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FIELD OF THE INVENTION 
     The present invention refers to a device for forming joints in concrete works or in works of other materials such as cemented gravel, in which the shrinkage phenomenon occurs, and more particularly to a device allowing for the slabs or other concrete members separated by the joints to be embedded with one another, or embedded in one direction and articulated in the other. 
     The invention is applicable in linear works such as streets, roads, canals, collectors, highways, railways, docks, in surface works such as port and airport subgrades, as well as in spatial works such as walls, tanks, floor slabs, roofings, prefabricated articles and dams. 
     BACKGROUND OF THE INVENTION 
     Spanish patent application ES 2,149,103 A1 of the same applicant discloses a process of articulated interlocking between concrete slabs achieving that the edges of said slabs have recesses and projections interlocking with one another in adjacent slabs. 
     The essential element for this is the use of means placed alternately on either side of the plane of the axis of the joint perpendicular to the ground, tilted with the same angle with regard to the ground, and the tilting direction alternately varying on either side of said plane. As the concrete cracks due to shrinkage or due to the application of loads, these means allow the formation of said recesses and projections. 
     Said patent discloses several concrete means formed from metal meshes which, although they do achieve the mentioned objective, have some drawbacks which are aimed to be solved by the present invention. 
     SUMMARY OF THE INVENTION 
     In the description of the present invention, and to facilitate the understanding thereof, a regular pavement on a subgrade or ground will be used as an example of a concrete work in which the device for forming joints object of the present invention is applied. The concreting process accordingly consists of the formation of a concrete layer of uniform height on the subgrade or ground in question. For their part, the joints formed by the shrinkage of concrete imply dividing the pavement into slabs. 
     A person skilled in the art will easily understand that if the upper side of the pavement is referred to as a horizontal surface, it is because it is assumed that the surface of the ground is horizontal, this not limiting the application of the invention to horizontal pavements. A person skilled in the art will likewise easily understand that if the concrete work is not a pavement but rather a wall or a canal, the meaning of the terms such as upper side, ground or slab must be translated to the different typology of these works. 
     Therefore the object of the present invention is a device for forming contraction joints in concrete works constituted of a plurality of trays of a concrete divider material assembled on stiff linear members in an alternating manner on either side of the superficial crack line on the upper side of the concrete surface, and leaving gaps between them to allow for the cracking. 
     The device can also include supports for fixing the position of said stiff linear members and facilitating the correct positioning of the trays. 
     Said trays are preferably configured in the form of a broken surface with an upper portion and a lower portion parallel and tilted with regard to the horizontal plane, forming an acute angle therewith, and with at least one almost horizontal portion slightly tilted downwards, intended for forming notably horizontal adjacent slab support surfaces. 
     The device preferably includes a waterproofing joint arranged along the device on the upper portion of the plurality of trays and the gaps between them. 
     This waterproofing joint furthermore serves to indicate the site where the cracking of the concrete is to occur, which will be alternately “directed” on either side of said joint in different areas defined by said trays in order to leave the edges of the members resulting from the cracking alternately supported with one another. The cracking automatically occurs due to shrinkage or due to load. 
     The almost horizontal portion of the trays determines that the crack is notably horizontal in the corresponding areas of the concreting members, an efficient support between adjacent slabs is thereby obtained even though the crack width is large. The transmission of vertical loads and an embedding are achieved with such notably horizontal crack area when tensions occur on the upper side. When the load is on the joint, its behavior is that of a ball joint. 
     The purpose of this invention is similar to that of the invention disclosed in ES 2,149,103 A1: to provide a means for eliminating the problems associated to shrinkage of the concrete by achieving the embedding of the adjacent slabs formed by the contraction joint, thereby achieving a substantial improvement in the carrying capacity of concrete pavements with the same type and amount of material. However, the device object of this invention is different from those disclosed in ES 2,149,103 A1. 
     Other features and advantages of the present invention will be understood from the following detailed description of an illustrative and by no means limiting embodiment thereof in relation to the attached drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic perspective view of a device for forming contraction joints in concrete works including a plurality of trays supported at their ends on a triangular support, which are assembled on stiff linear members. 
