Patent Publication Number: US-8109691-B2

Title: Apparatus and method for on site pouring of pre-stressed concrete structures

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to apparatus for pouring pre-stressed concrete, used for roadways, walls, and structural beams and supports. More specifically, the invention pertains to and apparatus and a method, for pouring pre-stressed concrete structures in situ, through the use of a transportable cable stressing frame, positioned and maintained directly over a form for the concrete structure. 
     2. Description of the Prior Art 
     Pre-stressing concrete has long been recognized as a technique to increase the tensile strength of cast concrete structures. The method generally requires that high strength wires, cables, or rods, passing through the empty mold or form for the concrete structure, are pre-stressed under high tension using a calibrated tensioning fixture. Then, the concrete is poured into the mold or form, enveloping the pre-stressed wires or cables. After the concrete has cured, the wires outside the mold are cut from the tensioning fixture, transferring the compressive forces to the concrete through the bond between the wires or cables and the concrete. 
     The general principles of this technique are illustrated in U.S. Pat. No. 6,773,650, issued to Longo for a Prestressed Concrete Casting Apparatus And Method. The &#39;650 patent illustrates a pre-stressing clamshell apparatus designed to cast cementitious power poles. In this arrangement, a plurality of stationary, cable pre-tensioning devices are lined up at a production facility. The movable clamshell mold surrounds each pre-tensioning fixture while the concrete is poured and allowed to set. Then, the mold is opened and lifted up, and then moved along to the adjacent fixture, where the process is repeated. 
     An Apparatus For Making Prestressed Structural Members is disclosed in U.S. Pat. No. 3,049,786, granted to Jones. This apparatus uses a cable pre-stressing fixture like that shown in the &#39;650 patent, but relies upon a movable mold member  60 . As concrete is poured into the mold member, the mold member is slid along the fixture until the entire poured structure is formed over the cables. 
     In U.S. Pat. No. 3,260,024, issued to Greulich, a Prestressed Girder is shown. This reference suggests that the girder can be constructed either at the prestressing plant or at the building site, using an apparatus such as that depicted in  FIG. 1 . A horizontal beam  3  includes jacks  1  mounted on opposing anchor members  2 . The concrete pour is made over the cables and the underlying beam. There is no particular adaptation or suggestion how this apparatus might be used in the field, for example at a building site, other than simply transporting the same apparatus that is used at the prestressing plant to the building site. 
     Basically the same methods discussed above are used to manufacture pre-stressed concrete slabs or roadway segments. These concrete structures are used for new road construction, or for purposes of road repair. For example, in making a new freeway, or in repairing damaged portions of roadway, a concrete slab or roadway segment is manufactured at an off-site facility, using a cable pre-stressing apparatus and a form or mold arrangement associated with that apparatus. After the concrete is poured and cured, the slab is transported by truck or rail to the roadway site for installation. In preparing a bed within which the new slab is to rest, every effort is made to match the inclination, orientation, and depth of the bed with that of the new slab, so that a smooth roadway transition can be made between adjacent slabs. Notwithstanding these efforts, it is very difficult to effect a perfect match between the bed and the slab, and surface anomalies and gaps do occur between adjacent slabs. 
     Similarly, it is conventional that pre-stressed walls, beams, posts, and other concrete structures are manufactured at a production facility, where permanent fixtures are located for pre-stressing cables and forms are provided to determine the size and configuration of the concrete structures. As with the roadway slabs, after pouring and curing, these concrete structures must also be transported to a remote building site, offloaded, and assembled or arranged as required. 
     SUMMARY OF THE INVENTION 
     The apparatus and method disclosed herein are specially adapted to manufacture pre-stressed concrete structures, such as roadway segments, precisely at the site where the pre-stressed structure is to be used. Additionally, for other concrete structures, such as walls, beams, posts, and the like, production takes place at the same location where place of assembly or installation occurs. 
     This is accomplished by providing a transportable pre-stressing frame which is readily moved from pour site to pour site. This feature is useful, for example, when making interconnected roadway segments, arranged end-to-end, for a freeway. Transport of the pre-stressing frame from site to site can also be advantageous, where the building site is large or there is need for production of building components for multiple buildings in the same general area. 
