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RELATED APPLICATION 
     This application is based upon and claims the benefit of Provisional Application 61/135,070, filed Jul. 15, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a dual anchor assembly for embedment in concrete slabs and to a lifting shackle adapted to simultaneously engage the multiple anchors of the assembly. In its more particular aspects, the invention is concerned with a void former which provides for positioning and placement of the anchors and forms an arcuate recess in the slab in intersecting relationship with the anchors. It is also concerned with an anchor assembly and hoisting shackle of increased load capacity, as compared to existing assemblies and shackles which employ single anchors. 
     2. Description of the Prior Art 
     The prior art relating to the present invention is typified by U.S. Pat. Nos. 3,883,170 and 4,367,892. These patents show single anchor assemblies for embedment in concrete slabs and associated releasable lifting shackles for engagement with the anchors. They also teach the provision of an arcuate recess around the end of the anchor engaged by the shackle. The &#39;892 patent, in particular, teaches a void former for forming the recess and placing the anchor. 
     It is also known in the prior art to provide anchor assemblies for embedment in concrete slabs, wherein the anchors have divergent portions to spread the load and resist pullout. Such a device, for use with a releasable lifting shackle, may be since in U.S. Pat. No. 4,173,856. In the device of that patent, however, each shackle engages only a single anchor. 
     SUMMARY OF THE INVENTION 
     The hoisting shackle of the invention comprises a ring-shaped body having a hollow toroidal portion with slots extending thereacross at spaced locations and an arcuate locking bolt slidably received within the toroidal portion for select extension across the slots and through anchors received within the slots. 
     The invention also provides an anchor assembly for embedment within a concrete slab to place a pair of anchors within the slab and form a void therearound. 
     The anchor assembly comprises a void former having a generally arcuate lower surface. At least two grooves are formed in and opening through the arcuate surface in annually spaced relationship to one another. Anchors are received within the grooves and extend laterally from the void former. Internally of the void former, the anchors provide annually aligned openings. 
     The concrete structure and lifting mechanism of the invention provide an arcuate recess within the concrete structure, a pair of anchors embedded within the structure and extending into the recess, and a releasable shackle complimentally received within the recess and engaged with the anchors. 
     The invention also provides a method for lifting a concrete structure wherein two or more anchors are embedded within the structure in divergent relationship and a ring-shaped lifting shackle is simultaneously engaged with the anchors. 
     A principal object of the invention is to provide an increased load capacity hoisting shackle having a quick release mechanism engagable with two or more anchoring elements embedded within a concrete structure. 
     Another and related object is to provide such a hoisting shackle which is not larger than existing shackles used with single anchoring elements. 
     Still another object of the invention is to provide a hoisting shackle and anchor combination for use in lifting concrete structures, wherein the load is divided into two parts to reduce the stress level within the shackle. 
     Yet another object of the invention is to provide an improved lifting anchor system for use in a relatively shallow concrete structure, which provides a wider spread of lifting forces within the structure. 
     A further object of the invention is to provide an anchor system for use in relatively a narrow concrete wall, which provides a wider spread of forces when pulled in the plane of the wall. 
     Another object of the invention is to provide the anchor system for use in narrow walls, wherein lifting forces are perpendicular to the plane of the wall and a wider lifting force sheer plate is provided within the wall. 
     Another object is to provide an anchoring system and lifting shackle for use in a deep mass concrete structure, which spreads the overall stresses within the structure and reduces the stresses within the shackle. 
