Abstract:
An expansion or crack joint assembly ( 32 ) utilizes a coupler ( 20 ) with or without a bottom sheet ( 34 ) to join adjacent roadway concrete slabs ( 86, 90 ) formed separately initially or continuously cast and later separated by a saw cut, which induces cracking to form a crack joint. The coupler ( 20 ) includes a casing ( 22 ), an internal component ( 24,25,62,65 ), and outer sleeve ( 26 ), and end caps ( 28,30 ). The casing ( 22 ) defines an internal chamber ( 40 ) which receives the internal component ( 24,25,62,65 ) therein. The sleeve ( 26 ) and end caps ( 28,30 ) fit over the casing ( 22 ). The casing ( 22 ) and sleeve ( 26 ) transmit loads between the concrete slabs ( 86,90 ) while the sleeve ( 26 ) and end caps ( 86,90 ) operate to reduce stress concentrations. The bottom sheet ( 34 ) inhibits water from entering the expansion or crack joint assembly ( 32 ) from below, if used, and prevents pumping. In various embodiments, the internal component is a spring disk ( 24,25 ), a flat, circular disk ( 62 ), and a structural material ( 65 ), such as concrete, which substantially fills the internal chamber ( 40 ).

Description:
RELATED APPLICATION 
     This is a continuation application of application Ser. No. 09/158,397 filed Sep. 22, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with improved, preferably prefabricated expansion or crack joint couplers particularly designed for use in joining concrete roadway slabs in order to properly transfer vertical forces between concrete slabs while minimizing stress concentrations experienced using conventional dowels at expansion or crack joints. More particularly, the invention pertains to an expansion or crack joint coupler including a steel which bridges joints between concrete slabs with the ends of the coupler embedded in the slabs. In preferred forms, substantially circular disks are inserted in the coupler and its ends are closed with end caps with a multifunction reinforcing sleeve centrally positioned around the outside of the coupler. Alternatively or additionally, the coupler is filled with a structural material such as concrete. 
     Our invention keeps the strength and stiffness of the pavement at a joint equal to that in the middle of a pavement slab to the extent possible, while keeping the tensile stress low in the slab at a joint so that in the normal shrinkage and expansion of pavements, adjacent slabs will separate at the joints instead of by developing cracks in the middle of the slabs. In doing this, the new coupler transfers bending moments as well as shearing forces. 
     One of the main purposes of this invention is to transfer shear forces and bending moments from the loaded slab to unloaded slab as heavily loaded wheels cross the joints or cracks while keeping the differential deflection between the slabs a minimum, and decreasing the vertical deflection of the slabs at the joints. 
     2. Description of Prior Art 
     In the construction of concrete roadways, it is common practice to install expansion or crack joint assemblies at spaced locations, so that the completed roadway can properly expand and contract under varying temperature and environmental conditions. Typical expansion or crack joint assemblies make use of a plurality of laterally spaced apart shear transfer devices having elongated force transmission members. 
     With the presently used expansion or crack joints the PCC (Portland Cement Concrete) slabs usually deteriorate near the crack joints. This deterioration is caused by excessive compressive or bearing stresses between the concrete and the dowels. These cause powdering of the concrete at the surface of the dowels near the joints between the slabs, which in turn creates voids around the dowels into which moisture and de-icing salt water flow causing serious corrosion of exposed steel. The powdered concrete abrades anti-corrosion coatings, which causes even previously coated dowels to corrode. Compressive stresses caused by heavy wheel loads also cause lateral splitting forces along the dowels, another compressive failure problem. 
     The bending stiffness of currently used steel dowels and other dowels in experimental stages are not great enough to transfer the moments required by current traffic, or to reduce warping at the corners of the slabs. 
     At extreme temperatures, the steel dowels can be compressed between the concrete slabs, again causing excessive stress in the concrete, and even deforming the dowel and crushing the concrete at the ends of the dowels. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above and provides an improved expansion or crack joint coupler. By virtue of a unique outer casing defining an internal chamber and having a structural component inserted in the internal chamber, the improved expansion or crack joint coupler provides increased stiffness, strength, and load transferring ability while reducing weight and stress concentrations. 
     Broadly speaking, the expansion or crack joint coupler of the present invention has a casing with two ends and a central region therebetween. The casing defines an internal chamber and is designed to be embedded in adjacent concrete slabs and to extend across an expansion or crack joint between the slabs. An internal structural component is inserted into the internal chamber to enhance the properties of the casing. 
     In a preferred embodiment, two tapered spring disks are inserted into the internal chamber of the casing, which is preferably structural steel pipe. The spring disks are positioned approximately equal distances on opposite sides of the casing center, and each spring disk includes a rigid smaller diameter portion and a compressible larger diameter portion which is ring-shaped. The compressible portion of the disk defines a plurality of slits equal spaced around the circumference of the disk, and the compressible portion preferably face outward toward the end of the casing. 
