Abstract:
A connecting device ( 1 ) for the shear-force connection of concrete components ( 20 ), in particular prefabricated concrete components, comprises: an elongate protective box ( 2 ) for fitting in an end face ( 20′ ) of the components ( 20 ), which comprises a bottom ( 5 ) and at least two side walls ( 6 ) extending in a longitudinal direction of the bottom; at least one flexible reinforcing loop element ( 3 ) which can be accommodated in the protective box ( 2 ) and can be moved out of the latter; characterized in that the bottom ( 5 ) has a bottom profiling with groups of bottom projections ( 7 ) and bottom depressions ( 7′ ) alternating in the longitudinal direction, wherein each group has at least one bottom projection ( 7 ) or at least one bottom depression ( 7′ ).

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a connecting device in accordance with the preamble of claim  1 . 
       PRIOR ART 
       [0002]    In order to erect load-bearing structures of a building constructed from precast concrete parts, the precast concrete parts have to be force-transmitting-connected with one another. Plate-shaped wall elements are connected to one another or to vertical columns at vertical joints. Corresponding casting channels are disposed at the end faces of the elements, on the base of which connecting elements with storage boxes are arranged, which contain reinforcing members that can be folded out. These reinforcing members can be made, for example, of concrete reinforcing bars. Such a so-called bend-back connection is disclosed, for example, in document DE 39 37 275 A1, however it has the disadvantage that the bending back of the concrete reinforcing bars is cumbersome and power-consuming and requires sturdy storage boxes with large dimensions. 
         [0003]    In a different concept, the reinforcing members can also be configured as flexible rope elements. Such storage boxes are disclosed, for example, in WO 03/008737, EP 0 914 531 A1 or EP 0 534 475 A1. By folding out these flexible rope elements, loop-shaped members are provided perpendicular to the end face, which overlap one another in the joint when the precast members are assembled. The loops which overlap one another in the joint are filled in the casting joint with casting mortar for the most part over the entire height of the precast members. Following hardening of the casting mortar, the casting joint is able, due to the overlapping connecting elements, to transmit forces in different directions, i.e. on the one hand to transmit tensile forces in the overlap perpendicular to the joint, i.e. perpendicular to the end face of the precast members, and on the other hand to transmit shear forces perpendicular to the plate plane and, particularly importantly, to transmit shear force parallel to the longitudinal direction of the joint. The latter represents a load case that occurs very frequently in construction practice. 
         [0004]    However, in contrast to the storage boxes with rigid reinforcing members (concrete reinforcing bars) as described above, the flexible rope elements only indirectly contribute to the transmission of shear forces since although they counteract an expansion of the connecting joint, they are, however, only able to develop small force components in the shear force direction owing to their flexibility. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the present invention to provide a connecting device of the type described above, which has at least one flexible reinforcing loop element and an improved shear load-bearing behaviour at the same time as a simple structure. 
         [0006]    This object is solved according to the present invention by a connecting device having the features of claim  1 . Advantageous further developments of the invention are specified in the dependent claims. 
         [0007]    The idea forming the basis for the invention is to improve the shear load-bearing behaviour by means of an optimised interlocking between the storage box of the connecting device and the surrounding concrete and to reduce the load of the wall component to the side of the storage box. For this purpose, it is provided according to the invention that the bottom of the storage box has bottom profiling with groups of bottom projections and bottom depressions alternating in the longitudinal direction, with each group having at least one bottom projection or at least one bottom depression. 
         [0008]    Owing to the alternating arrangement of the bottom projections and bottom depressions, a good overall interlocking results between the bottom of the storage box and the concrete, which can be achieved with comparatively little production effort, in particular comparatively low degrees of deformation when forming the bottom projections and bottom depressions. The good overall interlocking leads to it being possible to introduce shear force loads into the respective concrete part with little slip via the bottom of the storage box such that the force transmission via the connecting device can be activated before distinct crack formation occurs in the concrete. The shear force is furthermore introduced via the bottom of the storage box at a position in the concrete part at which it is no longer weakened by the joint. An often critical breaking-off of component flanks in the region of the joint is minimised in this manner. 