         FIG. 2  shows a tray formed by two half-trays including an almost horizontal central portion and openings regularly distributed on its upper and lower portions. 
         FIGS. 3   a  and  3   b  show schematic elevational and plan views, respectively, of a device for forming joints using half-trays such as those shown in  FIG. 2 . 
         FIG. 4  shows an elevational view of a waterproofing joint suitable for a device for forming joints using half-trays such as those shown in  FIG. 2 . 
         FIGS. 5   a  and  5   b  show elevational views of the ends of two adjacent slabs in the joint formed using the device illustrated in  FIGS. 2 and 3  in areas occupied by trays arranged on different sides of the superficial crack line. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In reference to  FIG. 1 , it can be seen that the device  1  for forming contraction joints in concrete works according to the invention includes three basic components: members formed by equal trays  3 ,  3 ′, supports  5 ,  5 ′ and stiff linear members  7 ,  9 ,  11 . 
     The device  1  is assembled in situ at the work site in question, in a warehouse or in any suitable site, in the position and with the length provided for forming the contraction joints. 
     Said trays  3 ,  3 ′, which will usually be prefabricated, are alternately arranged on either side of the superficial line provided for the crack of the concrete, situated on the same vertical plane as the stiff linear member  11 , usually leaving gaps  16  between them, although it may be useful to position the trays  3 ,  3 ′ one against the other for certain applications. 
     A fourth component of the device  1  (not shown in  FIG. 1 ) is a waterproofing joint  40  ( FIG. 4 ) situated on the upper portion thereof. 
     Although the supports  5 ,  5 ′ are not indispensable, it is convenient to use them as correct positioning means of the stiff members  7 ,  9 ,  11 . They additionally facilitate positioning of the trays  3 ,  3 ′ with the suitable inclination. 
     The alternating arrangement of trays  3 ,  3 ′ defines a triangular prismatic shape of the device  1 . 
     In the preferred embodiment shown in  FIG. 2 , a tray  12  formed by two half-trays  14 ,  15 , equal with the exception of the position of the supports  30 ,  31 , can be seen. Half-tray  15  has a broken surface form with an upper portion  17  and a lower portion  19  that are parallel and tilted at an acute angle I with regard to the horizontal plane, and a central, almost horizontal portion  21 . The upper portion  17  and lower portion  19  include regularly arranged open areas  22 . 
     It is calculated that the suitable inclination of portions  17  and  19  with regard to the horizontal (angle I in  FIG. 2 ) must be comprised between 40° and 80°, and that of the central portion  21  (angle C in  FIG. 2 ) must be comprised between 0° and 15°. The inclination of portions  17  and  19  can be different. 
     The half-tray  15  is supported at one of its ends on the triangular type support  31 , with a broken side such as the surface of the tray  15 , with an inner reinforcement  33 . The support  31  has orifices  35 ,  37  at its lower base through which the stiff linear members allowing the assembly of the device are passed. The half-tray  15  in turn has a conduit  25  at its lower portion for the same purpose, and therefore with the same section, although it does not necessarily have to be completely closed as is shown in  FIG. 2 . 
     On the other hand, the upper edge  27  of the half-tray  15  is configured in a U shape to facilitate the assembly of a waterproofing joint  40  such as the one shown in  FIG. 4 , wherein two hooks  41 ,  43  are seen, one on either side, for gripping the cracked concrete slabs, lips  45 ,  47  allowing for the horizontal separation thereof. 
     The head or upper edge  27  of the half-tray  15  includes small projections assuring the fixing of the joint  40  by means of a clipping mechanism. 
     The half-tray  15  and the support  31  in this embodiment are solidly joined together at one end. In alternative embodiments, it is possible for the supports to not be solidly joined to the half-tray and to be situated at the center thereof rather than at one of its ends. A determining factor in the choice of either alternative is the height which the device must have. In this sense, it can be observed that the configuration shown in  FIG. 2  allows for the assembly of a double-height device by fitting the conduits  25  of one row of semi-trays in the heads  27  of another row of semi-trays. 
