Patent Publication Number: US-6210070-B1

Title: Concrete dowel slip tube with clip

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to the art of concrete construction, and more particularly to a device for facilitating the placement of slip dowel rods within a concrete slab. 
     In the art of concrete construction, it is commonplace to form “cold joints” between two or more poured concrete slabs. Such cold joints frequently become uneven or buckled due to normal thermal expansion and contraction of the concrete and/or compaction of the underlying soil caused by inadequate substrate preparation prior to pouring of the concrete. As a means of preventing buckling or angular displacement of such cold joints, it is common practice to insert smooth steel dowel rods generally known as “slip dowels” within the edge portions of adjoining concrete slabs in such a manner that the concrete slabs may slide freely along one or more of the slip dowels, thereby permitting linear expansion and contraction of the slabs while at the same time maintaining the slabs in a common plane and thus preventing undesirable buckling or unevenness of the cold joint and in adjacent slabs. 
     In order to function effectively, slip dowels must be accurately positioned parallel within the adjoining concrete slabs. The non-parallel positioning of the dowels will prevent the desired slippage of the dowels and will defeat the purpose of the “slip dowel” application. Additionally, the individual dowels must be placed within one or both of the slabs in such a manner as to permit continual slippage or movement of the dowels within the cured concrete slab(s). 
     It is commonplace to form large concrete slabs using monolithic or continuous concrete pour methods. Such slabs are formed by continuously pouring large quantities of concrete without the use of forms or cold joints in order to reduce costs. Therefore, fracturing of the slab is prevented by including tooled joints or sawcuts in the slab where cold joints would otherwise be needed. Additionally, concrete reinforcement material such as wire mesh or segments of rebar are initially placed into the area in which the continuous pour is to be made, and in particular those areas where it is contemplated that sawcuts will be included in the resultant slab for purposes of preventing fracturing thereof. The wire mesh or other reinforcement material is preferably elevated above ground level by the placement thereof upon support blocks or “chairs”. 
     In addition to having concrete reinforcement material disposed within those portions of the slab in which a sawcut is to be made, it is also desirable to incorporate slip dowels into such portions to allow the separate sections of the slab which are defined by the sawcuts to move relative to each other while preventing any buckling or angular displacement thereof. One prior art method of incorporating slip dowels into those areas of a continuous pour where sawcuts are contemplated involves manually “stabbing” the slip dowels into predetermined locations of the uncured concrete pour. This method, however, is deficient in that there is no way to insure that the slip dowels will be manually positioned within the uncured concrete in parallel relation to each other, or will be maintained in parallel alignment to the top surface of the concrete pour during curing. As previously explained, if the dowel rods are not in parallel alignment, the separate sections of slab as defined by the sawcuts will be prevented from moving relative to each other. 
     Another prior art method of incorporating slip dowels into a monolithic pour involves manually tieing the slip dowels to the reinforcement material in parallel relation to each other prior to the concrete pour being made. Manual tieing, however, is extremely time consuming and presents significant difficulties in securing the slip dowels to the reinforcement material in true parallel relation to each other. Additionally, the tied slip dowels are susceptible to displacement or shifting when impacted by the concrete during the pour thus moving the same out of parallel alignment with each other. 
     The present invention addresses and overcomes the above-described deficiencies of prior art slip dowel placement in continuous concrete pours by providing a device that places slip dowels accurately during the pouring of such concrete slabs. In this respect, the present invention places slip dowels into a concrete slab through the use of slip tubes that are easily attached to a prefabricated support structure. Therefore, the present invention provides an accurate and easy system for slip dowel placement in a monolithic pour. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a concrete dowel slip tube for attachment to a wire mesh support structure. The slip tube comprises an elongate, tubular dowel receiving sheath having a proximal end, a distal end, an exterior surface and a hollow interior compartment extending longitudinally therein. The hollow interior compartment that is sized and configured to receive a concrete support dowel. The interior compartment has a generally circular cross-sectional configuration with a diameter between about 0.5 inches and about 1.0 inches. The longitudinal length of the sheath is between about 6.0 inches and about 30.0 inches. 
     Attached longitudinally to the exterior surface of the sheath is a clip sized and configured to frictionally retain the wire mesh support structure. The clip has a first prong portion and a second prong portion that define an arcuately contoured recess that is engagable to the support structure. The clip extends longitudinally along at least one-half the length of the sheath or from about the distal end to about the proximal end. 