     In contrast to prior art devices which generally employ a permanently mounted beam or frame on the floor of a manufacturing facility, the present device has a transportable pre-stressing frame, provided with downwardly directed outrigger assemblies at either end of the frame. The frame is initially positioned and then maintained in horizontal, spaced relation, above a form at a pour site, using adjustable mechanical, hydraulic, or electric jacks, or other equivalent raising and lowering devices. The form is typically comprised of opposing side structures or walls, spanned by opposing bulkheads at either end of the form. The length of the frame is such that each of the outrigger assemblies is located outside the form, adjacent a respective bulkhead. 
     Cables are secured to the outrigger assemblies at one end of the frame, and passed through the bulkheads to corresponding outrigger assemblies at the other end of the frame. The elevation of the cables is maintained below the upper edge of the form. Preferably, the cables are located mid-way between the floor of the form and upper edge. Each of the cables is pre-stressed to a predetermined tension, using conventional cable pre-stressing fixtures. With the form ready and the cables pre-stressed, concrete is poured into the form entirely covering the cables. With accelerators and other additives, concrete can be cured sufficiently in a number of hours, so that the tension forces in the cables can be released and transferred to the concrete slab as compressive forces. This is accomplished by cutting the cables at a point just past each end of the formed concrete slab, in a region between the outriggers and the bulkheads. The bulkheads are of split design, allowing their removal from around the cable and the end of the slab. The pre-stressing frame can then be lifted and removed from the site, and relocated to a new site. 
     Successive pours of slabs can be made, in end-to-end relation, to form a continuous roadway made from pre-stressed concrete poured on the site. Adjacent slabs are perfectly aligned, as the height of each form is readily adjusted to match the height of the adjacent slab, and the orientation and horizontal position of the form are likewise adjustable at the pour site. 
     The same apparatus and method can be used to manufacture walls, beams, posts, and poles on site, very near to where the concrete structure is eventually installed and utilized. Transportation costs and possible damage to the structures are reduced, as the structures do not have to be moved from a manufacturing facility. Lastly, the transportable frame can quickly be moved from construction site to construction site, as needed, improving the efficiency and speed of manufacturing and assembling concrete structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pre-stressing frame fitted with a plurality of outriggers and associated cables, a secondary outrigger frame being shown in alternate positions along the frame side rails; 
         FIG. 2  is a top plan view of the pre-stressing frame of  FIG. 1 ; 
         FIG. 3  is a side elevational view of the pre-stressing frame of  FIG. 1 ; 
         FIG. 4  is an end elevational view of the pre-stressing frame of  FIG. 1 , showing a plurality of outriggers and the adjustable support jacks; 
         FIG. 5  is a fragmentary perspective view of one end of the pre-stressing frame; 
         FIG. 6  is an exploded perspective view of an outrigger, showing a receiver and a cable restraint extension; 
         FIG. 7  is an exploded perspective view taken from a low angle, showing the outrigger assemblies used on the secondary outrigger frame; 
         FIG. 8  is a side elevational view of a cable restraint extension, showing the chuck recess and cable passageway in broken line; 
         FIG. 9  is an end elevational view of a cable restraint extension, showing the chuck recess; 
         FIG. 10  is a perspective view of a typical structural form for a concrete roadway segment; 
         FIG. 11  is a fragmentary perspective view showing the split bulkheads used in the form of  FIG. 10 ; 
         FIG. 12  is a fragmentary, exploded, perspective view of a split bulkhead, showing the upper plate and the lower plate and a pair of cables in phantom line; 
         FIG. 13  is a cross-sectional view taken on the line  13 - 13 , in  FIG. 11 ; 
         FIG. 14  is an exploded perspective view of a pour site for a roadway segment, showing the form, the cables, and the overlying pre-stressing frame; 
         FIG. 15  is a top plan view of a roadway segment, after it has been poured in contingent relation to the end of an existing roadway; 
         FIG. 16  is a fragmentary perspective view of the end of the pre-stressing frame, showing the cable pre-stressing fixture, a cable undergoing pre-stressing, and a locking chuck; 
         FIG. 17  is a fragmentary, side elevational view of an end of the pre-stressing frame, showing an outrigger assembly fitted with a pre-stressed cable, a portion of the jack and the bulkhead being broken away for clarity; 
         FIG. 18  is a perspective view of the pre-stressing frame and pre-stressed cables positioned over a form, showing the process of covering the cables with concrete and filling the form to an upper grade level at the top edge of the form; 