     In another preferred embodiment, a single solid disk is centrally positioned in the internal chamber. The disk is rigid and preferably fits tightly in the casing chamber. 
     In still another preferred embodiment, the casing is filled with a structural material. The structural material is preferably concrete, but can be any material with appropriate stiffness. 
     There is further provided in the practice of the invention a novel outer reinforcing sleeve and a novel pair of end caps. The sleeve is preferably shorter than the casing and is centrally positioned on the casing. The ends of the sleeve are advantageously rounded to reduce stress concentrations, and if a steel sleeve is used, rubber end rings with rounded corners preferably abut the ends of the sleeve. The end caps close the ends of the casing and preferably define an opening receiving the ends of the casing therein. The end caps can also include a plurality of gripping bumps on their outer surface. Both the sleeve and the end caps are preferably formed with a material that is softer than the casing thereby reducing stress concentrations. 
     There is still further provided in the practice of the invention a novel expansion or crack joint assembly in which two adjacent concrete slabs are positioned to define a narrow gap therebetween. A sheet is positioned beneath the slabs and covers the gap to prevent pumping effects. Preferably, the coupler described above is embedded in the concrete slabs and extends across the expansion or crack joint. 
     The invention can be used to connect slabs having expansion joints provided for beforehand; or for those which are cast continuously and then caused to crack at predetermined places (where the couplers are placed before casting) by the use of saw cuts made in the pavement at the proper time after casting the continuous pavement. The invention can be used for expansion joints of concrete structures other than pavements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a transverse cross sectional view of an expansion joint assembly according to the present invention and including an expansion or crack joint coupler according to the present invention; 
     FIG. 2 is a fragmentary, enlarged, cross sectional view of an end cap of the expansion or crack joint coupler of FIG. 1; 
     FIG. 3 is a perspective view of an internal structural component of the expansion or crack joint coupler of FIG. 1; 
     FIG. 4 is a cross sectional view of the internal structural component of FIG. 3 having a tapered feature thereof exaggerated for illustrative purposes; 
     FIG. 5 is a transverse cross sectional view of an alternate expansion or crack joint coupler according to the present invention; and 
     FIG. 6 is a transverse cross sectional view of another alternate expansion or crack joint coupler according to the present invention and having an adhesive coating thereof enlarged for illustrative purposes. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings, FIG. 1 depicts a preferred expansion or crack joint coupler  20  having a casing  22 , internal structural components  24 ,  25 , a reinforcing sleeve  26 , and end caps  28 ,  30 . The coupler  20  is part of an expansion or crack joint assembly  32 . In a crack joint, there is no initial separation between slabs  86 ,  90 , but saw cuts are made in the top of a continuous concrete slab to induce cracks where the couplers  20  are located. A bottom sheet  34  is used where local conditions make its use advisable. 
     In greater detail, the casing  22  is elongated between two ends  36 ,  38  having a center therebetween and defines an internal chamber  40  therein. The casing normally ranges in length from approximately 18 inches to approximately 20 inches, but the length is not critical. The casing is preferably a hollow tubular body and has a constant annular wall having an outer surface  42  and an inner surface  44  with a preferred inner diameter of approximately 1.5 inches. Thus, the internal chamber is essentially cylindrical. The preferred casing material is structural steel. Therefore, the casing is preferably a standard size of extra strong steel pipe. 
     Referring additionally to FIGS. 3 and 4, the internal structural components  24 ,  25  are preferably identical and comprise tapered spring disks. Each tapered spring disk  24  includes a substantially rigid portion  46  and an integral, compressible portion  48 . The disk  24  is substantially circular but its outer annular surface  52  tapers slightly inward from the rigid portion  46  to the compressible portion  48 . 
     The rigid portion  46  is solid and has a smallest outer diameter approximately equal to the inner diameter of the casing. The rigid portion has an inner side  54 , and an outer side  56 . The rigid portion forms a base for the compressible portion. 
     The compressible portion  48  is an annular ring, and the outer diameter of the compressible portion is slightly larger than the inner diameter of the casing  22 . Thus, the compressible portion outer diameter is generally larger than the smaller rigid portion outer diameter. The compressible portion defines a plurality of slits  58  substantially evenly spaced around the circumference of the compressible portion. The slits  58  form spring tabs  60  extending from the outer side  56  of the rigid portion  46  to form a cup shape. 
     The spring disks  24 ,  25  are positioned inside the internal chamber  40  on opposite sides of the casing center with the outer sides  56  facing the ends  36 ,  38  of the casing and with the inner sides  54  facing each other. The spring disks are preferably positioned equal distances of approximately 1.5 inches from the casing center. 