     There is additionally provided a concrete dowel placement apparatus comprising a wire mesh support structure placeable upon a support surface and the concrete dowel slip tube previously described. The support structure comprises a base portion and an elevated portion having a plurality of top segments which extend in spaced, generally parallel relation to each other for attachment of the clip of a respective slip tube. Each of the top segments is configured to be in generally co-planar relationship to each other. Typically each top segment is elevated to a height of between about 2.5 inches and about 24 inches and spaced between about 6.0 inches and 30.0 inches between one another. 
     In a first embodiment of the support structure the elevated portion comprises a plurality of side segments which extend generally perpendicularly relative to respective ones of the top segments. Additionally, the base portion includes a plurality of base segments which extend generally perpendicularly to respective ones of the side segments. In a second embodiment of the placement apparatus the elevated portion of the support structure comprises a plurality of V-shaped members attached to the base portion and arranged to define multiple opposed pairs. Each of the V-shaped members define an apex such that each of the top segments are attached to and extend between the apices of a respective pair of V-shaped members. 
     The placement apparatus may be in further combination with an elongate concrete support dowel. The concrete support dowel is slidably insertable into the concrete dowel slip tube such that an end of the support dowel extends therefrom. A support foot may be further included in the placement apparatus of the present invention. The support foot is sized and configured to receive and support the end of the dowel extending from the slip tube and coaxially maintain the dowel in such position. As such, the interior compartment of the sheath defines a first axis and the dowel defines a second axis that is coaxially alignable with the first axis when the dowel is inserted into the interior compartment. The support foot is formed to be of a height which maintains the coaxial alignment of the first and second axes when the dowel support foot is placed upon the support surface and interfaced to the end of the dowel protruding from the sheath. 
     The present invention further comprises a method of supporting a monolithic concrete pour through the use of a placement apparatus having a support structure, multiple slip tubes having open ends and multiple support dowels. The method comprises attaching the slip tubes to the support structure such that the slip tubes extend in generally parallel alignment with each other. Next, the support structure is placed at a prescribed location on a support surface and the support dowels are inserted into open ends of respective ones of the slip tubes such that at least a portion of each of the support dowels protrudes from a respective one of the slip tubes. The concrete is then poured around the slip tubes and the exposed portions of the support dowels to encapsulate the same and form a monolithic concrete slab. Finally, a sawcut is made in the concrete slab along an axis perpendicular to the axes of the slip tubes. The sawcut may be formed such that the axis of the cut is extended along and in spaced relation to the open ends of the slip tubes. The slip tubes may be attached subsequent to the placing of the support structure and a support foot may be attached to each support dowel after sliding the dowel within the slip tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
     FIG. 1 is a perspective view of a concrete dowel slip tube of the present invention as used in conjunction with a wire mesh support structure constructed in accordance with a first embodiment thereof; 
     FIG. 2 is a bottom perspective view of the concrete dowel slip tube shown in FIG. 1; 
     FIG. 3 is a cross-sectional view of the concrete dowel slip tube and wire mesh support structure shown in FIG. 1 in an operative position within a monolithic concrete pour; 
     FIG. 4 is a perspective view of the present concrete dowel slip tube as used in conjunction with a support foot of the present invention and a wire mesh support structure constructed in accordance with a second embodiment thereof; 
     FIG. 5 is a top perspective view of the support foot shown in FIG. 4; and 
     FIG. 6 is an exploded view illustrating the manner in which the concrete dowel slip tube is secured to the wire mesh support structure of the second embodiment as shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same, FIG. 1 perspectively illustrates a concrete dowel placement apparatus  10  for use with monolithic or continuous pour concrete construction techniques. The placement apparatus  10  comprises a wire mesh support structure  12   a  constructed in accordance with a first embodiment of the present invention and at least one concrete dowel slip tube  14  attached thereto. As seen in FIG. 3, the concrete dowel placement apparatus additionally comprises a concrete support dowel  16  and a dowel support foot  18 . 
     CONCRETE DOWEL SLIP TUBE AND SUPPORT DOWEL 
     The slip tube  14  constructed in accordance with the present invention is used for supporting the concrete support dowel  16  slidably insertable therein. As seen in FIG. 2, the slip tube  14  is constructed from an elongate, tubular sheath  20  with an open proximal end  22  and a closed distal end  24 . The sheath  20  has a generally circular cross-sectional area with an exterior surface  26 , and an inner surface  28  which defines a hollow, longitudinally extending interior compartment  30  therewithin. Typically, the longitudinal length “L 1 ” of the sheath  20  is between about 6.0 inches and about 30.0 inches. The interior compartment  30  is sized slightly larger than the outer diameter of the concrete support dowel  16 . The outer surface  26  of sheath  20  may further be provided with ribs or ridges (not shown) to facilitate frictional retention as will be further explained below. 