         FIG. 19  is a side elevational view showing the pre-stressing frame and form of  FIG. 18 , prior to pre-stressing the cables; 
         FIG. 20  is a side elevational view as in  FIG. 19 , after the cables have been pre-stressed with the pre-stressing frame bowed slightly upward under the stress; 
         FIG. 21  is a perspective view of a roadway repair site, showing the cutout portion of the roadway, the bulkheads, and the pre-stressing frame; 
         FIG. 22  is a top plan view, showing the roadway of  FIG. 21 , after repair; 
         FIG. 23  is a perspective view as in  FIG. 21 , but showing the bulkheads and the pre-stressing frame installed in the cutout portion of the roadway; 
         FIG. 24  is a side elevational view of the pre-stressing frame used in conjunction with the secondary frame, in preparation for the pour of a short roadway segment; 
         FIG. 25  is a perspective view of a repaired roadway, showing expansion joints at each end of the roadway repair segment; 
         FIG. 26  is a cross-sectional view, taken on the line  26 - 26 , shown in  FIG. 25 ; 
         FIG. 27  is a side elevational view, showing two pre-stressing frames in end-to-end relation, configured to form a new roadway; 
         FIG. 28  is a top plan view of a roadway, showing adjacent newly poured roadway segments and the gaps therebetween forming expansion joints; 
         FIG. 29  is a cross-sectional detail view, taken on the line  29 - 29  in  FIG. 28 ; 
         FIG. 30  is a cross-sectional detail view, taken on the line  30 - 30  in  FIG. 28 ; 
         FIG. 31  is a fragmentary, exploded, perspective view of an end of an “I” beam pre-stressing frame in combination with a structural form for making pre-stressed concrete beams or posts; 
         FIG. 32  is a fragmentary, perspective view of the pre-stressing frame of  FIG. 31  fitted with pre-stressed cables, shown in nested, overlying relation with the form; and, 
         FIG. 33  is a fragmentary, perspective view of the pre-stressed beam or post, manufactured from the apparatus shown in  FIG. 32 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, the apparatus  11  of the present invention includes an elongated cable pre-stressing frame  12 , having a first end  13  and a second end  14 . At least one first outrigger assembly  16  depends from the first end  13 , and at least one second outrigger assembly  17  depends from the second end  14 . In a typical setting, such as that shown in  FIG. 1 , a plurality of identical outrigger assemblies  16  and  17  are utilized at each end of frame  12 . 
     As shown more particularly in  FIGS. 5-9 , each outrigger assembly  16  and  17  comprises a receiver  18  and a cable restraint extension  19 . A chuck recess  20  is provided in the lower end of extension  19 . Receiver  18  includes a slot portion  21  sized and configured to accept a tongue portion  22  of cable restraint extension  19 . Removable pins  23  are provided selectively to secure cable restraint extension  19  within receiver  18 . The upper end of receiver  18  is provided with an L-shaped bracket  24 . The ends of frame  12  are provided with a length of angle iron  26 , having an upper side arranged in spaced relation from the upper side of frame  12 . A slot is thereby formed, so that a portion of bracket  24  can be slid within the slot, allowing outrigger assemblies to be mounted in the desired number and location along the end of frame  12 . 
     In a preferred embodiment, frame  12  includes elongated side rails  27 , arranged in parallel spaced relation, and transverse end rails  28  and  29 . This construction provides a very strong structure against which the pre-stressed cables, discussed below, can be tensioned to predetermined specifications for manufacturing pre-stressed concrete structures. This construction also allows the frame  12  to be disassembled into a more compact configuration, in the event the side rails are provided with telescoping sleeve portions, suggested by joint lines  31 . It may be desirable for manufacturing more narrow concrete structures, such as beams and posts, to fabricate frame  12  from a single I-Beam  32  fitted with transverse end rails  28  and  30 . This alternative construction is shown in  FIGS. 32 and 32  and will be discussed in more detail below. 
     As illustrated in  FIG. 10 , the apparatus  11  also includes a form  33  which defines the shape and size of the concrete structure to be manufactured. Generally, form  33  has opposing elongated sides  34 , and opposing first and second transverse bulkheads  36  and  37 . However, the form can assume any desired geometric or irregular shape and size which is required for the application. It should be noted that form  33  has an upper edge  38  which defines the upper surface for the concrete structure to be manufactured using apparatus  11 . In the event the apparatus  11  is being used to create a new roadway segment  39 , the upper edge  38  lies in the same plane as adjacent roadway segments to create a smooth transition between adjacent roadway segments. In preparation, the floor surface surrounded by form  33  is typically graded as needed. The floor may also be covered with one or more layers of substrate material to form a bed for the pour. 
