9 to 11 represent a third embodiment of the drawer element, in which push brackets 37 are fastened on longitudinal connecting rods 38 crossing them, which in turn are connected and held together by cross-connecting rods 39. Here too, as shown, the distances between the push handle legs can be kept the same lengthways and crossways.

Claims (16)

1. Shear reinforcement system to ensure the load-bearing capacity of zones of reinforced concrete slabs that are subject to shear forces, in particular zones of flat slabs that are at risk of punching, each with an enclosed lower and upper reinforcement running parallel to the flat slab from at least one reinforcement layer,
characterized by the following features: a] At least in the most stressed and vulnerable zone is a push bar element [3], which extends from the lower reinforcement [4, 5] to the upper reinforcement [4 ', 5'], or a combination of several such push bar elements arranged; b] the push cage element [3] consists of U-shaped push bars [30, 31, 33, 34, 37], the legs of which, in the transverse direction, in the case of horizontal flat ceilings [2], are bent at their ends like hooks, and from connecting rods [32, 35, 38; 36, 39], which are firmly connected to the push bars crossing them at the crossing points; c] here is the shape and the mutual position of the Push bracket [30, 31, 33, 34, 37] and the connecting rods [32, 35, 38; 36, 39] selected so that the drawer element [3] forms a coherent whole; d] the push cage element [3] lies directly on the lowest reinforcement layer [5], while the bars [4 '] of the upper reinforcement, which cross the push cage element transversely to the hook-like bent thrust bar ends, are inserted into the push bar ends that are in line with the bars are. e] accordingly, the height of the push bracket [30, 31, 33, 34, 37] is selected so that the statically correct position of the upper reinforcement [4 ', 5'] is already without laying a spacer for the upper reinforcement relative to the lower formwork is guaranteed. 2. push reinforcement system according to claim 1, characterized in that the connecting rods [32, 35] directly above and / or below the webs of the push bracket [30, 33, 34] at a mutual distance from each other ₃ which is smaller than the push bar width, and that the push bars are perpendicular to the connecting rods and along these, at least insofar as it is not the outer one on both sides, are alternately laterally offset in such a way that they cross at least two connecting rods and, thanks to the arrangement and fixed connection, a fixed one at the crossing points Connect all the connecting rods together so that the drawer element [30-32, 33-35] is a coherent overall Whole forms. 3. shear reinforcement system according to claim 2, characterized in that the push bracket [30, 31] in the direction of the connecting rods [32] have rows at least approximately uniform distances and along one of the connecting rods are arranged laterally offset such that they alternately this and the one on the left Connecting rod, this and the adjacent connecting rod on the right, and the two adjacent connecting rods on the left and right, but then do not cross the connecting rod itself and are firmly connected to it. 4. shear reinforcement system according to claim 3, characterized in that at least part of the connecting rods [32] is interrupted where push bars [30) cross the two left and right adjacent connecting rods, but not the connecting rod in question. 5. thrust reinforcement system according to claim 3, characterized in that the push bars [30, 31] have the same width, and that along the one outer connecting rod [32] only those crossing it, firmly connected to him push bar are provided, which this and the next interior Cross the connecting rod, while the other outer connecting rod is completely equipped with push bars that cross it and are firmly connected to it, as if there was another connecting rod outside of it. 6. shear reinforcement system according to claim 3, characterized in that at least along one of the outer connecting sta bes [32] alternately full width push bars [30] are provided, which cross the outer and the next inner connecting rod and are firmly connected thereto, and push bars [31] of smaller width, which only cross the outer connecting rod and are firmly connected thereto. 7. push reinforcement system according to claim 2, characterized in that the distance from push bar to push bar [33] in the direction of the connecting rods [35] is alternately equal to a constant value and equal to zero, and that in the latter case the two adjacent push bars forming a push bar pair [33] are laterally offset from one another in such a way that one leg of one is in the middle between the legs of the other. 8. shear reinforcement system according to claim 1, characterized in that as connecting rods longitudinal connecting rods [38] and cross-connecting rods [39] are provided, each running parallel to each other at a distance from rod to rod equal to twice the push handle width, cross each other at right angles and on their crossing points are firmly connected and that transversely to each longitudinal connecting rod [38] push bar [37] are arranged, which they cross in the middle of their web, where they are firmly connected to it. 9. shear reinforcement system according to claim 1, characterized in that longitudinal and transverse connecting rods are provided as connecting rods, each at a distance run parallel to each other from bar to bar equal to the push bar width, cross each other at right angles and are firmly connected to each other at their crossing points, and that the push bars stand transversely on two adjacent longitudinal connecting bars and cross them at the lower end of their legs, where they are firmly connected to them are. 10. Thrust reinforcement system according to claim 9, characterized in that instead of the push bracket only the legs are provided. 11. Thrust reinforcement system according to claim 9, characterized in that the cross-connecting rods are omitted, and that the thrust element thereby forms a coherent whole that the push bracket relative to the longitudinal connecting rods are arranged laterally offset such that they each alternate with the left and with the connect right neighboring. 12. Thrust reinforcement system according to one of the preceding claims, characterized in that the ends of the legs of the push bracket [30, 31, 33, 34, 37] are bent like a hook by at least approximately 180 ° such that bars [4 '] of the upper reinforcement in the hook-like bends can be inserted, and that the push bars are aligned for the same purpose so that the hook-like bends are aligned with one another in rows. 13. shear reinforcement system according to one of claims 7 - 11, characterized in that the legs of the push bracket [33, 34, 37] in the longitudinal direction and in the transverse direction each have the same distances from one another. 14. Thrust reinforcement system according to one of the preceding claims, characterized in that the connecting rods [32, 35] or the longitudinal connecting rods [35] and / or the transverse connecting rods [36] have a smaller mutual distance in the region of the edges of the push cage element than in the middle, and / or that cross connecting rods [36] are only provided in the edge area in addition to the longitudinal connecting rods [35]. 15. shear reinforcement system according to claim 1, characterized in that the drawer element [3] has such a shape in plan that it is inscribable a rectangle, square, parallelogram, circle or circle sector, and that the connecting rods parallel two opposing rectangles, squares - or parallelogram sides run or are arranged radially. 16. shear reinforcement system according to claim 1, characterized in that the thrust element [3, 30 - 39] made of smooth or at least partially profiled round steel, which is coated with a corrosion-resistant and diffusion-tight plastic, or consists of stainless steel.

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