Patent Publication Number: US-11661718-B2

Title: Concrete pier foundation with lateral shear reinforcing loops and methods of constructing the same

Description:
This application claims priority from U.S. provisional application Ser. No. 62/703,217, filed Jul. 25, 2018. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to concrete foundations used to support tall, heavy and/or large towers and the like, and to methods for the construction thereof. 
     Description of the Related Art 
     Concrete foundation structures of various kinds have been developed to support commercial signs, traffic signs, light poles and the like. To support larger structures including tall and heavy towers and wind turbines that exert significant overturning force on the foundation. Applicant developed and commercialized a tensionless pier foundation which is described in U.S. Pat. No. 5,586,417 (“the &#39;417 patent”). The &#39;417 patent is hereby expressly incorporated by reference as if fully set forth in its entirety herein. 
     The tensionless pier foundation described in the &#39;417 patent includes a concrete foundation formed as a cylinder having an outer boundary shell defined by a corrugated metal pipe (CMP) and an inner boundary formed by a second CMP of smaller diameter. Elongated high strength steel bolts run from an anchor flange near the bottom of the concrete cylinder vertically up through the concrete to extend above the upper end of the foundation and through a connecting flange for the supported structure to be connected on top of the foundation. The bolts are encased in sleeves or hollow tubes over a substantial portion of their vertical extent in the concrete to allow the encased portion of the bolts to be stretched and thus tensioned. With such tensioning of the bolts, the concrete is kept under constant compression while the bolts are always in static tension. Thus, the pier foundation in the &#39;417 patent is referred to as “tensionless” due to the absence of tensile stress on the concrete. 
     The &#39;417 patent construction was a significant improvement over previously known concrete foundations that incorporated a reinforcing steel bar matrix and were subject to repeatedly alternating tensile and compressive loads on the concrete, leading to fatigue and, in many cases, premature failure. Additional improvements in tensionless concrete foundations are shown in Applicant&#39;s other U.S. Pat. Nos. 8,720,139 (“the &#39;139 patent”) and 9,340,947 (“the &#39;947 patent”), among others. The complete disclosures of the &#39;139 and &#39;947 patents are hereby expressly incorporated by reference as if fully set forth in their entirety herein. 
     In addition to tension and compression loads, concrete foundations are also subject to shear stress. Therefore, it would be beneficial to have a tensionless pier foundation that is more resistant to shear stress and that can be constructed in various configurations to reduce the overall cost of the foundation, particularly when constructing in rock or stable soils. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention is directed to a pier foundation having a plurality of elongated tower anchor bolts embedded within sleeves in a concrete pier and secured at their lower ends to an anchor or embedment ring to form a tower anchor bolt cage. The upper ends of the anchor bolts extend above the top of the concrete so that the bolts, which bear the tensile load, can be post-tensioned to keep the concrete pier under compression in like manner to the construction described in the &#39;417 patent. To increase the lateral shear stress resistance of the foundation, at least a lower portion, and preferably at least the bottom third, of the concrete pier is surrounded by a spiral hoop encasement formed by hoop steel around the perimeter of the tower anchor bolt cage. 
     The present invention is also directed to a pier foundation in which the spiral hoop encasement encircles nearly the entire vertical extent of the pier foundation. When constructed in rock or stable soils that, when drilled or excavated, leave side walls that stand vertically, the full vertical extent spiral hoop encasement eliminates the need for an outer CMP and, depending upon the formation of the center of the pier, can also eliminate the need for an inner CMP as well. 
     Addition, the present invention is directed to various methods of constructing a pier foundation having a spiral hoop encasement at reduced cost, particularly in rock or stable soils. 
     Accordingly, it is an object of the present invention to provide a concrete pier foundation that is highly resistant to both upset and lateral shear stress. 
     Another object of the present invention is to provide a concrete pier foundation in accordance with the preceding object that is maintained under compression in excess of expected tension forces when resisting upset of a supported tower while at least, the bottom portion of the foundation is surrounded by a spiral hoop encasement for increased lateral shear resistance. 
     A further object of the present invention is to provide a concrete pier foundation in accordance with the preceding objects in which the spiral hoop encasement is formed by hoop steel around the perimeter of the tower anchor bolt cage. 
     Yet another object of the present invention is to provide a concrete pier foundation in accordance with the preceding objects in which the spiral hoop encasement extends nearly the full vertical extent of the foundation from the anchor ring at the base to or near the top of the concrete. 
     Still another object of the present invention is to provide a concrete pier foundation in accordance with the preceding object in which the foundation is constructed without an outer CMP. 
     A further object of the present invention is to provide a concrete pier foundation in accordance with the preceding two objects in which the foundation is constructed in rock or stable soil without either an outer CMP or an inner CMP. 