     Form sides  34  may be constructed from reinforced metal plates, wooden planks or the like, of conventional design. Since roadway segments  39  can extend up to 60′ or so in length, it may be desirable to assemble sides  34  from a number of modular units (not shown), so as to make handling easier. On the other hand, breaking up sides  34  into a plurality of such units would require more labor to assemble and disassemble the apparatus when moving from pouring site to pouring site. 
     Bulkheads  36  and  37  are of split design, primarily to facilitate the passage of at least one pre-stressed cable  41  through the middle portion of each bulkhead. Making particular reference to  FIGS. 12 and 13 , each split bulkhead  36  and  37  comprises an upper plate  42  and a lower plate  43 . Upper plate  42  includes at least one cutout  44  in a lower flange portion  46 , allowing the passage of cable  41  therethrough. It is evident that the flange and the cutout provided on the upper plate could alternatively be placed on the lower plate with the same result. Spacer blocks  47  provide a sufficient gap between the lower side of plate  42  and the upper side of plate  43 , to allow passage of cable  41  between the two plates. The plates are detachably affixed to each other by means of nuts  48  and bolts  49 , to make assembly and disassembly of the bulkheads a relatively quick process. As is evident from  FIG. 13 , the inner sides of upper plate  42  and lower plate  43  provide a substantially planar surface for the inner ends of form  33 . 
     Although the apparatus  11  includes at least one pre-stressed cable  41 , the configuration of the apparatus shown in  FIG. 1  includes a plurality of such cables. Each cable  41  extends from a cable restraint extension  19  of the first outrigger assembly  16  to a respective cable restraint extension  19  of the second outrigger assembly  17 . In doing so, each cable  41  passes through cutouts  44  in first bulkhead  36  and in second bulkhead  37 , in the manner explained above. It may also be desirable to apply caulking or packing  51  (See,  FIG. 13 ), around each cable as it passes through the cutouts, to provide an adequate seal against leaks of the concrete to be poured. 
     Apparatus  11  further includes jack means  52 , for positioning and maintaining elongated frame  12  over, and generally in longitudinal alignment with, form  33 . Jack means  52  may be any conventional raising and lowering device, such as a mechanical, hydraulic, or electric jack. As shown in  FIGS. 14 and 18 , four such jacks  52  are used in most applications, two at each end of frame  12 . Each jack  52  is positioned on the ground, or other adjacent supporting surface outside form  33 . Then, frame  12  is properly oriented and lowered over form  33 , supported solely by the jacks and maintained in spaced relation from the form. Using the height adjusting capabilities of the jacks  52 , the elevation of the frame is set so that each of the pre-stressed cables  41  is lying below the upper edge  38  of form  33 . Preferably, each cable  41  is located approximately mid-way in height, between the upper edge  38  and the floor, or lower grade level within form  33 . 
     Each of the cables  41  is pre-stressed to a predetermined tension, by means of a conventional pre-stressing fixture  53 , shown in  FIG. 16 . Enerpac, having world headquarters in Milwaukee, Wis., makes a number of suitable pre-stressing fixtures for use with the apparatus  11 , including Models PTJ5S and 5DA1. Other examples of such fixtures include the PSI Hercules Stressing Systems stressing jacks, manufactured by Prestress Supply, Inc. located in Lakeland, Fla. Pre-stressing fixture  53  includes controls and gauges which determine the amount of tension to be placed upon each cable  41 . Typically, tension forces within the range of 20,000 lbs. to 40,000 lbs. are applied, in accordance with the engineering specification for the pre-stressed concrete to be manufactured on site. 
     As a first step in the cable pre-stressing process, a pre-stress chuck  54 , or other equivalent cable locking device, is engaged over one end of the cable  41 , adjacent the cable restraint extension  19 . The chuck  54  includes a forward nose portion that seats within chuck recess  20 , provided in the lower end of cable restraint extension  19 . Suitable pre-stress chucks include the Sure-Lock Splice Chuck and the Sure-Lock Strand Chuck, manufactured by MeadowBurke, located in Tampa, Fla. 
     Next, the pre-stressing fixture  53  is attached to the other end of the cable, adjacent a respective cable restraint extension  19 , as illustrated in  FIG. 16 . After the fixture has been actuated and the predetermined cable tension reached, another chuck  54  is engaged between the cable and the cable restraint extension  19 . This second chuck is effective to maintain the cable tension after the pre-stressing fixture is removed. After the second chuck  54  is locked in place, the pre-stressing fixture  53  can be removed from the tensioned cable, and relocated for attachment to any other cables remaining to be pre-stressed. In this manner, the plurality of cables  41  are pre-stressed to a predetermined tension, in preparation for the concrete pour. 
