Abstract:
A system of forms for facilitating the pouring of concrete into slabs, including a single &#34;universal&#34; screed stake with four vertically spaced pairs of fingers for selective use with screeds of four different vertical dimensions, each of the pairs of fingers receiving the lower edge of one of the screeds with the top of the stakes being received in a downwardly opening pocket formed by a hem on the upper edge of the screed. A novel stake configuration including the shape and location of the fingers and the curvature of the stake at the upper end thereof is dislcosed as is a novel screed construction including the pocket formed at the upper edge thereof and the skirt at the bottom edge thereof. Together, the screed and stakes cooperate to retain the screed on the stakes.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a system for forming the joints of concrete slabs used in the construction of roadways, floors and the like. The basic system of forms, including screed and screed stakes, is well known and is illustrated, for example, in the Artigalas, et al. U.S. Pat. No. 3,057,269, dated Oct. 9, 1962, the Tone, et al. U.S. Pat. No. 3,357,324, dated Dec. 12, 1967, the Self U.S. Pat. No. 3,561,721, dated Feb. 9, 1981, the Tone U.S. Pat. No. 3,401,612, dated Sept. 17, 1968, the Welsh U.S. Pat. No. 3,497,172, dated Feb. 24, 1970, and the Berry U.S. Pat. No. 4,012,159, dated Mar. 15, 1977. 
     The screed stakes are generally made of metal, approximately 0.06 to 0.08 inches in thickness, approximately 1.00 to 1.25 inches in width and from 12 to 24 inches in length, depending upon the type of earth in which they are to be supported. Such stakes generally have a flat top and a pointed bottom to facilitate driving into the ground, as well as a longitudinal reinforcing bead or channel running from the pointed bottom to a point adjacent to the flat top. The flat top also facilitates insertion into a downwardly opening pocket formed on the top edge of the sheet metal screed with which the stakes are used. Such stakes may also be provided with upwardly opening pocket into which the lower edge of the screed may be inserted. In practice, this pocket often takes the form of one or more &#34;fingers&#34; formed out of the stake metal and extending upwardly alongside the stake. 
     The vertical depth of the concrete slabs being poured, and thus the vertical width of the screed necessary to form the key joint in the slab, differs substantially with the four typical dimensions being 3.5, 4.5, 5.5 and 7.5 inches. With generally known systems, it has been necessary to maintain an inventory of stakes with fingers at different distances from the top end of the stake, so that a screed of the desired vertical dimensions may be secured to the stake. The maintenance of this inventory of stakes is costly, not only in the initial cost of procuring the stakes, but in the manpower necessary to maintain their separation and in the storage space needed in the transportation to and storage thereof at the construction site. The need for a &#34;universal&#34; stake which may be used with screeds with differing vertical dimensions has been long recognized. 
     Known attempts to provide a stake for use with more than one dimension of screed have included the location of a single finger on opposite sides of the central reinforcing bead in the stake at two different vertical heights. Such single finger stakes have the disadvantage in that the holding capabilities of the single finger are limited and in addition may permit an undesirable rotation between the screed and stake. In addition, two different stakes with the four standard concrete slab depths are generally required. 
     It has also been known to utilize the screed receiving fingers in pairs at a given vertical distance from the top edge thereof. However, the use of pairs of fingers at multiple depths has presented two problems, i.e., (1) the stake has been impermissibly weakened by the cutting of the metal to form the multiple fingers and (2) the location of the fingers for dimensions of screed other than the one in actual use has interfered with the securing of the screed to the stake. 
     More recently, applicants have devised a &#34;universal&#34; stake provided with three pairs of fingers, with one of the pairs of fingers serving to receive the bottom edge of two different widths of screed. In this system where two different widths of screed use a common pair of fingers, the top of the stake is received in the downwardly opening pocket of one of the two screeds, and the top of the stake passes through a slot in the screed channel when in use with the other dimension of screed. This system is described and claimed in applicant&#39;s pending application Ser. No. 376,608, filed May 10, 1982, now U.S. Pat. No. 4,428,556, dated Jan. 31, 1984, and assigned to the assignee of the present invention. 
