Abstract:
A concrete weldment has a central plate with shear force reinforcing members at both ends of the central plate. There is a pair of outstanding arms extending out from each of the ends of the shear reinforcing members. The shear reinforcing members are twisted approximately 45° so that the outstanding arms are rotated substantially 45°. This rotation preserves the vertical and horizontal shear capacity of the weldment as well as to keep the slab reinforcement means well protected with proper concrete coverage. Each of the outstanding arms has a 90 degree bend at the ends for providing increased pull out tensile capacity of the weldment.

Description:
FIELD OF THE INVENTION 
     This invention relates to a metal weldable piece that is embedded into a thin concrete slab type structure and the method of manufacturing the slab so that the weldable piece is properly positioned in the slab. The weldable piece is used to join adjacent concrete structures or slabs by welding together the weldable piece embedded in each of the concrete structures. 
     More specifically, the invention is directed to:
         (1) Connecting “THIN SLAB” (three inches or less) precast structure only. It is not practical to use this type of weldment for slab thickness exceeding 3 inches.   (2) Twisting of both arms for 45 degree for providing room for concrete coverage of the reinforcement and maintaining the vertical shear capacity of the connection.   (3) A central plate having a 30 degree angle out of vertical to provide an easier orientation for field welding.   (4) Automatic stamping and the minimizing of material waste to provide the manufacturing by most economical manufacture product.       

     BACKGROUND AND SUMMARY OF THE INVENTION 
     Precast thin concrete slab type structures are commonly used in constructing roof, floors, and concrete decks. They generally take the shape of concrete slabs which may have a t-shape in cross section. There is a horizontal portion of the slab which is the load bearing surface and there is generally reinforcing mesh or bars within the slab. There is at least one generally flat surface or edge that adjoins a flat surface or edge of a confronting adjacent slab. The top surface of the slab is usually kept rough to be ready to receive a cast in place composite concrete topping with topping reinforcements which is a minimum 2 inches thick. 
     When the concrete slabs are placed next to each other to form the deck, it is possible for the slabs to move with respect to each other. This is due to construction loading, wind forces or thermal expansion. In order to prevent or minimize the relative movement and to increase the strength of the final structure, metal inserts, often called “weldments” are placed within the concrete slabs with a portion of the weldment extending out from an edge of the slab. When the slabs are positioned for final assembly, the metal weldment of one slab is aligned with and opposite to a complementary metal weldment in an adjacent slab (see  FIGS. 7 and 8 ). The complementary metal weldments are welded to each other to join the two weldments. This results in a unitary structure that is much stronger and less prone to movement than if no means of joining the slabs were used. While designing the connection and the weldment, the following aspects are considered:
         (A) horizontal shear capacity (Vh) to provide the diaphragm force,   (B) tensile capacity (T),   (C) vertical shear force (Vv) to resist the uneven loading between adjacent slabs,   (D) concrete coverage of slab reinforcement to be maintained before the topping is installed in the field,   (E) ease of placement of the loose welding steel and ease of welding, and   (F) overall material cost.       

     Various types of weldments have been used in the past. Once such type which has been used is illustrated in U.S. Publication No. 2003/0140590 to Lancelott, III et al. This is a U-shaped thin steel plate that had two arms of the “U” embedded within the concrete and the base of the “U” exposed along the edge of the concrete slab. Due to its pointing shape, the arms often are pulled out from the slab when under tensile load. This is unacceptable as it substantially weakens the overall structure. 
     Another weldment which has been used is illustrated in U.S. Pat. No. 5,402,616. This type of weldment solved some problems except its vertical arms are deep which sacrifices the concrete coverage above the slab reinforcement especially when the total slab thickness is thin. This type of weldment is very helpful for thick slabs that have sufficient space to provide concrete coverage above the slab reinforcement, but it provides unacceptable coverage for thinner slab structure. 
     Another weldment is illustrated in U.S. Pat. No. 6,854,232. The vertical arms of this type of weldment are rotated almost 90 degree to make room for the weldment, slab reinforcement and its concrete coverage. A major problem with this weldment is that at the extreme degree bend location, a hinge point is created which reduces the vertical shear capacity of the weldment and creates localized spall beneath or above the weldment. This reduces the strength of the weldment. 