         [0009]    The design of the bottom of the storage box not least also acts favourably on the transmission of force within the joint itself, i.e. between the casting mortar, the flexible reinforcing loop elements and the storage box. The load-bearing behaviour in this area can be theoretically reproduced by a strut-and-tie model with tension ties and compression struts (even though the present invention is not restricted at all by this model). Shear forces parallel to the joint and the transmission thereof via the casting joint leads to compression struts that extend at an angle from the bottom of the storage box and side walls, which are supported on the respective opposite storage box. This support of the inclined compression struts that are important for the load-bearing behaviour is clearly improved by the design of the bottom of the storage box with alternating projections and depressions. At the same time, the flexible reinforcing loop elements ensure that the force component generated by the inclined compression struts, which tends to expand the joint, is accommodated and transmitted. 
         [0010]    As has been shown in extensive tests and analyses, an optimal combination of overall interlocking and/or shear load-bearing behaviour with simple producibility results if, according to a further development of the present invention, the bottom projections and bottom depressions each have a maximum height, with the total height of the bottom depressions and bottom projections of adjacent groups defining a total depth of interlock that is in the range of 3 to 9 mm, preferably 5.5 to 6.5 mm. It is thereby particularly preferred for the bottom projections and bottom depressions to have substantially the same height, i.e. for example, if the total depth of interlock is 6 mm, they each have a height of 3 mm. When producing the storage box, this results in a particularly low and uniform degree of deformation of the bottom depressions and projections, whilst a uniform load-bearing behaviour is at the same time established on both the inside and outside of the bottom of the storage box. This effect, as will be discussed in more detail below, is more pronounced the smaller the distance between the bottom projections and depressions. 
         [0011]    According to a further aim of the present invention, it is provided that the side walls of the storage box each have a wall profiling with groups of wall projections and wall depressions alternating in the longitudinal direction, with each group having at least one wall projection or at least one wall depression. The overall interlocking between the storage box and the casting mortar in the joint on the one hand and the concrete of the structural part on the other hand can be further improved in this manner, with an improved load-bearing behaviour resulting in particular in the case of a shear force load in the longitudinal direction of the elongated storage box. 
         [0012]    In the aforementioned tests and analyses, the inventors determined that a particularly advantageous combination of shear load-bearing capacity and simple producibility of the connecting device results if, in accordance with a further development of the present invention, the wall projections and wall depressions each have a maximum height, with the total height of the wall depressions and wall projections of adjacent groups defining a total depth of interlock that is in the range of 2 to 6 mm, preferably 3.5 to 4.5 mm. It is thereby particularly preferred also as regards the wall projections and depressions for these to have substantially the same height, i.e. for example, if the total depth of interlock is 4 mm, they each have a height of 2 mm, with the advantages discussed above. 
         [0013]    Aside from the fact that it is arranged in an alternating manner, the design of the bottom profiling and wall profiling is not particularly restricted within the scope of the present invention. However, it has proven to be advantageous for the load-bearing behaviour and producibility if the bottom profiling and/or wall profiling is designed in an undulated or serrated manner. Other forms of bottom profiling and/or wall profiling are also particularly preferred, which will be explained in more detail below with reference to the figures. 
         [0014]    In principle, the bottom projections and bottom depressions could also contribute within the scope of the present invention to the introduction of tensile forces into the respective concrete part. However, it has proven to be advantageous to assign the transmission of tensile forces primarily to the flexible reinforcing loop elements since these have a considerably greater anchorage depth in the respective concrete part and thus enable introduction of tensile forces at a high load-bearing capacity and low deformation. In view hereof, it is provided according to a further development of the present invention that the bottom projections and/or bottom depressions are configured in a trapezoidal manner and comprise flanks that are aligned substantially perpendicular to the bottom. In this manner, the bottom projections and bottom depression optimally contribute to the transmission of shear forces, however leave the transmission of tensile forces (perpendicular to the joint) largely to the flexible reinforcing loop elements. 