     It is a primary object of the present invention to obviate the deficiencies of known systems and to provide a novel system having a single novel &#34;universal&#34; stake usable with each of four novel screeds of standard widths, as well as a novel method of securing the screed to the stakes. 
     The advantages of the present system will be readily apparent to one skilled in the art from the claims and from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     THE DRAWINGS 
     FIG. 1 is a front elevation view of one embodiment of the novel stake of the present invention; 
     FIG. 2 is a side elevation view of the stake of FIG. 1; 
     FIG. 3 is an enlarged side elevation view of the fingers of the stake of FIGS. 1 and 2; 
     FIG. 4 is a side elevation view of a second embodiment of the fingers of the stake of FIGS. 1 and 2; 
     FIG. 5 is a pictorial representation of the relative dimensions of one embodiment of four sizes of screed which may be used in the system of the present invention; 
     FIG. 6 is a side elevation view of the top portion of the stake of FIGS. 1 and 2 in proximity to the upper edge of the screed illustrated in FIG. 5; 
     FIG. 7 is a side elevation view of an intermediate portion of the stake of FIGS. 1 and 2 in proximity to the lower edge of the screed illustrated in FIG. 5; 
     FIGS. 8, 9, and 10 are side elevation views of portions of the stake of FIGS. 1 and 2 and the screed of FIG. 5 illustrating a method of securing the screed to a line of stakes; and 
     FIG. 11 is a schematic illustration of the frictional binding action of the screed to the stake at the upper edge of the screed; 
     FIG. 12 is a schematic illustration of the frictional binding action of one embodiment of screed to the stake at the lower edge of the screed; and 
     FIG. 13 is a schematic illustration of the frictional binding action of a second embodiment of the screed to the stake at the lower edge of the screed. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIGS. 1 and 2 where a preferred embodiment of the stake of the present invention is illustrated, the stake 10 may be made of flat steel of approximately 0.07 inches in thickness and may be formed with a central reinforcing bead 12 approximately 0.5 inches wide and 0.25 inches deep. The finished width of the stake is approximately 1.25 inches, but may be slightly larger at the upper end 14 thereof in the area where the reinforcing bead 12 does not extend. The length of the stake may be varied as a function of the anticipated soil conditions into which the stake is to be driven, i.e., typical lengths are 12 inches, 15 inches, 18 inches and 24 inches. 
     With continued reference to FIGS. 1 and 2 where like numerical indications have been applied to like elements, the stake 10 is provided with four vertically spaced pairs of &#34;fingers&#34;, with one pair of fingers 16, 18, 20, and 22 located respectively to form a pocket approximately 7.5, 5.5, 4.5 and 3.5 inches from the top of the stake. 
     As shown in FIGS. 1 and 2, each of the fingers 16, 18, 20, 22 may be the same length L with a distance D between like points on vertically adjacent fingers being the same for the uppermost three pairs of fingers 18, 20, 22, i.e., about one inch. The distance between the two lowermost pairs of fingers 16, 18 is approximately twice that between the other pairs of fingers 18, 20, 22. 
     Note that the upper three pairs of fingers are found on the stake 10 within a space equal to (2 D+L), or slightly less than 2.5 D. Note also that all four pairs of fingers are found on the stake 10 within a space equal to (4 D+L), or slightly less than 4.5 D. The location of all four pairs of fingers within this distance is possible without impermissibly weakening the stake because the length L of each finger is significantly reduced, a reduction which is in turn possible because of the unique configuration and interaction of the screed and stake as is subsequently discussed in greater detail. 