     Referring to FIG. 5, in an alternate embodiment, a coupler  61  has an internal structural component which comprises a single circular disk  62  positioned substantially centrally in the casing  22 . The circular disk  62  is preferably flat and sized to fit tightly in the casing. 
     Referring to FIG. 6, in another alternate embodiment, a coupler  63  has an internal structural component which comprises a structural material  65  filling the internal chamber. The preferred structural material is concrete. The concrete can fill substantially the entire internal chamber  40  or it can fill in around the circular disk  62 . 
     Referring to FIG. 1, the reinforcing sleeve  26  is preferably cylindrical and is sized to slide over the outer surface of the casing  22 . Thus, the sleeve inner and outer diameters are larger than the casing outer diameter. The sleeve  26  has a sleeve length of approximately 5 inches and is thus shorter than the casing length. The sleeve is substantially centrally positioned around the casing, and the annular wall of the sleeve is preferably of constant diameter. The butt ends  64  of the sleeve are preferably rounded, and the sleeve material is preferably softer than the casing material. The preferred sleeve material is PVC. Referring additionally to FIG. 6, the sleeve is preferably fixed in a central position by an anti-corrosion adhesive coating  66  on the outer surface  42  of the casing. 
     FIG. 6 also shows an alternate reinforcing sleeve  68  which is preferably made from structural steel. Because of its strength, the steel sleeve thickness is less than the PVC sleeve thickness. When the steel sleeve is used, rounded end rings  70  are positioned around the casing  22  and abut the opposite ends of the steel sleeve  68 . The upper, outer corners  72  of the end rings  70  are rounded, and the rings  70  are made with a ring material preferably softer than the steel sleeve and casing materials. The ring material is preferably rubber or PVC. The adhesive coating  66  also fixes the end rings  70  in position next to the opposite ends of the steel sleeve  68 . 
     Referring to FIGS. 1 and 2, the end caps  28 ,  30 , which are arcuate in cross-section, each define an end cap opening  74  and are formed with or without concrete gripping bumps  76  on an outer surface  78  thereof. The end cap material is a synthetic resin material, preferably PVC which is softer than the casing material, and the end caps substantially close and seal the ends  36 ,  38  of the casing  22  to keep moisture out of the casing. 
     The end cap openings  74  are sized to frictionally couple to and cover the ends of the casing  36 ,  38 . To that end, the openings  74  are slightly smaller than the casing outer diameter. However, the openings have a widening mouth  80  (FIG.  2 ), which is defined by an arcuately tapered circumferential edge and has a diameter slightly greater than the casing outer diameter to aide in assembly. The openings  74  have arcuate sections  82 , which are, for example, parabolic or hemispherical in shape. The openings also have substantially straight walled sections  84  which extend approximately 1 inch over the ends of the casing. 
     The end cap has an integrally formed closed end body with an open mouth section and a closed endmost section which is arcuate in cross-section. The mouth section and endmost section are defined by an inner surface presenting an inner mouth segment and a closed, concave segment, and an outer surface presenting an outer mouth segment and a convex segment. The inner mouth segment is an elongated, substantially circular in cross-section surface, and the mouth is adapted to receive the end of an expansion joint force transmission member therein. The convex segment surface presents a series of outwardly extending, arcuate in cross-section projections whic comprise the bumps  76 . The outer mouth segment preferably tapers from the convex segment to the outer edge of the inner mouth segment. The concave segment extends from the inner mouth segment and defines a hollow region within the end cap. 
     If used, the gripping bumps  76  are evenly spaced over the outer surface  78 , which preferably is generally frustospherical, of the caps and are preferably arranged in a symmetrical pattern. The bumps are preferably integrally formed with the caps. Alternatively, the outer surfaces  78  of the caps are smooth. 
     Referring to FIG. 6, the end cap material can also be steel. The steel end caps  77 ,  79  are configured similarly to the PVC end caps  28 ,  30 , but because of their higher strength, the steel end caps  77 ,  79  are thinner. The outer surface  81  of the steel end caps  77 ,  79  can have gripping bumps  83  or be smooth. 
     Referring again to FIG. 1, the expansion or crack joint assembly  32  connects a first concrete slab  86  having a first end  88  and a second concrete slab  90  having a second end  92 . The first concrete slab is adjacent the second concrete slab, so that the first end  88  and the second end  92  are positioned to face each other with a narrow expansion gap  94  therebetween. The gap  94 , which has been enlarged for illustration, can be filled with an expandable material or component (not shown) if desired. 
     In a crack joint, the gap  94  does not exist, but a saw cut is made in the top of the slab. The couplers for crack joints are put in place before continuous casting of PCC pavement in which cracks are induced by saw cuts in the previously continuous concrete slabs at locations of previously placed rows of couplers. The cuts induce cracks which propagate from the bottom of the cut to the bottom of the slab. 