     These and other objects will become more apparent from the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of the prior art lifting shackle of U.S. Pat. No. 3,883,170, showing the single anchor with which the shackle is used embedded within a concrete structure; 
         FIG. 2  is an elevational view of the lifting shackle of the present invention and the associated dual anchor embedded within a concrete structure; 
         FIG. 3  is a cross-sectional elevational view of the lifting shackle shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of the void former of the invention, with bar anchors shown in place within the void former; 
         FIG. 5  is an elevational view of one of the bar anchors shown in  FIG. 3 ; 
         FIG. 6  is a perspective view of the void former, without anchors in place; 
         FIG. 7  is a plan view of a pair of wire anchors positioned relative to one another, as they would appear in practice of the present invention; 
         FIG. 8  is a side elevational view of the anchor shown in  FIG. 7 ; and 
         FIG. 9  is a front elevational view of one of the anchors shown in  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates the prior art releasable lifting shackle of U.S. Pat. No. 3,883,170. The shackle comprises a cast steel shackle body  10  having a hollow toroidal cavity formed therein which carries an arcuate locking bolt  12 . The bottom of the shackle body  10  is formed with a slot  14  for receipt of an apertured anchor  16  embedded in a concrete structure  18 . A generally arcuate recess  20  is formed in the concrete structure around the anchor  16 . 
     In operation, the anchor  16  is received within the slot  14 , with the bolt  12  removed from the slot, and the bolt is then extended across the slot and through an aperture  22  formed in the anchor  16 . In this condition, the shackle is securely engaged with the anchor  16  and lifting force may be imparted to the concrete structure through the shackle. 
     The shackle of the present invention in seen in  FIGS. 2 and 3  wherein the steel shackle body is designated, in its entirety, by the numeral  24 . The body  24  has an annular cavity  26  which is open to the outside in the upper half of the body. The upper half of the body is thus an open U-shaped cross-section. The bottom of the body is of a closed U-shaped configuration and formed with a pair of generally trapezoidal slots  28  and  30  extending thereacross. Slot  28  has a vertical wall  32  and an outwardly divergent wall  34 . Slot  30 , similarly has a vertical wall  36  and an outwardly divergent wall  38 . This arrangement enables the shackle to move vertically into engagement with a pair of anchors  40 ,  42  cast in place within an arcuate recess  44  formed in the concrete structure  46  to be lifted. Such movement can be appreciated from a comparison of  FIGS. 2 and 3  wherein, in  FIG. 2 , the shackle is above the recess and in  FIG. 3  is received within the recess. A support section  33 , forming an integral part of the shackle body, is disposed between the slots  28 . A throughbore  35  extends fully through and across the section  33 . 
     The angle of the divergent walls  34 ,  38  is chosen to compliment the angle at which the anchors  40 ,  42  are set. The preferred range of angles, as measured from vertical, is between 10 and 35 degrees. When the anchors are received within the slots, the outer surfaces of the anchors engage the divergent surfaces. Complimental engagement of the anchors with the shackle also occurs through means of sockets  48  formed in the shackle body at the ends of the slots  28 ,  30 . These sockets are of a generally trapezoidal configuration corresponding to that of the ends of the anchors  40 ,  42 . 
     The anchors  40 ,  42  are of identical configuration and are of each “bar” type. Their configuration can best be appreciated from  FIG. 5  where it will be seen that each anchor comprises:
         an elongate body  50 ;   a convergent/divergent proximal portion  52 ;   a foot  54 ; and   a distal portion  56  having an elongate aperture  58  formed there through.
 
The top of the distal portion  56  has a flat upper surface  60  and tapered side surfaces  62 . The upper surface  60  and side surfaces  62  form a generally trapezoidal configuration generally complimental to the sockets  48  formed in the shackle body  24 .
       

     The basic structure of the inventive shackle is completed by an arcuate locking bolt  64  slidably received within the shackle body  24  for movement between the open condition shown in  FIG. 2  and the closed condition shown in  FIG. 3 . The bolt extends through approximately 180° of the circumference of the shackle body and, when unloaded, is freely movable therein. The throughbore  35  is of an arcuate configuration complimental to that of the bolt  64  and so proportioned and positioned as to enable the bolt to extend freely therethrough, when unloaded. When loaded, lifting forces imparted to the bolt by anchors  40 ,  42  are transmitted to and carried by the lower interior surface of the throughbore  35  and the lower interior surfaces of annular cavity  26 . A handle  66  extends through the open slotted top of the shackle body to enable the bolt to be manually moved between the open and closed conditions. 
     As shown in  FIG. 2 , a closed link  68  extends through a generally centrally disposed opening  70  formed through the shackled body  24 . The link would be secured to a lifting hoist (not illustrated). 