     In reference to  FIGS. 3   a  and  3   b , a device  1  for forming joints with trays  12 ,  12 ′ alternately arranged on either side of the superficial crack line  24  (coinciding with the stiff linear member  11 ) with gaps  16  between them can be seen. The trays  12  and  12 ′ are formed by pairs of half-trays  14 ,  15 , which are equal with the exception that each of them is solidly joined to the triangular support  31  at a different end, and they are assembled on stiff linear members  7  and  9  which are made to pass through the orifices  35  and  37  of the supports  30 ,  31  and through the conduit  25  of the trays  15 . 
     On the end far from the supports  30 ,  31 , the half-trays  14  and  15  can be configured such that they can be fitted together. 
     A third linear member  11  has been added in  FIGS. 3   a  and  3   b  which, in this case, serves to stiffen the waterproofing joint  40 , and which is situated in the cavity  49  of its lower portion, which is assembled on the upper edge  27  of the half-trays  14 ,  15 . 
     The material constituting the trays  3 , the semi-trays  14 ,  15  and the supports  5 ,  31  can be polypropylene, PVC, polyamide, steel sheet or a sheet of another material suitable for serving as a concrete divider member. 
     The material constituting the waterproofing joint  40  can be gum, PVC, rubber or another waterproof material. 
     Highly stiff plastic bars or steel bars can be used as stiff linear members  7 ,  9 ,  11 . 
     All the components of the device are susceptible to prefabrication. Their reduced weight and their shape allow for transporting them in stacks to the work site where they are assembled in the manner indicated and positioned on the ground in the sites provided for the joint. 
     Once assembled, the device for forming contraction joints according to the present invention has a certain bending capacity allowing it to adapt itself to the surface on which the concrete will be poured even if it is not perfectly level. Its configuration and particularly the presence of openings in the trays and supports facilitates the positioning of the concrete without moving the device. As a complement, nails for fixing it to the terrain immobilizing the members  7  and  9 , and therefore the device  1 , are needed. 
     The fixing of the waterproofing joint  40  in the head  27  of the semi-trays  14 ,  15  in turn assures the correct positioning thereof. The waterproofing joint  40  can open its lips  45 ,  47  and be anchored to the concrete slabs on either side of the crack, allowing the expansion and shrinkage of the concrete, being closed on the underside in order to be waterproof both in its upward and downward movement. As previously indicated, a stiff linear member  11  can be found inside this waterproofing joint  40  if greater stiffness of the assembly were required. 
     In this sense, the joint  40  could be carried out such that the lips  45  and  47  were joined at their lower portion, i.e. at the upper portion of the cavity  49 . 
     The device for forming contraction joints according to the present invention includes gaps  16  between alternating trays  3 ,  3 ′;  12 ,  12 ′ so that the crack of the concrete resulting from shrinkage or from the action of a load can easily vary its orientation to either side of the superficial crack line by following the surfaces of said trays  3 ,  3 ′;  12 ,  12 ′. 
     The optimum size of the gaps  16  between alternating trays  3 ,  3 ′;  12 ,  12 ′ is comprised between one and two times the length of the base of the support of said trays. 
     The device  1  for forming contraction joints according to the invention can also be used as a formwork, which is useful for demarcating the conclusion of a work at the end of a working day or for carrying out a linear work in two semi-roadways at different moments in time in which a longitudinal joint is to be formed according to the present invention. For these special cases, the trays and triangles cannot incorporate openings and they must be positioned with no gaps between two alternating trays in order to achieve an effective closing preventing the concrete from coming out. 
     In reference to  FIGS. 5   a  and  5   b , the embedding occurring between the slabs  50  and  52  formed in a pavement (in concrete works other than pavements, the members separated by the joints would have another shape), which is facilitated in the event of very wide cracks due to the existence of flat surfaces  53 ,  54 ;  53 ′,  54 ′ corresponding to the areas  21  of the trays  12 ,  12 ′, is observed. 