     The bottom sheet  34 , when used, is positioned beneath the concrete slabs  86 ,  90  and has a width sufficient to cover the gap  94  between the slabs. The sheet is placed on the subgrade before the concrete is cast. The purpose of the sheet  34  is to reduce pumping. The sheet is preferably 18 inches wide, and is substantially impenetrable to water. The coupler  20  is configured for embedment in the concrete slabs  86 ,  90  and extends across the expansion gap  94  or the cracked joint which will develop under the saw cut. 
     The expansion or crack joint coupler  20  is preferably assembled and then transported to construction sites. To assemble the coupler shown in FIG. 1, the casing is cut to length, and the adhesive coating  66  (FIG. 6) is applied. Before the adhesive coating cures the sleeve  26  is positioned over the central region of the casing. Once the adhesive is cured, the sleeve  26  is fixed in place. Before or after the sleeve is positioned, the spring disks  24 ,  25  are pressed into the internal chamber. The rigid portions  46  are sized to slide through the internal chamber, preferably with some friction, and the compressible portions  48  are sized to compress the spring tabs inwardly when forced into the internal chamber. Thus, the compressible portions  48  hold the spring disks in place. The mouths  80  of the end caps  28 ,  30  are aligned with the ends  36 ,  38  of the casing  22  and press fit over the casing and adhesive coating. 
     The assembly of the alternate coupler  61  shown in FIG. 5 is similar to that of the coupler  20  shown in FIG. 1 with the exception that only the single circular disk  62  is pressed into the casing. The assembly of the coupler  63  shown in FIG. 6 is also similar except that the end rings  70  are also positioned before the adhesive cures, and the concrete is poured into the internal chamber  40  and cured before the end caps  77 ,  79  are put in place. 
     In the completed expansion or crack joint assembly  32 , the casing and sleeve transmit forces between the concrete slabs. Thus, the casing and sleeve act as elongated force transmission members bridging the expansion or crack joint and having two opposed ends. The spring disks  24 ,  25  maintain the casing&#39;s cylindrical shape under bending loads, so that the coupler is stiffer allowing the casing to transmit such loads with increased efficiency. Thus, there is less relative bending between adjacent concrete slabs. Because the spring disks are spaced apart, the positioning of the casing center relative to the gap  94  is not critical. The stress concentrations that normally occur in the center of the coupler are minimized by the increased diameter of the casing  22  and the PVC sleeve  26 . That is, the coupler has a larger bearing area, and thus, the bearing stress is less. The softer sleeve material also minimizes stress by compressing slightly and dampening vibrations thereby avoiding stress fractures in the concrete. 
     The rounded ends  64  of the sleeve  26  prevent a stress concentration at the ends as would occur at a sharp edge. The sleeve  26  also protects the adhesive coating  66  (FIG.  6 ), which preferably inhibits corrosion. 
     The end caps  28 ,  30  protect the adhesive coating  66  on the ends of the casing  22 . The end caps also minimize stress concentrations at the ends  36 ,  38  of the casing because they are arcuate and are made from a relatively soft end cap material. The flexibility of the PVC end caps also reduces compressive thermal stress. The PVC sleeve and end caps also allow small angular deformation of the concrete to further alleviating thermal stress, and both the sleeve and end caps operate to reinforce the respective portions of the casing. The concrete gripping bumps  76  operate to fix the end caps in the concrete slabs. 
     The bottom sheet  34  seals against the bottoms of the slabs to inhibit water from entering the expansion or crack joint through the expansion joint gap  94 , or the cracks formed under saw cuts. Specifically, the sheet  34  keeps the gap from acting as a pump as the gap repeatedly narrows and widens due to the expansion and contraction of the concrete slabs and as differential motion and deflation of adjacent slabs occurs under loading. 
     The coupler  61  of FIG. 5 operates similarly. However, the coupler  61  is less expensive because only the simpler to manufacture, single circular disk  62  is used. Both the couplers  20 ,  61  of FIGS. 1 and 5 respectively provide approximately 150% of the strength of standard size, solid steel dowels, and because the couplers  20 ,  61  of FIGS. 1 and 5 are substantially hollow, they weigh approximately 75% less than standard size, solid steel dowels. Thus, they are much less expensive to ship to construction sites. Further, these couplers are significantly stiffer than standard solid dowels. 
     The coupler  63  of FIG. 6 also operates similarly, but provides further increased strength and stiffness. The concrete filled coupler  63  with the increased reinforcement from the steel end caps  77 ,  79  and the steel sleeve  68  provides approximately 200% greater strength than the standard size, solid steel dowel and is approximately 300% stiffer. The end rings  70  operate to alleviate stress concentrations at the ends of the sleeve  68 . 
     The coupler  20  having the spring disks and a coupler filled with concrete according to the present invention were subjected to bending and shearing tests. The same tests were performed on a solid steel dowel, a solid glass fiber epoxy dowel, and a glass fiber tube filled with concrete. The results of the tests are set forth below in table format for comparison. Table 1 shows the average results of the bending test, and Table 2 shows the average results of the shearing test. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Deflection in 0.001 inch 
               
