Abstract:
A post-tensioned continuous strand hoop reinforcement for concrete foundations is provided. The post-tensioned continuous strand hoop reinforcement compresses the concrete to prevent cracking and significantly reduces foundation deflection and distortion which increases rotational stiffness in anchor caps, spread foundations, and like foundation configurations.

Description:
[0001]    This application is a continuation application of co-pending U.S. Ser. No. 14/187,501 filed Feb. 24, 2014, which claimed priority from U.S. provisional application, Ser. No. 61/793,187 filed Mar. 15, 2013, the priority of which is hereby claimed. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    This invention relates in general to improvements and replacements of steel reinforcing in large concrete support foundations, precast or constructed in-situ, particularly useful for supporting tall, heavy structures including towers which may be used to support wind turbines, power transmission lines, street lighting and signals, bridge supports, commercial signs, freeway signs, ski lifts, and the like. 
         [0004]    More specifically, the continuous strand hoop reinforcement of the present invention may be high strength steel strand or cable sleeved to allow post tension useful in compressing the concrete to exceed loads and splitting stresses in the concrete between other reinforcements with minimal deflection and distortion while reducing the steel weight, volume and length currently required of conventional rebar hoops by as much as one-half. 
         [0005]    2. Description of Related Art 
         [0006]    My earlier U.S. Pat. No. 5,586,417 (my &#39;417 patent) for tensionless pier foundation, U.S. Pat. No. 5,826,387 for pier foundation under high unit compression, U.S. Pat. No. 6,672,823 for perimeter weighted foundation, U.S. Pat. No. 7,533,505 for pile anchor foundation, U.S. Pat. No. 7,618,217 for post tension pile foundation, and U.S. Pat. No. 7,707,797 (my &#39;797 patent) for pile anchor foundation disclose post-tensioned concrete foundations for large supporting structures for which the present invention is applicable. Accordingly, the disclosures of my six aforesaid U.S. patents are expressly incorporated herein by reference as if fully set forth in their entirety. 
         [0007]    Conventionally, rebar hoops are circular (lateral) and positioned around and in contact with the vertical or horizontal reinforcing rebars or bolts of the concrete foundation. The rebar hoops are either circular or otherwise configured lengths of rebar lapped at ends sufficiently to provide bonding to the concrete and reinforcement equal to the strength of the steel rebar. The laps considerably increase the quantity of steel where larger diameter hoops are utilized, since additional rebar is required as the rebar steel strength is typically one-third the steel strength of the strand material. 
         [0008]    Further, conventional hoops are utilized to prevent the separation of the foundation from occurring between the vertical or horizontal (lateral) steel reinforcing rebar or bolts. However, there is a need to provide hoop strands which can be post-tensioned in order to compress the concrete between the vertical or horizontal (lateral) steel reinforcing rebar or bolts and prevent cracking as well as reducing deflection, distortion, cycling, fatigue and increasing structure life. 
       SUMMARY OF THE INVENTION 
       [0009]    The continuous strand hoop reinforcement or continuous strand reinforcing hoops (used synonymously) according to the present invention resists foundation separation between vertical or horizontal (lateral) rebar or bolt steel reinforcing of the concrete support foundation or similar support foundations constructed of other cementious-type materials (herein collectively broadly referred to as “concrete support foundations” or more simply “concrete foundation” or “concrete foundations”). 
         [0010]    The continuous strand hoop reinforcement of the present invention preferably comprises strands made from high strength wires, on the order of 250 ksi, twisted into a flexible cable or the like, having a diameter in cross-section of more or less one-half inch. The strands are greased and rubber-sleeved so as to prevent the high strength strands from adhering or bonding to the concrete foundation upon curing and allow the strands to be post-tensioned, as described hereinafter. Other mechanisms may be used to prevent the flexible high strength strands or cables from engaging with the concrete, such as flexible plastic tubing, to shield the cable from the concrete. Other mechanisms will also be understood by those skilled in the art to permit post-tensioning of the strands or cables within the concrete foundation. 
         [0011]    The covered or coated strands or cables can be placed on large rolls or hooped for simple delivery to project sites. These coated strands or cables may be in lengths of 1000 feet, more or less, allowing a continuous length of steel strand which may be configured and placed in the concrete foundation in a generally circular or spiral configuration in which each expanding hoop is separated by six inches, more or less. The continuous strand hoop reinforcement is thus mostly circumferentially spaced around and in contact with the vertical or horizontal (lateral) rebar and is preferably positioned by guides and wire tied to the other concrete foundation steel reinforcement. 