       FIGS. 19 and 20  depict the effects that cable pre-stressing has upon frame  12 . In  FIG. 19 , the cables  41  are extending between the outriggers  16  and  17 , but the cables have not yet been pre-stressed. In this state, frame  12  is linear in configuration, as suspended over form  33 . As shown in  FIG. 20 , however, the cables  41  have been pre-stressed using the pre-stressing fixture  53 , and it is evident that a slight bow  56  now exists in the side rails  27  of frame  12 . Of course, being under substantial tension, the cables themselves remain straight, lying beneath the upper edge  28  of form  33 . 
       FIG. 18  shows a new roadway segment  39  in the process of being poured, with one end of frame  12  adjacent an existing roadway segment  55 . This circumstance will be encountered where an entirely new roadway is being constructed, and segments are being consecutively poured in end-to-end relation. Concrete  57 , supplied through the chute of a cement truck (not shown), is delivered into the form  33  until it fills the form to reach upper edge  38 . At that time, all of the cables  41  will be completely covered and immersed in concrete. 
     After the concrete has cured, the apparatus  11  can be removed from the pour site. To release the frame  12 , all of the cables  41  are severed between the end of the new roadway segment  39  and respective cable restraint extensions  19 . This is usually done by means of a cutting torch. With the frame  12  free from the cables, the frame can now be lifted first vertically and then horizontally, away from the pour site. Remaining is the form  33 . The elongated sides  34  are next removed, exposing the sides of the roadway segment  39 . Then, the nuts and bolts holding the first and second bulkheads  36  and  37  are removed, allowing the split bulkheads to be removed from the pour site. 
     As shown in  FIG. 28 , a void  59  now exists between existing roadway segment  55  and new roadway segment  39 . This void essentially represents the space taken up by the bulkhead and the outrigger assembly during the pour. By undertaking a second pour, and filling void  59 , an expansion joint  61  is thereby created. It should also be noted that cables extending from adjacent ends of segments  39  and  55  may be joined before the second pour, through the use of splice chucks (not shown). In that way, the roadway segments may further be secured together to resist buckling and heaving. 
     An alternative method of pouring is shown in  FIG. 27 , where two of the frames  12  are set up and arranged in end-to-end relation, to create two new roadway segments  39  at essentially the same time. Although the pouring process is identical to that just described, as illustrated in  FIG. 28 , the roadway segments are separated by avoid  62  which is wider than the void  59  resulting from employing the first method. This wider void is created by the space taken up by the two bulkheads and the two outrigger assemblies associated with adjacent ends of the frames  12 . When a second pour is made to fill void  62 , it necessarily forms a wider expansion joint  63 , shown in  FIGS. 28 and 30 . 
     When multiple lanes of a roadway are manufactured using the apparatus  11 , such as the three lane construction shown in  FIG. 28 , it is evident that when undertaking side-by-side pours of roadway segments  39 , one side  34  of the form  33  is not used. The adjacent side of an existing roadway segment  55  effectively provides the other side of the form. The bulkheads are arranged in contingent relation with this side of the roadway segment  55 , and act in conjunction with one side  34  to confine the pour. 
     Another scenario where the apparatus  11  may be used advantageously, is to repair an old roadway  64  which has become cracked, vertically displaced, or otherwise damaged. First, the damaged section of the old roadway is defined, by cutting around the damaged section using conventional concrete saws. The concrete within the damaged section is subsequently removed and the floor of the excavation is graded. The apparatus  11  is then moved into place, in spaced relation above the excavation, using jacks  52  resting on the adjacent old roadway  64 . Since the existing sidewalls of the old roadway  64  effectively provide the sides of the form  33 , only the bulkheads  36  and  37  need to be installed to confine the pour, as shown in  FIG. 21 . In addition, such damaged sections are not usually the full 60′ length of the frame  12 , but rather assume different special lengths depending upon the extent of the roadway damage. 
     To accommodate the need to manufacture a shorter roadway segment length, frame  12  may be fitted with a secondary outrigger frame  66 , shown in detail in  FIG. 7 . Frame  66  includes a pair of tubular sleeves  67 , each mounted in slidable relation over a respective side rail  27 . Sleeves  67  are interconnected by a cross-member  68  forming a rigid “H” shaped frame. Cross-member  68  is also provided with a pair of angle irons  26  mounted so that a portion of the irons are maintained in spaced relation above the cross-member&#39;s upper surface. 