     Mounted on the exterior surface  26  of the sheath  20  is a clip  32  used to releasably attach the slip tube  14  to the wire mesh support structure  12   a.  The clip  32  can be integrally connected to sheath  20  (i.e., formed from the same plastic material) or attached to the exterior surface  26  thereof. The clip  32  comprises a first prong  34  and a second prong  36  that collectively define an arcuately contoured recess  38  which is sized and configured to receive a section of the wire mesh support structure  12   a.  The prongs  34  and  36  are fabricated from a flexible material such that receipt of the wire mesh support structure  12   a  into the recess  38  facilitates a slight outward flexation of prongs  34 ,  36  and frictional retention thereof to support structure  12   a.  The clip  32  preferably has a length “L 2 ” that is at least one-half the length “L 1 ” of the sheath  20  in order to provide the necessary frictional retention to support the dowel  16 . The clip  32  retains the slip tube  14  in a position whereby the concrete support dowel  16  inserted therein is supported in a prescribed position as will be further explained below. 
     Referring now to FIG. 3, the support dowel  16  is sized such that it is slidably insertable into the interior compartment  30  of the sheath  20 . The sheath  20  is typically fabricated from a plastic material such that the support dowel  16  may freely slide therewithin. The support dowel  16  extends outwardly from the open end  22  of sheath  20  such that an extended end  40  of dowel  16  is firmly adhered by a concrete slab  42  poured thereover. The dowel  16  may be fabricated from a section of rebar or other type of material with the necessary strength to prevent buckling or angular displacement of the concrete slab  42 , as will be further explained below. Additionally, the dowel  16  may be formed with ribs or ridges (not shown) on an exterior surface thereof to facilitate frictional retention within the concrete slab  42 . 
     PREFERRED EMBODIMENTS OF THE WIRE MESH SUPPORT STRUCTURE 
     As seen in FIG. 1, a first embodiment of the wire mesh support structure  12   a  comprises a plurality of elevated portions  43   a  having top segments  44   a  and side segments  46   a.  Attached in generally perpendicular relationship to the elevated portions  43   a  are a plurality of base portions  48   a.  In order to form the first embodiment of the support structure  12   a,  two side segments  46   a,    46   a  are attached perpendicularly to a respective end of the top segment  44   a  such that each side portion  46   a,    46   a  projects downwardly toward a ground surface  50  and forms a generally U-shaped elevated portion  43   a.  Furthermore, in the first embodiment, two base portions  48   a,    48   a  are attached generally perpendicularly to a respective end of each side segments  46   a,    46   a  such that each base portion  48   a,    48   a  is disposed in generally parallel relation to the ground surface  50 . Each base portion  48   a  provides a stable support foundation for each side segment  46   a  and top segment  44   a  attached thereto. 
     The first embodiment of the wire mesh support structure  12   a  additionally comprises two top stringers  52   a,    52   a,  two side stringers  54   a,    54   a  and two base stringers  56   a,    56   a  as seen in FIG.  1 . Each top stringer  52   a  is attached to the elevated portion  43   a  such that each top segment  44   a  is substantially parallel to one another as is required for proper operation. Each side stringer  54   a  is attached to either elevated portion  43   a  or base portion  48   a.  Similarly, each base stringer  56   a  is attached to the outermost ends of each base portion  48   a.    
     The first embodiment of the support structure  12   a  may be fabricated from concrete reinforcing wire. Each top segment  44   a,  side segment  46   a,    46   a,  and bottom portion  48   a,    48   a,  may be formed from a single section of concrete reinforcing wire by bending such material into the desired generally U-shaped configuration. Then the top  52   a,  side  54   a  and base  56   a  stringers may be welded at their respective locations in order to from the support structure  12   a.    