         [0015]    The same considerations also apply for the wall projections and wall depressions which, according to a further development of the present invention, have a lower anchoring resistance in concrete in a direction perpendicular to the bottom and thus to the joint than in a direction differing herefrom. In addition to the advantages already discussed above, this design also leads to an improved load-bearing behaviour in the region of the joint cast with mortar when a load is introduced into the concrete. Thus, in the strut-and-tie model discussed above, the component of a compression strut engaging in an inclined manner does not cause, perpendicular to the joint, any or only causes slight additional forces on the side walls of the storage box and thus on the component flanks in the region of the joint, it rather anchors itself primarily on the bottom of the box. At the same time, the shear force components acting parallel to the joint can continue to be effectively anchored at the side walls of the storage box, which benefits force transmission in this direction. 
         [0016]    It has proven to be advantageous within the framework of this concept for the wall projections and wall depressions to have an elongated form which extends substantially perpendicular to the bottom. The narrow side of this elongated form enables the desired low anchoring resistance perpendicular to the bottom, whilst the long side of the elongated form offers a beneficial support surface for the shear force components acting parallel to the joint. It is thereby particularly preferred that the elongated form of the wall projections and wall depressions tapers in the direction extending away from the bottom such that a correspondingly low anchoring resistance results in the direction extending away from the bottom. 
         [0017]    The groups of bottom projections and bottom depressions alternating in the longitudinal direction of the elongated storage box can, within the scope of the present invention, be at different distances to one another (also within an individual connecting device). However, according to a preferred embodiment of the present invention, it is provided that the bottom projections and bottom depressions and the wall projections and wall depressions of adjacent groups are separated by a narrow intermediate surface or directly follow one another. The narrower the respective intermediate surfaces, the better the adjacent groups of projections and depressions supplement one another to form a large total depth of interlock with correspondingly advantageous shear load-bearing behaviour. 
         [0018]    According to a further aim of the present invention, it is provided that the storage box is designed such that two opposite storage boxes of concrete parts that are connected with one another form as small a casting joint as possible, which is able to precisely accommodate the respective flexible reinforcing loop elements in the folded-out state, including a tolerance zone. A small joint volume and thus a reduced need for high-quality and expensive casting mortar is thereby achieved when connecting the concrete parts. This configuration also has a favourable effect on the shear load-bearing behaviour. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1   a  schematically shows a perspective view of a first embodiment of a connecting device according to the present invention; 
           [0020]      FIG. 1   b  schematically shows a perspective view of a storage box of a connecting device of a second embodiment of the present invention; 
           [0021]      FIG. 1   c  schematically shows a perspective view of a storage box of a connecting device of further embodiments of the present invention; 
           [0022]      FIG. 2   a  schematically shows a sectional view of a storage box of a connecting device according to further embodiments of the present invention; 
           [0023]      FIG. 2   b  schematically shows, as an example, different sectional views along the line A-A in  FIG. 2   a;    
           [0024]      FIG. 3  schematically shows a perspective view of a part connection using the connecting device according to the invention; 
           [0025]      FIG. 4  schematically shows a partial top view of the part connection as shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    Preferred embodiments of the present invention will be described in detail in the following with reference to the accompanying figures. 
         [0027]      FIG. 1   a  schematically shows a perspective view of a connecting device  1  as the first embodiment of the present invention. The connecting device  1  is used for the shear-force-transmitting connection of concrete parts, in particular precast concrete parts, which will be described in more detail below with reference to  FIGS. 3 and 4 . 
         [0028]    The connecting device  1  comprises an elongated storage box  2  that is made, for example, of sheet metal and is provided for being concreted into an end face of concrete parts. The storage box  2  has a bottom  5  and two side walls  6  that extend in the longitudinal direction of the bottom. The bottom has through-openings, through which a flexible reinforcing loop element  3  extends such that the loop section comes to rest in the region of the side walls  6 , whilst a clamping sleeve  3 ′ is respectively provided on the opposite side, which connects the free ends of the reinforcing loop element  3  with one another and contributes to improved anchorage in the concrete. The flexible reinforcing loop element can be, for example, a rope formed of wires or wire strands, with the reinforcing loop element, owing to its flexibility, being able to be accommodated in the storage box between the side walls  6  and moved out of the same.  FIG. 1   a  shows the flexible reinforcing loop elements  3  in the moved-out state. 