     The operation of the lifting shackle can be appreciated from a comparison of  FIGS. 2 and 3 . In  FIG. 2 , the shackle is about to be lowered into receiving engagement with a pair of anchors embedded within the concrete structure. During this lowering process, the vertical walls  32 ,  36  of the shackle body pass between the anchors  40 ,  42 . Ultimately, the ends of the anchors complimentally nest within the sockets  48  and the outer surfaces of the anchors complimentally engage the divergent walls  34 ,  38  of the shackle body. The later condition is shown in  FIG. 3 . 
     Once the shackle body is fully engaged over the anchors, the locking bolt  64  is moved annularly within the body and extended through the throughbore  35  of the section  33  and the apertures  58  of the anchors, as shown in  FIG. 3 . This serves to both secure the shackle to the anchors and to maintain the outer surface of the shackle in complimental engagement with the inner surface of the arcuate recess  44 . 
       FIG. 4  shows a void former  72  for positioning the anchors  40 ,  42  within a concrete structure, as the structure is being formed, and creating an arcuate recess within the surface of the structure. The void former  72  is fabricated from a relatively strong resilient material, such as rubber or polymer. The lower surface  74  of the void former is of arcuate configuration corresponding to that of the recess  44  to be formed within the concrete structure. The upper surface  76  is generally flat and may have a recess formed therein for the attachment of placement hardware. Grooves  78  extend the cross and open through the lower surface  74  of the void former, for receipt of the anchors  40 ,  42 . These grooves are proportioned for snug receipt of the anchors and are disposed to position the anchors at the desired inclination within the body of the concrete structure being formed. Protrusions  80  within the grooves  78  are provided for engagement with the apertures  58  of the anchors. 
     In use, the void former is positioned within the form for the concrete structure and concrete is then poured around the void former and anchors, to the level of the upper surface  76  of the void former. Removable pedestals (not illustrated) may be secured to the feet  54  to support the anchors. Once the concrete has sufficiently cured, the void former is removed, thus leaving an annular  44  recess formed in the surface of the concrete structure, with the anchors  40 ,  42  extending into the recess. 
       FIGS. 7 to 9  illustrate an alternative pair of anchors which may be used in place of the anchors  40 ,  42 . These alternative anchors are made of bar or wire stock and are particularly well adapted for use in relatively thin concrete slabs to better spread lifting loads through the mass of the concrete. Each anchor, designated  82 , is of a generally v-shaped configuration having a pair of divergent legs  84  defining a clevis  86  at their joinder. The legs terminate in inwardly bent distal ends  88 . 
     The preferred dimensions and angles of divergence for the anchors  82 , when placed within a concrete slab, are shown in  FIGS. 8 and 9 . These dimensions and angles, together with the provision of the inwardly extending distal ends  88 , provide for optimum resistance to pull out by maintaining a large body of concrete under compression, as lifting forces are applied to the anchors. 
     In use, the anchors  82  are positioned relative to the lifting shackle in essentially the same relationship shown in  FIGS. 2 and 3 , with regard to the anchors  40 ,  42 . The principal difference is the inward surfaces of the devises  86  provide the apertures through which the locking bolt  64  is extended. Void formers, similar to that of  FIGS. 4 and 6 , may be provided for initial placement of the anchors  82 . 
     CONCLUSION 
     From the foregoing description, it should be apparent that the present invention provides for the attainment of the objects initially set forth herein. In particular, it provides a dual anchor lifting shackle and an improved apparatus and method for placing multiple anchors within a concrete structure and lifting the structure through a common shackle simultaneously engagable with the anchors. It should be understood, however, that the invention is not limited to the specifics which have been described and illustrated, but rather is defined by the accompanying claims.

Summary:
A lifting mechanism for a concrete structure is provided through means of a void former and anchor assembly which it cast in place to provide an accurate recess in the structure having two or more spaced divergent anchors therein. The anchors define annularly aligned apertures within the recess. A lifting shackle of an arcuate configuration complimental with that of the recess is received within the recess and carries an arcuate locking bolt extendable through the aligned apertures.