     A still further object of the present invention is to provide a concrete pier foundation in accordance with the preceding object in which the foundation is formed within a dug-out annular trench with native soil remaining undisturbed inside the area surrounded by the trench. 
     Yet a further object of the present invention is to provide a concrete pier foundation in accordance with the object before the preceding object in which the foundation is formed by excavating a cylindrical hole and filling the entire hole, including the center area encircled by the bolt cage, with concrete. 
     Another object of the present invention is to provide one or more methods of installing a concrete pier foundation having a tower anchor bolt cage at least partially wrapped with a spiral hoop encasement for lateral shear reinforcement in which the foundation is constructed without an outer CMP, or without either an outer CMP or an inner CMP. 
     Yet another object of the present invention is to provide a method of constructing a concrete pier foundation without any CMPs in accordance with the preceding object that includes digging an annular trench with native soil remaining undisturbed inside the area surrounded by the trench and filling the trench with concrete after the tower anchor bolt cage wrapped with the spiral hoop encasement is positioned therein. 
     Still another object of the present invention is to provide a method of constructing a concrete pier foundation without any CMPs in accordance with the object before the preceding object that includes digging a cylindrical hole and filling the hole with concrete after the tower anchor bolt cage wrapped with the spiral hoop encasement is positioned therein. 
     A further object of the present invention is to provide a method of constructing a laterally reinforced concrete pier foundation that includes excavating a hole, assembling a tower anchor bolt cage including a plurality of sleeved anchor bolts in an annular arrangement and secured at their lower ends to an anchor ring, wrapping an outer perimeter of the tower anchor bolt cage with a spiral loop steel addition over at least a lower end thereof to provide lateral shear reinforcement to the pier foundation, and securing the wrapped tower anchor bolt cage with concrete after the cage is positioned within the hole with the anchor ring at the bottom of the pier. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a concrete pier foundation like that disclosed in the &#39;417 patent. 
         FIG.  1 A  is a cross-sectional view of the upper end of the pier foundation shown in  FIG.  1   . 
         FIG.  2    is a pier foundation with a lateral shear steel addition or spiral hoop encasement surrounding a lower portion of the pier in accordance with a first embodiment of the present invention. 
         FIG.  3    is a concrete pier foundation constructed without an outer CMP and having a spiral hoop encasement that extends over the vertical extent of the pier in accordance with a second embodiment of the present invention. 
         FIG.  4    is a concrete pier foundation with a spiral hoop encasement and no outer CMP like that shown in  FIG.  3    but constructed in accordance with a third embodiment of the present invention, with the hole being excavated as an annular trench that surrounds a central area of undisturbed native soil, eliminating the need for an inner CMP. 
         FIG.  5    is a concrete pier foundation with a spiral hoop encasement according to a fourth embodiment of the present invention in which, being constructed without CMPs, a cylindrical hole is excavated and then filled with concrete. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood that the embodiments described herein are disclosed by way of illustration only. It is not intended that the invention be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. Also, in describing the preferred embodiments, 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. 
     A concrete pier foundation like that disclosed in the &#39;417 patent is shown in  FIG.  1   . The concrete pier foundation, generally designated by reference numeral  10 , includes an outer corrugated metal pipe (CMP)  12 , an inner CMP  14  and a plurality of tower anchor bolts  20 ,  21  fitted within sleeves  30  and secured at their lower ends to an anchor ring  22  to form a tower anchor bolt cage generally designated by reference numeral  13 . The tower bolt cage  18  is arranged in the annular area  24  formed between the outer and inner CMPs  12 ,  14 , as shown in  FIG.  1 A , with the anchor ring  22  at the bottom of the excavation. The outer diameter of the tower anchor bolt cage  18  is generally on the order of about 14 feet. After the concrete is poured between the CMPs, the upper ends of the tower anchor bolts  20 ,  21  extend upwardly to project above the top of the concrete for post-tensioning thereof. As shown in  FIG.  1   , the lowermost ends of the bolts adjacent and above the anchor ring  22  are not covered by the sleeves  30  to facilitate frictional engagement with the concrete. The sleeves may be hollow tubes or a sleeved effect may be obtained by wrapping the bolts in plastic tape, coating the bolts with a suitable lubrication, or the like. Reference is made to the &#39;417 and &#39;947 patents for a more detailed description of the structure and construction of the basic pier foundation  10  shown in  FIG.  1   . 