         [0029]    The bottom  5  of the storage box  2  has a profiling in the form of bottom projections  7  and bottom depressions  7 ′, which are arranged in an alternating manner at least in sections in the longitudinal direction of the storage box  2 . Thus, as an example, two bottom depressions  7 ′ with a bottom projection  7  arranged therebetween are provided adjacent to each through-opening for a flexible reinforcing loop element  3  in the present embodiment. However, any other number of bottom projections and depressions is also possible within the scope of the present invention, provided that these are arranged in an alternating manner. 
         [0030]    The side walls  6  similarly each have a wall profiling in the form of wall projections  8  and wall depressions  8 ′, which are arranged in an alternating manner in the longitudinal direction of the storage box  2 . Intermediate surfaces  13  that are of different sizes are respectively provided between the bottom projections and depressions and/or between the wall projections and depressions. 
         [0031]    The dimensions of the respective projections and depressions  7 ,  7 ′,  8 ,  8 ′ can be varied within a large range within the scope of the present invention. In the present embodiment, the bottom projections  7  and the bottom depressions  7 ′ each have a depth (an extension perpendicular to the bottom  5 ) of 3 mm, which results in a total depth of interlock of 6 mm. Similarly, the wall projections  8  and wall depressions  8 ′ each have a height of 2 mm, which results in a total depth of interlock of 4 mm in the region of the side walls  6 . 
         [0032]    Schematically shown in  FIG. 1   b  is a perspective view of a second embodiment of a storage box  2  in the region between reinforcing loop elements that are not shown herein. This embodiment firstly differs from the one shown in  FIG. 1   a  in that a larger number of bottom projections  7  and bottom depressions  7 ′ is arranged along the bottom  5  in a continuously alternating manner. Furthermore, the bottom projections  7  and bottom depressions  7 ′ are designed in a trapezoidal manner in the present embodiment and comprise flanks  7 ″ that are aligned substantially perpendicular to the bottom  5 . Even though in  FIG. 1   b , intermediate surfaces  13  between the bottom projections  7  and bottom depressions  7 ′, the interlocking with the surrounding concrete can be further increased by making the intermediate surfaces  13  narrower or by omitting them completely such that the bottom projections  7  and bottom depressions  7 ′ directly follow one another. 
         [0033]    The storage box  2  shown in  FIG. 1   b  furthermore differs from the embodiment shown in  FIG. 1   a  owing to the design of the wall projections and depressions. Even though only wall projections  8  are shown in  FIG. 1   b , the embodiment shown in  FIG. 1   b  can also comprise alternately arranged wall projections and depressions in accordance with the embodiment shown in  FIG. 1   a . Regardless hereof, the wall projections  8  in the embodiment shown in  FIG. 1   b  are configured such that in a direction substantially perpendicular to the bottom  5 , they have a lower anchoring resistance in concrete than in a direction differing herefrom. To be more precise, the wall projections  8  (and the wall depressions  8 ′ that are not shown here) have an elongated form that extends substantially perpendicular to the bottom and tapers in a wedge-shaped manner in the direction extending away from the bottom  5 . This results in a reduced loading of the flanks of the respective concrete part that abut the side walls  6 . 
         [0034]      FIG. 1   c  schematically shows a perspective view of further embodiments of the storage box  2 .  FIG. 1   c  thereby in particular illustrates different design possibilities for the wall depressions  8 ′, with it also being possible in  FIG. 1   c  (even though it is not shown) to provide correspondingly alternating wall projections and wall depressions. A number of designs of the wall depressions  8 ′ (and corresponding alternately arranged wall projections  8 ) that are conceivable within the scope of the present invention are schematically shown in the bottom area of  FIG. 1   c . All of these designs have an elongated shape that can also be formed, for example, by a group of several round or other shapes. It can furthermore be seen in  FIG. 1   c  that a tapering design of the shapes is preferred in order to hereby minimise the loading of the flanks of the respective concrete part that abut the side walls  6 . The wall depressions  8 ′ can thereby taper both widthwise and lengthwise. 