     As concrete cracks, the two slabs  50 ,  52  are formed with a different configuration in the areas corresponding to the alternating trays  12 ,  12 ′, respectively. 
     In the area corresponding to one tray  12  ( FIG. 5   a ), the horizontal span  54  of slab  52  is situated above the horizontal span  53  of slab  50 , and slab  52  is prevented by slab  50  from moving downwards. 
     However, in the area corresponding to tray  12 ′ ( FIG. 5   b ), span  54 ′ of slab  52  is situated under the horizontal span  53 ′ of slab  50 . Therefore, in this area slab  52  is prevented from moving upwards since the horizontal span of slab  50  is above it. Therefore the shear stresses are transmitted among the slabs and, generally, among the cracked members when the concrete works are other than pavements. 
     On the other hand, the bending moments are also transmitted. If the area of the joint were to be raised up due to the effect of an internal load of the slab  50 , span  53  will be higher than span  53 ′ as it is farther from the load tending to sink the slab in the center and raising it up on the edge. According to  FIG. 5   b , span  53 ′ is higher than span  54 ′ of slab  52 . In turn, span  54 ′ raising up in slab  52  is higher than span  54  as it is farther from the center of the slab  52 . Therefore the order of the height or height level reached would be  53 ,  53 ′,  54 ′,  54 . This is not possible since, by looking at  FIG. 5   a , portion  54  is above portion  53 . For it to be above and below at the same time, they must be at the same height level. In other words, the line joining one support  53 - 54  with the other one  53 ′- 54 ′ is a line parallel to the horizontal (parallel to the surface). Therefore there is no turning between slabs  50  and  52 , and the bending moments are transmitted. 
     The horizontal portion  21  of the trays  12 ,  12 ′ always works under compression, therefore its durability is assured. It is recommended that it be thin and/or that its elastic limit be high so that deformation thereof by compression is small and the transmission of loads is efficient. Any downward movement of a slab must be transmitted to the other one in the same magnitude; if the downward movement is identical, the transmission of loads efficacy is 100%. In tests carried out with the falling weight deflectometer, an almost perfect behavior is reflected in a total of 60 tested cracks (mean greater than 99%, and no measurement below 93%). 
     The following advantages concerning the device for forming contraction joints according to the invention with regard to the prior art can be mentioned:
         Adaptability to the terrain.   Industrial manufacturing of the components.   Inexpensive and easy light weight transporting by pieces.   Transmission of the shear stresses even though the width of the crack is large (more than 1 cm), suitably sizing the horizontal portion of the trays.   Transmission of the bending moments if the central surface is completely horizontal (parallel to the grade line).   Good integration of the waterproofing joint.   The waterproofing joint does not drag the device for forming joints if it slightly projects from the grade line, given that it is a member that can give. For this purpose it is of interest, as shown in  FIG. 2 , that the axis of the head  27  is moved with regard to the axis of portion  17  of the tray.   The philosophy is not to reinforce a concrete area and prevent a crack from advancing in one direction, but rather to weaken an area in order to guide the crack, which is easier and less expensive.   It is possible to combine the trays so that an embedding occurs in the two directions of the bending moment.       

     An especially interesting advantage of the present invention concerns railways, given that it allows for the construction thereof on the basis of concrete, the respective slabs being duly embedded with one another. This feature would allow for considering the elimination of the current rails as the concrete railway is able to carry out their function. 
     The present invention is not limited to the described embodiments, but rather to any other embodiment comprised within the scope defined by the following claims.

Summary:
The invention relates to a device for forming contraction joints in concrete works. The invention comprises a plurality of assemblies which are made from a concrete-separating material and which are mounted to rigid linear elements in an alternate manner on one side and then the other of the surface crack line on the upper face of the concrete work surface, leaving spaces therebetween for cracking. The inventive device enables the adjacent slabs formed by the contraction joint to be fixed, thereby improving the resistance performance thereof. The invention is suitable for in situ concrete works, such as roads, channels, esplanades, sewers, tunnels, railways, dykes, etc.