         [0012]    One end of the continuous coated strands or cables is embedded in the concrete foundation (the “embedded end”) with the strands circumferentially wound around and in contact with the other steel reinforcement of the concrete foundation. The other end of the coated strands or cables exits through or adjacent the top of the concrete foundation at a location to readily permit post-tensioning of the coated strands or cables (the “exposed end”). The embedded end of the coated strands or cables is terminated with an end nut or similar apparatus which secures the embedded end in the concrete foundation and prevents its movement when the coated strand or cable is post-tensioned. The exposed end can also be fitted with an end nut-like apparatus with internal wedges which compress into the metal strand or cable to secure the steel from sliding in the wedge. The steel strand or cable can then be post-tensioned by elongating the strands through the wedges by pulling/jacking or the like against a plate set on or in the concrete to create the post-tensioned strand hoop. 
         [0013]    As previously described, once the foundation concrete obtains sufficient strength to compress the concrete against and between the vertical or horizontal (lateral) rebar or bolt steel, the continuous strand hoop reinforcement can be post-tensioned to prevent or reduce cracking of the concrete by splitting loads. The space between the circumferential continuous strand hoops is determined by the compressive strength required to prevent cracking of the concrete. 
         [0014]    The continuous strand hoop reinforcement contacts and/or ties to all the normal vertical and horizontal (lateral) steel reinforcing when the foundations are flat caps or spreading discs configuration or like. These reinforcing steels are placed near the top and near the bottom. 
         [0015]    In accordance with the foregoing, it is an object of the present invention to replace conventional rebar foundation hoops with a continuous strand hoop reinforcement or continuous strand reinforcing hoops, preferably post-tensioned, for concrete foundation piers, caps, spreading discs and the like which can be pre-cast or constructed in-situ for supporting dynamic tall, heavy, and/or large structures including towers and/or poles. 
         [0016]    A further object of the present invention is to replace conventional rebar hoops for preventing foundation splitting between standard vertical and horizontal (lateral) reinforcing with continuous strand reinforcing hoops, preferably post tensioned, as described herein. 
         [0017]    Another object of the present invention is to provide cost advantage to providing splitting resistance between the vertical and horizontal (lateral) reinforcing steel (rebar and/or bolts) by requiring as much as one-half less of the hoop steel by reinforcing the rebar hoops with continuous strand hoops, preferably post-tensioned. 
         [0018]    Yet a further objective of the present invention is reduce the hoop placement time and effort required by reducing the number of wire tie, steel handling, and manpower required for conventional rebar hoops. 
         [0019]    Still another objective of the present invention is to post-tension the continuous strand hoops in order to compress the concrete significantly reducing foundation deflecting and distortion while increasing rotational stiffness in flat caps, spreading discs or like foundation configurations. 
         [0020]    Further objectives of the present invention are to reduce cycling, fatigue, and greatly increase the foundation life up to as much as four times. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Other objectives, features, and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings while intending to illustrate the invention, the drawings are not necessarily to scale. 
           [0022]      FIG. 1  is a profile view of a tensionless pier foundation as disclosed in my &#39;417 patent, with tower anchor bolts, outer and inner corrugated metal pipes, embedment ring, concrete plug, soil backfill, slurry backfill, and floor, and a continuous strand hoop reinforcement in accordance with the present invention added in place of conventional rebar hoops. 
           [0023]      FIG. 1A  is a profile detailed view showing the exposed ends of the continuous strand hoop reinforcements shown in  FIG. 1 . 
           [0024]      FIG. 1B  is a profile detailed view showing the embedded ends of the continuous strand hoop reinforcements shown in  FIG. 1 . 
           [0025]      FIG. 2  is a profile view of a post-tensioned pile anchor foundation as disclosed in my &#39;797 patent, with tower anchor bolts, perimeter corrugated metal pipe, embedment ring, horizontal (lateral) reinforcing steel, leveling course, pile anchor, and grout trough, and continuous strand reinforcing hoops in accordance with the present invention added in place of conventional rebar hoops. 
           [0026]      FIG. 3  is a top view of the post-tensioned pile anchor foundation shown in  FIG. 2  with tower anchor bolts, perimeter corrugated metal pipe, embedment ring, top and bottom horizontal (lateral) reinforcing steel, leveling course, pile anchors, and grout trough, and the continuous strand reinforcing hoops with coiled strand hoop guides in accordance with the present invention. 