     Thus, there is the need for a concrete weldment having improved securing properties over the weldments illustrated in the prior art that results in the weldment being more securely retained within the thin concrete slab with proper slab reinforcement&#39;s concrete coverage, even when the weldment is subjected to vertical and horizontal forces. Applicant&#39;s invention provides an increased weldable area, at the proper angle to the concrete surface for easier welding proposes, and allows for thermal expansion of the weldment without cracking and spalling the concrete. 
     Applicant&#39;s invention solves the problems stated above by providing a weldment that comprises a central plate which defines the weldable surface. The central plate is at approximately 30 degree angle with respect to the vertical edge of the concrete slab which solves the problems of providing an easily accessible weldable surface. There are shear force reinforcing members at both ends of the central plate. The reinforcing members are designed to minimize the twisting length in order to avoid interfering with the slab reinforcement mesh or reinforcing bars that are placed in the slab. The maximum amount of twisting or rotation is limited to 45 degree in order to preserve the vertical and horizontal shear capacity as well as to keep the slab reinforcement means well protected with proper concrete coverage. There is a pair of outstanding arms extending out from each of the ends of the shear reinforcing members. Each of the outstanding arms has a 90 degree bend at the ends of the arms which provide for increased pull out tensile capacity of the weldment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is top plan view of the inventive weldment. 
         FIG. 2  is a front elevation view of the weldment shown in  FIG. 1 , 
         FIG. 3  is a right side elevation view of the weldment. 
         FIG. 4  is a front perspective view of the weldment. 
         FIG. 5  is a rear perspective view of the weldment. 
         FIG. 6  illustrates the blank weldment after it is stamped and before it is bent and twisted into the final form. 
         FIG. 7  is a perspective view of two concrete slabs each having a weldment embedded within, with the exterior face of the central plates facing each other. 
         FIG. 8  is a section view with portions removed of two adjacent concrete slabs illustrating the position of the weldments in each slab with respect to each other. 
         FIG. 9  is section view of the mold used for forming the concrete slab with the weldment and slab reinforcement placed in the mold. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning first to  FIG. 1 , there is illustrated a weldment  10  of the present invention. The weldment  10  is designed to be embedded in a thin concrete slab-type structural member  12  (hereinafter referred to as “concrete slabs”), generally having a thickness of no more than three inches. The concrete slabs are designed to have an extended length as compared to its width. The concrete slabs  12  are positioned so that edges  14  of adjacent concrete slabs  12  abut each other as seen in  FIGS. 7-9  to form a building element such as a deck surface. Several weldments  10  are placed at predetermined distances along the edge  14  of the concrete slabs  12 . Thus when the concrete slabs  12  are placed confronting each other, the weldments  10  are in alignment with weldments in the confronting concrete slab  12  and are in close proximity to each other so that the weldments  10  can be welded together thereby increasing the overall strength of the deck surface. The horizontal shear capacity of the weldment  10  will provide the shear requirement to make the concrete slabs  12  act as one diaphragm after welded together. After the concrete slabs  12  are welded together to form the precast deck, a pour in place composite concrete topping is cast on top of the thin concrete slabs to support the final dead and live loads. During construction, the vertical shear capacity due to uneven loading of casting concrete is also carefully considered. 
     The design of the weldment  10  is most clearly illustrated in  FIGS. 1-6 . There is a central plate  16  having first and second ends  18  and  20  respectively. The weldment also has a height “H” and a length “L” that is greater than the height H. The height H is selected so that it is less than the thickness of the concrete slab  12 . The central plate  16  has a ⅜ inch chamfer  22 ,  24  at both ends  18 ,  20 . Beyond the first and second ends  18 ,  20  are shear force reinforcing members  26 ,  28  that provide a transition piece to attach the central plate  16  to right and left outstanding divergent arms  30  and  32  respectively. From the front view of  FIG. 2 , the right arm  30  is twisted clockwise and the left arm  32  is twisted counter clockwise 45° from a vertical or horizontal plane. The entire twisting is accomplished across the shear reinforcing members  26  and  28 . The purpose of the twisting of the arms  30  and  32  is to provide the proper amount of concrete coverage  34  above the arms  30  and  32  within the concrete slab  12  as seen in  FIG. 9 . 