     Secondary outrigger frame  66  also includes a plurality of outrigger assemblies  68  identical to assemblies  16  and  17 , described above. Each of these assemblies includes a receiver  18  and a cable restraint extension  19 . Each receiver  18  further includes a slot portion  21  to receive a tongue portion  22  of an extension  19 , and the two structures are secured together by means of removable pins  23 . A chuck recess  20  is also provided in the lower end of extension  19 , to receive the nose portion of a chuck  54 . 
     Because there may be a need to locate one or more of the pre-stress cables  41  immediately beneath sleeves  67 , a plurality of receiver plates  69  are attached to the underside of sleeves  67 . These receiver plates include a slot  71  which is sized and configured to receive tongue portion  22  of an extension  19 . It should be noted that there are opposing pairs of receiver plates in longitudinal alignment to accommodate an extension  19 . The right hand pairs of receiver plates  69  will be used when the cables are strung from the first outrigger assembly  16  to the secondary outrigger frame. (See,  FIGS. 23 and 24 ). And, the left hand pairs of receiver plates  69  will be used when the cables are strung from the second outrigger assembly  17  to the secondary outrigger frame  66 . 
       FIG. 21  shows the frame  12  with the secondary outrigger frame  66  properly positioned along side rails  27  for pouring a roadway segment which is relatively short. Means such as compressive or wedging fixtures (not shown) are provided for selectively locking the frame  66  in position along rails  27 . As indicated, only first and second bulkheads  36  and  37  are required in this application, as the sidewalls  72  of the existing roadway segments  55  provide the side portions of the form required for the pour. For this application, where end space is limited, it may be desirable to run and pre-stress cables  41  before frame  12  is lowered into place within the excavation. Alternatively, frame  12  is lowered into the excavation in the same manner previously described, before the cables  41  are strung and pre-stressed. (See,  FIGS. 23 and 24 ). 
     After the concrete has been poured and has had a sufficient amount of time to cure, the frame  12  and the bulkheads  36  and  37  are removed from the excavation, leaving the new roadway segment  39 , shown in  FIG. 22 . Because a void  73  is left at each end of segment  39  from the removal of the outrigger assemblies and the bulkheads, a second pour into each void creates expansion joints  74  to complete the repaired roadway segment  39 . (See,  FIGS. 25 and 26 ). 
     For the purpose of manufacturing beams, posts, and the like, a frame  76 , having a more compact configuration, may be utilized. Frame  76  comprises an elongated “I”-Beam member  32 , a coupler sleeve  77 , and transverse end rails  28  and  29 . Although only one end of frame  76  is shown in  FIGS. 31 and 32 , it will be understood that the opposite end of frame  76  is identical in structural features to that which is shown. End rails  28  and  29  are fitted with outrigger assemblies  78 , identical in features but fewer in number than the outrigger assemblies  16  an  17  described previously. 
     The apparatus  11  employing frame  76 , also includes a form  79 , having elongated sides  81  and split bulkheads  82 , identical in all respects except size, with those corresponding components previously described. In this application, the frame  76  is lowered over the form  79 , and supported by jacks  52 . Cables  41  are strung between the outrigger assemblies, and the height of the frame is adjusted so that the cables lie below an upper edge  83  of the form  79 . The cables are then pre-stressed using a conventional pre-stressing fixture, and locked in place with a chuck  54  nested within a respective cable restraint extension  19 . 
     With the apparatus  11  fully prepared, concrete is then poured into form  79  until its upper surface reaches upper edge  83 . After the concrete is cured, the cables  41  are cut and frame  76  is removed from the pour site. After the bulkheads  82  and the sides  81  are removed, an elongated pre-stressed post  84  remains, as shown in  FIG. 33 . 
     It is also apparent that in a particular application, it may be desirable to have additional sets of cables  41 , interspersed throughout a concrete structure such as a post, pole, or beam. In other words, in addition to having one set of cables  41  arranged in a horizontal plane as shown in  FIG. 33 , for additional strength, additional pre-stressed cables could be included in the concrete structure at different heights and patterns. This could be accomplished by having a three or four part split bulkhead, having cable passages at different elevations and locations. This would also require that the receivers and the cable restraint extensions be of different overall lengths, to secure the pre-stressed cables at alternative heights and locations throughout the poured concrete structure.