           [0027]      FIG. 4  is a profile view of the P&amp;H spread foundation, with tower anchor bolts, pedestal inner corrugated metal pipe, pedestal outer corrugated metal pipe, base perimeter corrugated metal pipe, embedment ring, grout trough, top horizontal (lateral) steel bolts, bottom horizontal (lateral) steel bolts, and leveling course, and continuous strand reinforcing hoops with the coiled strand hoop guides in accordance with the present invention. 
           [0028]      FIG. 5  is a top profile view of the P&amp;H spread foundation shown in  FIG. 4 , with post-tensioned anchor bolts, pedestal inner corrugated metal pipe, pedestal outer corrugated metal pipe, base perimeter metal pipe, grout trough, and top horizontal (lateral) steel bolts, with the coiled strand hoop guides, and continuous strand reinforcing hoops. 
           [0029]      FIG. 6  is an enlarged profile view of a single coiled strand hoop guide with notches for strand placement in accordance with the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Although preferred embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its scope to the details of construction and arrangement of this specific embodiment. The invention is capable of being practiced or carried out in various ways. Also, in describing the preferred embodiment, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term; includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
         [0031]    Referring to the drawings,  FIGS. 1-5  illustrate typical large concrete support foundations for tall and heavy structures including towers which may be used to support wind turbines, power transmission lines, street lighting and signals, bridge support, commercial signs, freeway signs, ski lifts and the like. 
         [0032]    The tensionless pier foundation shown in  FIG. 1  is designated by reference numeral  10 . Foundation  10  includes circumferentially spaced rings, tower anchor bolts, including outer anchor bolts  11  and inner anchor bolts  101 . The anchor bolts  11  and  101  extend from an embedment ring  18  near the bottom of the foundation up through the grout trough  20  and above the foundation  10 . The tower anchor bolts  11  and  101  may number 100 or more and are radially paired in a cylindrical configuration which may have an average diameter of 14 ft. The tower anchor bolts  11  and  101  are typically steel rods about one and one-half inch in diameter. The tower anchor bolts  11  and  101  are generally centered horizontally (laterally) within a concrete filled annulus  103  bounded by an inner corrugated metal pipe  13  and an outer corrugated metal pipe  12  extending the length (depth) of the foundation which may be 30 ft. or more. Inside the inner corrugated metal pipe  13 , a concrete plug  14  is situated at and above the bottom covered with loose soil backfill  17  extending to the bottom of the foundation floor  15  at the top of the foundation. 
         [0033]    The continuous strand hoop reinforcement in accordance with the present invention shown in  FIG. 1  is generally designated by reference numeral  16  and includes an inner hoop reinforcement  105  and an outer hoop reinforcement  107 . Both the inner hoop reinforcement  105  and the outer hoop reinforcement  107  are embedded adjacent the bottom of the concrete foundation at the detail bottom end identified by reference numeral  109  and shown in  FIG. 1B . The inner hoop reinforcement  105  is spirally wound upwardly around the ring of inner anchor bolts  101  where the hoop exits the concrete foundation at detail top end identified by reference numeral  111 , shown in  FIG. 1A . While the continuous strand reinforcing hoops  105  and  107  are shown in  FIG. 1  as wound in the same direction and generally adjacent each other, those skilled in the art will readily understand that the hoops can be wound in the same direction in a spaced relationship and even wound in opposite directions as appropriate. 
         [0034]    The continuous strand reinforcing hoops  105  and  107  comprise strands preferably made of high strength wires, approximately 250 ksi, twisted into a cable or the like, more or less one-half inch in diameter, which is greased and rubber-sleeved, to prevent the reinforcement hoops  105  and  107  from bonding with the concrete foundation. Alternate structures and methods can be used to cover or coat the stretchable wire or cable in order to prevent the bonding, as will be understood by those skilled in the art. Terminating the continuous strand reinforcing hoops  105  and  107  is a wedged nut-like apparatus  113  placed at each end of the continuous strand hoops. At the embedded end shown at reference numeral  109 , the wedged nut-like apparatus bonds to the concrete and prevents the embedded end of the continuous strand hoops  105  and  107  from moving during any post-tensioning operation. Post-tensioning of the continuous strand hoops  105  and  107  is accomplished by pulling the exposed end at reference numeral  111 , shown in  FIG. 1A , through the wedged nut-like apparatus  113  against a base plate (not shown) positioned against the outside of outer corrugated pipe  12 , as is well understood by those skilled in the art. 