     Referring now to FIGS. 4 and 6, a second embodiment of a wire mesh support structure  12   b  can also support slip tubes  14  and is formed from a plurality of top segments  44   b,  generally V-shaped side segments  46   b  and base portions  48   b  inter-connected together. As seen in FIG. 4, each end of the top segment  44   b  is connected to an apex of the V-shaped side segment  46   b  in order to elevate the top segment  44   b  and form elevated portion  43   b.  Each side segment  46   b  is then attached to the base portion  48   b.  Therefore, as seen in FIG. 4, the plurality of base portions  48   b  are attached to the plurality of side segments  46   b  such that the side segments  46   b  are connected in a linear fashion side-by-side. A respective top segment  44   b  provides support to the apex of each V-shaped side segment  46   b  and spacers  60   b  attached to base portions  48   b  midway between two adjacent side segments  46   b,    46   b.  The second embodiment of the support structure  12   b  can be formed by bending two, long segments of concrete reinforcing wire into two generally sawtooth configurations comprising base portions  48   b  and side segments  46   b.  Then both sawtooth configurations of reinforcement wire are attached, typically through a weld, to top segments  44   b  and spacers  60   b  to form support structure  12   b.    
     Each support structure  12   a  and  12   b  is configured to maintain a plurality of concrete dowel slip tubes  14  in a substantially parallel relationship to one another and parallel to a top surface  58  of concrete slab  42 . Additionally, the support structure  12   a  and  12   b  maintains the slip tubes in substantially coplanar relationship. Therefore, each top segment  44   a  or  44   b  is attached to a respective side segment  46   a  or  46   b  such that each top portion is in parallel alignment with each other. Additionally, side segments  46   a  and  46   b  are sized such that each respective top segment  44   a  or  44   b  is elevated above the ground  50  in the same plane. Therefore, each side segment  44   a  or  44   b  has a length of between about 2.5 inches to about 24.0 inches. Each top segment  44   a  or  44   b  is sized to receive the clip  32  of slip tube  14 . As such, the length of the top segment  44   a  or  44   b  is between about 6.0 inches to about 30.0 inches and are spaced along the support structure between about 6.0 to about 30.0 inches. 
     CONCRETE DOWEL SUPPORT FOOT 
     The concrete dowel placement apparatus  10  additionally comprises the support foot  18  as shown in FIGS. 3,  4  and  5 . The support foot  18  supports the extended end  40  of support dowel  16 . As seen in FIG. 5, the support foot  18  comprises a generally annular base portion  62  that supports a frustum shaped wall  64 . The wall  64  is provided with a plurality of openings  66  for access to the interior of the support foot  18  during pouring of concrete. Referring to FIGS. 4 and 5, the support foot  18  is sized and configured to receive the support dowel  16  in at least one of a plurality of dowel engagers  68  formed about a top of the base portion  62 . The dowel engagers  68  are sized with an interior diameter slightly smaller than the outside diameter of the support dowel  16  in order to frictionally engage the support dowel  16 . Therefore, an engager  68  can “snap” onto the extended end  40  of support dowel  16 . 
     PREFERRED PLACEMENT METHODOLOGY 
     Now having described the components of the concrete dowel placement apparatus  10 , the function and method of using each component will be explained. Reference to the first embodiment of the support structure  12   a  will be made herein, yet it will be recognized that the second embodiment of support structure  12   b  can be interchanged with the first embodiment in the following description of use. First, slip tubes  14  are attached to the top segments  44   a  of the support structure  12   a  via clip  32  as previously described. The slip tubes  14  are typically spaced about 6.0 to 30.0 inches between adjacent members. Therefore, the slip tubes  14  can be placed on top segments  44   a  in any spacing configuration that achieves the desired distance between themselves. As seen in FIG. 1, the slip tubes  14  are attached to every fourth top segment  44   a,  however in FIG. 4, the slip tubes  14  are attached to every top segment  44   b.    
     Next, the support structure  12   a  is positioned in the location where a sawcut  70  will be made in the monolithic concrete slab  42  after pouring and curing thereof. As seen in FIG. 3, the support structure  12   a  is placed upon the ground surface  50  that supports the concrete slab  42 . The base portions  48   a  are substantially flush with the surface  50  in order to prevent tripping of workmen during pouring of the concrete slab  42 . Next, The support structure  12   a  is positioned to place a central axis “A” of the slip tubes  14  perpendicular to where sawcut  70  will be made after pouring of the concrete. Additionally, the support structure  12   a  is positioned such that the central axis “A” of the slip tubes  14  is parallel to the top surface  58  of concrete slab  42  after pouring thereof. As will be recognized to those of ordinary skill in the art, it is also possible to position the support structure  12   a  on ground surface  50  before the slip tubes  14  are attached thereto. As such, once the support structure  12   a  is in proper position and location, the slip tubes  14  are attached to top segments  44   a  as needed. 