     As shown in greater detail in FIG. 3, each of the fingers 16, 18, 20, and 22 of FIGS. 1 and 2 may be formed into a generally arcuate shape having a radius R of about 0.25 inches. An alternative configuration of the fingers of the stake of FIGS. 1 and 2 is illustrated in FIG. 4 where the finger is formed of a generally upwardly and outwardly portion 36 integral with the stake and an upwardly and inwardly portion 38. In both cases, the free end of the finger is spaced a distance S from the stake less than the thickness T of the stake and is upwardly and inwardly inclined with respect to the stake for reasons subsequently explained in greater detail. 
     With reference again to FIG. 2, it is apparent that the portion of the stake 10 above the uppermost pair of fingers 22 is generally curved toward the finger side of the stake with the flat top 39 thereof disposed desirably in the approximate plane of the stake. The radius of curvature of this bend may be, e.g., approximately 3.5 to 4.5 inches. 
     The four standard sizes of screed are illustrated in FIG. 5. As shown in FIG. 5, the stake of FIGS. 1 and 2 may be used with a screed 24 of 3.5 inches in depth by inserting the lower edge 26 thereinto the pocket formed by the fingers 22 and by receiving the top 39 of the stake in the pocket 28 formed at the upper edge thereof. Likewise, the stake of FIGS. 1 and 2 may be used with a screed 30, 32, or 34 with the lower edge 26 thereof respectively received within the pairs of fingers 20, 18, and 16, and with the top 39 of the stake received within the pocket 28 formed at the upper edge 28 thereof. 
     With continued reference to FIG. 5, it may be seen that the lower portions of the three narrowest screed, including the skirt, are desirably the same, e.g., about 0.78 inches, while the upper portion desirably increases proportionally to the width or vertical height of the screed, e.g., about one-third of the total increase. The other two-thirds of the total increase for all but the 7.5 inch screed is absorbed in the central channel portion. However, the more substantial total increase between the 5.5 and 7.5 inch screed is uniformly spread among the three portions. 
     As shown in greater detail in FIG. 6, the pocket 28 is formed by a downwardly extending hem having a first portion 50 immediately alongside the screed, a second portion 52 extending away from the screed, and a third and terminal portion 46 extending downwardly and away from the screed. Note that the distance O between the point 40 of greatest lateral projection toward the screed and the edge 42 of the flat top of this stake on the side thereof facing away from the screed is less than the spacing P between the free end 44 of the pocket 28 formed at the upper edge of the screed. This distance O, however, is greater than the distance Q where the inclined portion 46 of the pocket begins. This ensures that the edge 42 on the top 39 of the stake 10 will pressurally engage the inner surface of the inclined portion 46 of the hem as the pocket 28 of the screed is forced downwardly over the top of the stake with the upper flat portion 48 of the screed in contact with the projection 40 of the stake. 
     The inclined portion 46 of the pocket of the screed is desirably resilient, as subsequently explained, but has sufficient rigidity to ensure that the top of the screed cannot be inserted between screed and the portion 50. This spring-like effect is enhanced by the configuration of the hem in the first portion 50, and outwardly extending second portion 52. 
     With reference to FIG. 7, the lower edge 26 of the screed includes a flat surface 52 generally coplanar with the surface 48 of the upper portion thereof. This lower edge of the screed 26 may be formed into a surface inclined towards the plane of the surfaces 52 and 48. 
     With continued reference to FIG. 7, the lower edge 26 of the screed will be received within the pocket formed by the finger 54. As may be seen from FIG. 7, the distance X is desirably slightly less than the distance (D-L) with the spacing Y greater than the opening Z between the free end of the finger 54 and the surface 56 of the stake out of which the finger 54 is formed. 
     The operation of the system may be more readily understood by reference to FIGS. 8, 9 and 10. As illustrated in FIG. 8, a line of stakes 16 may be driven into the ground to the desired depth and the appropriate screed 62 for that depth brought into proximity to the line of stakes. As illustrated in FIG. 8, the plane 64 of the screed, i.e., the plane passing through the generally coplanar flat surfaces 66 and 68, is inclined to the plane of the plane 70 of the stake, by an angle of about thirty degrees. 