         [0035]    The pile anchor foundation shown in  FIGS. 2 and 3  is designated by reference numeral  30 . Foundation  30  includes tower anchor bolts  31  extending from the embedment ring  33  near the bottom of the concrete foundation cap  40  through the grout trough  35  and above the top of the foundation cap  40 . The tower anchor bolts  31  may number 100 or more and are radially paired in cylindrical configuration which may have an average diameter of 24 ft. centered in the concrete foundation and 5 ft. in depth bounded by a perimeter corrugated metal pipe  32  constructed in-situ atop a concrete or gravel leveling course  36 . The tower anchor bolts  31  are typically steel rods having a one and one-half inch diameter. The concrete foundation cap  40  may have horizontal (lateral) steel near the top and bottom of the concrete foundation cap  40  with numeral reference designation  37  for the upper horizontal (lateral) steel and numeral reference designation  38  for the lower horizontal (lateral) steel. The horizontal (lateral) steel (both top  37  and bottom  38 ) is circumferentially placed and connected by the continuous strand reinforcing hoops  39  and  139  which connect to the top horizontal steel  37  and bottom horizontal steel  38 , respectively. The continuous strand hoop reinforcements  39  and  139  are preferably positioned by coiled strand hoop guides  41  and  141 , top and bottom respectively. While ten coiled strand hoop guides  41  are shown circumferentially spaced around in  FIG. 3 , the number of such guides can vary depending upon the size of the foundation  30  and should preferably range between about 6 and about 12. 
         [0036]    As shown, the continuous strand reinforcing hoops  39  and  139  are spirally wound in a generally horizontal configuration, extending adjacent the center for the embedded end  115  and adjacent the foundation exterior for the post-tensioning end  117  (see  FIG. 3 ). The windings are preferably spaced apart approximately six inches, thus the notches  121  of the guide  41 / 63 , shown in  FIG. 6 , are similarly spaced. The structure and operation of the continuous strand reinforcing hoops  39  and  139  are the same as previously described for strand hoops  105  and  107  in the  FIG. 1  embodiment. 
         [0037]    The P&amp;H spread foundation shown in  FIGS. 4 and 5  is designated by reference numeral  50 . Foundation  50  includes tower anchor bolts  51  extending from the embedment ring  55  near the bottom of the foundation through the grout trough  56  and above foundation  50 . The tower anchor bolts  51  may number 100 or more, with a 1½″ diameter, and are radially paired in a cylindrical configuration which may have an average diameter of 14 ft. The tower anchor bolts  51  are centered within a concrete filled annulus foundation pedestal  62  bounded by the pedestal outer corrugated metal pipe  53  extending the length (depth) of the foundation pedestal  62  which may be 10 ft. and is filled with concrete. The foundation pedestal  62  may also include an inner corrugated metal pipe  52 . 
         [0038]    The foundation pedestal  62  may be embedded 5 ft. into the foundation base spread element  6  l which may be 60 ft. in diameter and bounded by the base perimeter corrugated metal pipe  54 . The P&amp;H spread foundation  50  may have horizontal (lateral) steel near the top and bottom of the spread foundation  50  with numeral reference designation  57  for the bottom horizontal (lateral) steel and  58  for the top horizontal (lateral) steel. The horizontal (lateral) steel (both top  58  and bottom  57 ) is circumferentially placed and connected by the continuous strand reinforcing hoops  60  positioned by the coiled strand hoop guides  63 . 
         [0039]    The continuous strand reinforcing hoops  60  have the same structure and operation as previously described in connection with the continuous strand hoop reinforcements  105  and  107  of  FIG. 1  and the continuous strand reinforcing hoops  39  and  139  of  FIGS. 2 and 3 . The continuous strand reinforcing hoops  60  extend from the embedded end  125  to the exposed end  127 . The coiled strand hoop guide  63  is also illustrated in  FIG. 6  and has the same structure and operation as previously described for coiled strand hoop guide  41  of the embodiment shown in  FIGS. 2 and 3 . 