     The twisting should not be so great that it results in a hinge effect which minimizes the strength of the weldment  10  at the point of twisting. This hinge effect is seen in U.S. Pat. No. 6,854,232 wherein the arms are rotated 90° (as seen in  FIG. 3  of U.S. Pat. No. 6,854,232) which results in the hinge effect when the concrete slabs are subjected to vertical shear. The design of the weldment in the &#39;232 patent greatly reduces the vertical shear capacity of the weldment  10  and causes concrete spall in the slab when the loading of two adjacent slabs are not even. 
     At the ends of the arms  30  and  32  are downwardly extending fingers  36 ,  38  that extend at substantially 90° from the divergent arms  30  and  32  respectively. The fingers  36 ,  38  assist in anchoring the weldment  10  in the concrete slab  12  and provides additional tensile strength capacity. 
     The central plate  16 , shear force reinforcing member  26 ,  28 , right and left divergent arms  30 ,  32  and fingers  36 , 38  are all manufactured from one piece of metal, preferable a high strength steel. Thus the central plate, reinforcing members, divergent arms and fingers are all integral with each other giving substantial strength to the weldment  10 . The 45° twist of the divergent arms being spread across the shear force reinforcing member  26 ,  28  provides increased vertical and horizontal shear capacity over the weldments of the prior art. 
     The method of manufacturing the concrete slab  12  is best illustrated in  FIG. 9 . A mold or steel form  40  is used to form the slab  12 . The mold  40  has a bottom  42  and side walls  44  which define the bottom and edges of the length and width of the thin concrete slab  12 . Mesh  46  is placed in the form  40  and is mounted at the correct height to provide proper coverage of the mesh  46  and weldment  10 . The weldment  10  is attached to the bottom of the mesh  46 . This secures the arms  30 ,  32  to the mesh  44  such that the arms  30 ,  32  are horizontally parallel to the bottom  42  of the mold  40  and therefore horizontally parallel to the finished slab  12 . This results in the surface of the central plate  16  being at approximately a 30° angle from the vertical plane of the vertical side wall  44 . This design facilitates field welding of a weld plate  48  ( FIG. 7 ) between adjacent confronting weldments  10 . 
     Once the weldment  10  is properly positioned within the mold  40  as described above, concrete is poured into the mold  40  to the proper depth of the concrete slab. It is preferable for the top edge of central plate  16  to be flush with or slightly below the top of the concrete slab  12 . To keep the exterior surface of the central plate  16  clean and suitable for welding, a temporary wedge type plastic or wood mold  49  can be inserted in the mold  40  and used to keep wet concrete off the central plate surface. 
     Turning to  FIG. 8 , there are illustrated two concrete slabs  12  in face to face orientation. Each slab  12  has at least one weldment  10  embedded within the slab  12 . The central plate  16  of each weldment  10  faces the other. With the two slabs  12  slightly separated by approximately ¼ inches, the welding plate  48  is placed between the two central plates  16 . With the 30° tilt of the central plates  16 , it is convenient to place the welding plate  48  into the V shaped notch formed by the two tilted central plates  16  and do the welding so that a unitary structure is created by the two central plates  16 , the welding plate  48  and the field weld. This V shaped notch will be filled with concrete during the topping pouring operation. 
       FIG. 7  is similar to  FIG. 8  except it is a perspective view with portions removed illustrating the position of the weldments  10  when the two concrete slabs  12  are facing each other. The welding plate  48  is positioned between the two slabs  12  and supported by the central plate  16 . Once the field weld is made, the two concrete slabs  12  act as one unitary structure. It resists horizontal shear, vertical shear and tensile forces in both directions as illustrated by arrows Vh, Vv and T. 
     The weldments  10  can be manufactured from steel blanks stamped from sheets. By properly laying out the stamping of the blank weldments as shown on  FIG. 6 , the use of the steel material can be maximized and the waste material minimized. Once the blank weldments have been punched, they can be formed by standard metal bending operations and no additional parts must be added to the weldment to complete the finished piece. 
     Thus there has been provided a concrete weldment that fully satisfies the objects and advantages set forth above. While the invention has been described in conjunction with a specific embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.