     As shown in FIG. 8, the inclined skirt 76 on the lower edge of the screed 62 is at an angle A to the plane of the screed. As shown in FIG. 8, this skirt 76 may be inserted between the free end 78 of the fingers 72 and the surface 70 of the stake. There is desirably a camming action which results from the engagement of the elbow 80 on the outer surface 82 of the fingers which facilitates the positioning of the screed 62 relative to the stake 60, as illustrated in the lower portion of FIG. 9. 
     As the lower edge of the screed is downwardly inserted within the pocket formed by the stake 72, the top portion 84 of the screed moves from the position illustrated in dotted lines in FIG. 9 to the position shown in solid lines. Once in the position illustrated in FIG. 9, the screed 62 may be pressed downwardly over the stake to simultaneously move the inclined surface 76 of the skirt of the screed into contact with the free end 78 of the finger 72 and the inner inclined surface 86 into contact with the flat top 88 of the stake. 
     As illustrated in FIG. 10, a secure attachment of the screed 62 to the stake 60 is ensured by the engagement of the curved surfaces 74 and 68 (seen in FIGS. 8 and 9), and by the engagement of the top 88 of the stake with the inclined surface 86. As shown schematically in FIG. 11, the horizontal forces exerted by the stake 60 on the screed 62 provide a force couple tending to flex the inclined portion 46 of the screed hem away from the plane of the screed. It should be understood that measurable movement is not required to stress the screed and stake sufficiently to establish the desired friction bind. 
     At the same time, and with continued reference to FIG. 10, the downward movement of the screed 62 relative to the stake 60 inserts the lower edge of the screed 62 into the pocket formed by the finger 72 of the stake sufficiently for pressural engagement between the inclined skirt 76 and the free end 78 of the finger 72. Note in FIG. 10 that the flat surface 66 of the lower portion of the screed 62 engages the flat surface 70 of the stake, (seen in FIG. 8), as may the free end of the inclined skirt 76. 
     As shown schematically in FIG. 12, the stake 60 exerts opposing lateral forces on the screed 62. Where the end of the skirt terminates in the plane of the screed, the stake 60 exerts three horizontal forces as shown in FIG. 13. These forces tend to flex the inclined skirt toward the plane of the screed and ensure a frictional bind between the screed and stake. 
     It should be recognized that the stake is generally much more substantial than the screed, and that deformation of the screed should therefore be expected before any deformation of the stake. 
     In addition to the wedging action and spring bias friction lock of the pocket of the screed over the top of the stake, and in addition to a similar relationship between the skirt at the lower edge of the screed with the ends of the fingers, these opposing lateral forces are supportive and provide a particularly secure frictional bind when acting in concert. 
     As also shown in FIG. 10, a conventional flexible screed cap 90 may be attached over the uppermost or closed portion of the pocket at the top of the screed. This screed cap may be removable or nonremovable as desired. Note that the configuration of the pocket eliminates entry of the flat top 88 of the stake into the uppermost portion of the pocket and thus eliminates distortion of the portion of the pocket over which the screed cap fits. 
     ADVANTAGES AND SCOPE OF THE INVENTION 
     As is readily apparent from the claims and from the foregoing description, the system of the present invention obviates many of the inventory, transportation and storage problems of known systems with a significant reducton in cost. The stake may be utilized with screed of four different vertical dimensions, and may be utilized both intermediate the length of the screed and at the ends thereof where joints are required. 
     The use of the double fingers provides increased gripping and rotational stability to the screed and facilitates joining the screed, i.e., one finger may be used for each of two abutting sections of screed. 
     The use of a spring biased screed structure at the bottom edge of the screed to provide a frictional bind to the stake is effective, and permits a significant reduction in the amount of metal which must be cut from a stake in order to form fingers with adequate resiliancy. The use of a spring biased screed.