       Construction Sequence and Special Features 
       [0040]    The tensionless pier foundation  10  may be constructed in-situ by excavating a nearly circular hole by drill rig or track excavator to the intended tensionless pier foundation depth. The outer corrugated metal pipe  12  is centered in the excavation plumb and the annular space between the edge of excavation and the perimeter of the outer corrugated metal pipe  12  is backfilled with slurry  19 . The inside tower anchor bolts  101  are loaded into the bolt holes in a template (not shown) suspended above the outer corrugated metal pipe  12 . The template and inner bolts  101  are lifted from inside the outer corrugated metal pipe  12  and suspended along side the excavation for placement of the embedment ring  18  on the inner tower anchor bolts  101 . Following loading of inner tower anchor bolts  101  in the embedment ring  18 , the inner tower anchor bolts  101  are lowered inside the outer corrugated metal pipe  12  while the continuous strand hoop reinforcement  105  is wound and wire tied around the inner tower anchor bolts  101  in a generally spherical or helical configuration. Once the continuous strand hoop reinforcement  105  is wound around the inner tower anchor bolts  101  the template and inner tower anchor bolts  11  are again lifted from inside the outer corrugated metal pipe  12  and the same procedure followed for placement of the continuous strand hoop  107  around outer tower anchor bolts  11 . After lowering and plumbing the tower anchor bolts  11  and  101 , the inner corrugated metal pipe  13  is placed and plumbed, the concrete plug  14  poured and set, the soil backfill  17  placed, and the tensionless pier foundation  10  concrete monolithically poured. Once the concrete has sufficiently cured and set, the anchor bolts  11  and  101  and the continuous strand hoop reinforcements  105  and  107  can be appropriately post-tensioned. 
         [0041]    The pile anchor foundation  30  may be constructed in-situ by excavating for the concrete foundation cap  40 , installing the pile anchors  131 , pouring the leveling course  36 , installing the tower anchor bolts  31  with the embedment ring  33  near the bottom of the foundation cap  40  and the template ring (not shown) at the top centered in the foundation cap  40 . The bottom horizontal (lateral) reinforcing steel  38  and the coiled strand hoop guides  141  are installed at approximately equal intervals between selected bottom horizontal steel  38  and wire tying continuous strand reinforcing hoops  139  in the coiled strand hoop guides  141 . The top horizontal (lateral) reinforcing steel  37  is placed and coiled strand hoop reinforcing guides  41  installed between selected top horizontal (lateral) reinforcing steel  37 . Continuous strand hoop reinforcing  39  is then placed and tied into the coiled strand hoop guides  41 . Finally, the perimeter corrugated metal pipe  32  is placed and the concrete foundation cap is monolithically poured. Once the concrete has sufficiently cured and set, the pile anchors  131  and continuous strand reinforcing hoops  39  and  139  can be appropriately post-tensioned in order to complete the pile anchor foundation. 
         [0042]    The P&amp;H spread foundation  50  may be constructed in-situ by excavating for the foundation base spread element  61 , pouring the leveling course  59 , installing the tower anchor bolts  51  centered in the foundation  50  footprint with the embedment ring  55  near the bottom of the foundation  50  and template ring (not shown) at the top centered in the annular space between the pedestal outer corrugated metal pipe  53  and the pedestal inner corrugated metal pipe  52 . After forming the pedestal foundation  62 , the elements of foundation base spread  61  are installed beginning with the base perimeter corrugated metal pipe  54 , then inserting the bottom horizontal (lateral) steel bolts through holes in radial alignment in each of the three corrugated metal pipes, then placing  6  coiled strand hoop guides  63  at approximately 60° intervals between selected bottom horizontal (lateral) steel bolts  57 , then placing and wire tying continuous strand hoop reinforcement  60  into the coiled strand hoop guide  63 , then install the top horizontal (lateral) steel bolts,  6  coiled strand hoop guides  63 , and the continuous strand hoop reinforcing steel  60  same as required for at the bottom of the spread foundation  50 . Following installation of steel elements of the spread foundation  50  the concrete is poured monolithically. After adequate concrete strength is obtained, the horizontal (lateral) steel bolts top  58  and bottom  57  are post-tensioned followed by post-tensioning of the continuous strand hoop reinforcement  60 . 
         [0043]    The foregoing descriptions for the construction sequence of the tensionless pier foundation  10 , the pile anchor foundation  30  and the P&amp;H spread foundation  90  are intended to be exemplary and should not be considered as limiting, since other sequences and possible alternative procedures are readily available and understood by those skilled in the art.