         [0035]    The design of the bottom projections  7  and bottom depressions  7 ′ shown in  FIG. 1   c  substantially corresponds to the design shown in  FIG. 1   d , with a round shape instead of a rectangular shape being used herein. 
         [0036]      FIG. 2   a  schematically shows a sectional view of another storage box of a connecting device according to the present invention, by means of which different embodiments will be explained as regards the design of the bottom projections and depressions.  FIG. 2   b  schematically shows, as an example, different sectional views along the line A-A in  FIG. 2   a . It must, however, be noted that the sectional views shown in  FIG. 2   d  are equally applicable for a section made in  FIG. 2   a  in the region of the wall projections  8  and wall depressions  8 ′. 
         [0037]    As is apparent from  FIG. 2   b , the bottom projections  7  and bottom depressions  7 ′ (and/or wall projections  8  and wall depressions  8 ′) can be designed in very different manners within the scope of the present invention, with it being possible on the whole to summarise the design as having an undulated or serrated form. The individual projections  7  and depressions  7 ′ can thereby be separated from one another by means of preferably narrow intermediate surfaces or can also directly follow one another. The bottom projections  7  and bottom depressions  7 ′ can also each be formed by two or more projections or depressions that are grouped together, as is shown, for example, in the third design from the bottom in  FIG. 2   b.    
         [0038]      FIG. 2   a  furthermore shows two variants for the design of the wall projections  8  and wall depressions  8 ′. Whereas the wall projections  8  and wall depressions  8 ′ shown to the right of  FIG. 2   a  have a constant height, the wall projections  8  and wall depressions  8 ′ shown to the left of  FIG. 2   a  are designed in a tapered manner (with a decreasing height), which has the advantages for the load-bearing behaviour that were discussed above. 
         [0039]    The use of the connecting device  1  according to the invention for connecting concrete parts or precast concrete parts  20  is schematically shown in  FIG. 3  in a perspective view. The connecting devices  1  are concreted into the end faces  20 ′ of the precast concrete parts  20  in such a manner that the interior defined by the side walls  6  and containing the reinforcing loop elements  3  is facing outwards. The precast concrete parts  20  are then placed together at their end faces  20 ′, thereby forming a casting joint  4  between adjacent connecting devices  1 . The reinforcing loop elements  3  are moved out of the storage boxes  2  in such a manner that they overlap with a corresponding reinforcing loop element  3  of the adjacent storage box  2 . 
         [0040]    A transverse reinforcement in the form of a reinforcing rod  16  is then introduced through the overlapping reinforcing loop elements  3 , whereupon the casting joint  4  can be filled with a suitable casting mortar. A shear-force-transmitting connection (as well as a normal force-transmitting connection) is achieved in this manner between the two precast concrete parts  20 . 
         [0041]    A top view of the part connection as shown in  FIG. 3  can be seen in a partial schematic view in  FIG. 4 . Even though the precast concrete parts  20  are not shown in  FIG. 4 , it can be seen that the respective bottom projections  7 , bottom depressions  7 ′, wall projections  8  and wall depressions  8 ′ enable an effective interlocking both between the connecting device  1  and the concrete of the precast concrete parts as well as between the connecting device  1  and the mortar to be provided in the casting joint  4 . 
         [0042]    It is furthermore apparent from  FIG. 4  that the storage box  2 , in particular the width b of the bottom  5 , the height h and the incline a of the side walls  6 , is configured such that the two opposite storage boxes  2  can be pushed closely together so as to form as small a casting joint  4  as possible, which can precisely accommodate the respective flexible reinforcing loop elements ( 3 ) in the folded-out state, including a tolerance zone. For this purpose, the width b of the bottom  5 , the height h and the incline a of the side walls  6  are advantageously adapted in the present embodiment to the progression of the respective reinforcing loop element  3 .