     Before the concrete slab  42  is poured, the concrete support dowels  16  are inserted within a respective slip tube  14 . As previously described above, the support structure  12   a  is configured to support the slip tubes  14  and support dowels  16  inserted therein in a substantially parallel and co-planar relationship to one another, and parallel to the top surface  58  of concrete slab  42 . The support dowels  16  are slidable within a respective slip tube  14  in order to provide lateral displacement of the concrete slab  42  as will be further explained below. The extended end  40  of dowel  16  projects outwardly from the slip tube  14  such that the support structure  12   a  may become imbalanced and tend to tip toward surface  50 . If this happens, then support foot  18  is attached to the extended end  40  of dowel  16  to provide additional support thereto. The support foot  18  has a height which coaxially aligns a central axis “B” of support dowel  16  with the central axis “A” of slip tube  14  when support dowel  16  is attached to a respective dowel engager  68  of foot  18 . The dowel  16  must be easily slidable within the slip tube  14  for proper operation. Therefore, the central axis “A” of slip tube  14  must be coaxially aligned with the central axis “B” of support dowel  16  in order to prevent binding of the dowel  16  within tube  14  which may be caused since the sheath  20  is slightly larger than the diameter of the support dowel  16 . Additionally, support foot  18  aligns axis “B” of support dowel  16  to axis “A” of slip tube  14  during pouring of the concrete because the weight of the concrete can cause the support dowel to bend and therefor bind on sheath  20 . The weight of the concrete being poured onto dowel  16  may further act as a lever arm to pop the clip  32  off of the top segment  44   a.  As such, the support foot  18  provides support to extended end  40  to maintain slip tube  14  in parallel alignment with top segment  44   a  and to prevent clip  32  from releasing. 
     After having placed the dowels  16  into respective slip tubes  14 , the concrete slab  42  is formed by pouring concrete around the support structure  12   a.  The concrete encapsulates the support structure  12   a,  the exposed portion of the support dowel  16  and the foot  18  (if used). Since the foot  18  is provided with openings  66  formed therein, the concrete is able to fully surround and encapsulate foot  18 . Therefore, foot  18  (if used) can remain in place after the concrete has cured. Typically, the height of the support structure  12   a  is chosen to position the support dowels  16  midway between the top surface  58  of concrete slab  42  and the supporting ground surface  50 . 
     After the concrete slab  42  has cured, the sawcut  70  is formed on the top surface  58  of concrete slab  42  by sawing the slab  42  with standard concrete construction techniques. The sawcut  70  is located perpendicular to the central axis “A” of the slip tubes  14 . Additionally, the sawcut  70  must be located at the junction where the support dowel  16  enters the slip tube  14  (i.e., near the open end  22  of sheath  20 ). Since the dowel  16  is longitudinally slidable within the slip tube  14 , the concrete slab  42  may be laterally displaced about sawcut  70 . The portion of the support dowel  16  extending within the slip tube  14  is allowed to move freely in a longitudinal direction, whereas the portion of the dowel  16  extending into the concrete slab  42  is frictionally retained therein. The closed end  24  of sheath  20  prevents the seepage of concrete thereinto such that the portion of dowel  16  within the slip tube  14  is freely slidable in a generally horizontal direction. Therefore, the sawcut  70  is placed at the junction between the dowel  16  and slip tube  14  since this is the location whereby the dowel  16  is freely slidable horizontally. However, the dowel  16  is not movable in a vertical direction within slab  42  because it is encapsulated by concrete or retained within slip tube  14 . Therefore, the dowel  16  can prevent buckling or angular displacement of concrete slab  34  in the area whereby dowel  16  is positioned. 
     The present invention accurately positions concrete support dowels  16  during the pouring of the monolithic concrete slab  42 . As such, the positioning and configuration of the slip tubes  14  can be easily and quickly changed by varying the size of slip tube  14  and corresponding concrete support dowel  16 , as well as the size of the slip tube support structure. Since it is preferable to fabricate both the first and second embodiments of the slip tube supporting structure (i.e., support structure  12   a  or  12   b ) from concrete reinforcing wire, the structures can be modified very quickly. For example, the length of the structures can be decreased by trimming the structures at a desired location. As such, the present invention provides an adaptable system for quickly and easily placing concrete support dowels  16  before pouring a concrete slab  42 . 
     Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art such as varying the configuration of the slip tube support structure  12   a  or  12   b  as well as other configurations for the clip  32  of slip tube  14 . Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices within the spirit and scope of the invention.