             
          
           
               
                   
                 Steel Pipe 
                 Steel Pipe 
                 Solid 
                 Solid 
                 Glass 
               
               
                 Load 
                 Coupler with 
                 Coupler with 
                 Steel 
                 Glass 
                 Fiber with 
               
               
                 (Kips) 
                 Two Disks 
                 Concrete 
                 Dowel 
                 Fiber 
                 Concrete 
               
               
                   
               
             
          
           
               
                 1 
                 10.75 
                 13.75 
                 266.5 
                 53 
                 104.5 
               
               
                 2 
                 21.25 
                 26 
                 50.75 
                 104.67 
                 194.5 
               
               
                 3 
                 31.5 
                 36 
                 72.5 
                 147.33 
                 276 
               
               
                 4 
                 39.5 
                 47 
                 95.5 
                 186 
                 367.5 
               
               
                 5 
                 46.5 
                 55.75 
                 119.5 
                 219 
                 424.5 
               
               
                 6 
                 54.25 
                 64.75 
                 159.25 
                 249.67 
                 484 
               
               
                 7 
                 65.75 
                 73.5 
                 213.75 
                 276.67 
                 541 
               
               
                 8 
                 88.75 
                 82.5 
                 273.5 
                 300.67 
                 596 
               
               
                 9 
                 129.25 
                 94.75 
                 338.75 
                 325.67 
                 667 
               
               
                 10 
                 170.5 
                 111 
                 399.25 
                 347.67 
                 723 
               
               
                 11 
                 208 
                 132 
                 467.75 
                 371 
                 810 
               
               
                 12 
                 248.75 
                 154.25 
                   
                   
                 907.5 
               
               
                 13 
                 283.75 
                 174.75 
               
               
                 14 
                 320.75 
                 195.75 
               
               
                 15 
                 363.75 
                 217.25 
               
               
                 16 
                   
                 240.25 
               
               
                 17 
                   
                 265.5 
               
               
                 18 
                   
                 300.75 
               
               
                 19 
                   
                 330.25 
               
               
                 20 
                   
                 366 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Deflection in 0.001 inch 
               
             
          
           
               
                   
                 Steel 
                   
                   
                   
               
               
                 Load 
                 Pipe Coupler 
                 Solid 
                 Solid 
                 Glass Fiber 
               
               
                 (Kips) 
                 with Disks 
                 Steel Dowel 
                 Glass Fiber 
                 with Concrete 
               
               
                   
               
             
          
           
               
                 5 
                 31.25 
                 43 
                 47 
                 53.5 
               
               
                 10 
                 53.5 
                 71.5 
                 76.5 
                 88 
               
               
                 15 
                 85.25 
                 92 
                 94 
                 111.5 
               
               
                 20 
                 119 
                 113.5 
                 127 
                 129 
               
               
                 25 
                 146.5 
                 132.5 
                 159 
                 145.5 
               
               
                 30 
                 174.5 
                 149.5 
                   
                 166 
               
               
                   
               
             
          
         
       
     
     Thus the couplers of the present invention provide increased strength and stiffness while minimizing stress concentrations. Thus, the deterioration of expansion or crack joint assemblies is substantially decreased.