     According to a first embodiment shown in  FIG.  2   , the present invention is directed to a pier foundation generally designated by reference numeral  100 . As variously described in the &#39;417 and &#39;947 patents, the outer CMP  12  is initially placed within a hole or excavation formed in the ground and generally designated by reference numeral  16 . The bolt cage  18  is installed vertically inside the outer CMP  12  with the anchor ring  22  at the bottom. The tower anchor bolts are nutted both atop and below the anchor ring to secure the anchor ring in place near the bottom of the foundation. The inner CMP  14  is then placed and positioned within the excavation  16  and the interior area  15  surrounded by the inner CMP  14  is partially backfilled along with the annular area  17  between the outer CMP  12  and the sidewall  19  of the excavation  16  to stabilize the CMPs generally in place within the excavation and relative to each other. Alternatively, a concrete plug  11  may be poured in the bottom of the inner CMP before backfilling as described in the &#39;947 patent. 
     According to the present invention, while installing the tower anchor bolt cage  18  inside the outer CMP  12 , a shear steel addition  40  is wrapped around the perimeter of the tower anchor bolt cage  18 , preferably about the lower one third of the pier foundation, to provide the pier foundation  100  with improved lateral shear resistance. According to a preferred embodiment, the assembled cage  18  is wrapped while being lowered, such as by a crane or the like, into the excavation  16 . The inner CMP  14  is then placed within the excavation, inwardly of the outer CMP and bolt cage, and a concrete plug  11  is poured in the interior area  15  at the bottom of the inner CMP to solidify its position. Cementitious material is then poured into the annular area  24  formed between the outer and inner CMPs and backfilling of the interior area  15  and annular area  17  with soil is completed. 
     The shear steel addition  40  may be made of hoop steel arranged in a plurality of loops vertically spaced between about three inches and about six inches apart, and preferably about four inches apart. When spaced about four inches apart, there are three loops per foot in the vertical dimension. This creates an angle from horizontal having a slope of about four inches over 14 feet. 
     The hoop steel is preferably one continuous strand although separate individual loops could be used with the understanding that installation would in most cases be more time consuming. The hoop steel strand is preferably either 0.5 inches or 0.6 inches in diameter and is high strength steel having a tensile strength on the order of 270,000 psi. 
     In vertical distance, the shear steel addition  40  as shown in  FIG.  2    covers a minimum of 10 feet around the bottom of the foundation. However, the lateral reinforcement provided by the hoop steel may extend upwardly more than the bottom one-third of the anchor bolt cage and even to the full vertical extent of the pier foundation to form a spiral hoop encasement  140  as will be discussed in connection with the embodiments shown in  FIGS.  3 - 5   . With a full vertical extent, the spiral hoop encasement  140  would cover a foundation of approximately 34 feet which is the current maximum vertical height of existing foundations of this type being constructed in the field. 
     The second embodiment of the present invention shown in  FIG.  3    includes a pier foundation generally designated by reference numeral  200  having a spiral hoop encasement  140  that covers substantially the entire vertical extent of the pier foundation  200 . As used herein, “substantially” is intended to cover spiral hoop encasements that cover at least 90% of the vertical extent, and preferably at least 95% of the vertical extent. The spiral hoop encasement  140  provides structural strength to the perimeter of the bolt cage  18  and eliminates the need for an outer CMP provided the surrounding sidewalls  19  of the excavation  16  are able to stand vertically when the hole for the foundation is drilled or excavated, such as in rock or stable soils. 
     The foundation  200  is constructed by drilling or excavating the hole  16 , placing an inner CMP  14  and partly backfilling the center area  15  as necessary to stabilize the CMP  14 . Alternatively, a concrete plug  11  may be poured to secure the inner CMP at the bottom. The tower bolt cage  18  is assembled outside the hole  16  and then wrapped with a spiral hoop encasement  140  while being lowered into the annular area  124  between the sidewalls  19  and the inner CMP  14 . Concrete is then poured into the annular area  124  and any remaining backfilling of the center area of the inner CMP  14  completed. Alternatively, the tower bolt cage may be lowered into the excavation  16  before the inner CMP  14  is placed and the plug poured, as with the first embodiment. In either case, i.e., regardless of the installation order of the inner CMP and the tower bolt cage, the second embodiment eliminates the need for the outer CMP  12 , reducing the cost of construction and also obviating the associated need to backfill with soil against the sidewall  19 . 
     A third embodiment of the pier foundation with lateral shear reinforcing loops of the present invention is shown in  FIG.  4    and generally designated by reference numeral  300 . The foundation  300  is suitable for installation in areas having rock or stable soil where the side walls  19  of drilled or excavated deep holes stand vertically. With such conditions, the excavation is formed as an annular trench  310  which is bordered by sidewall  19  and an inner sidewall  190 . The inner sidewall  190  defines the outer perimeter of a central area  115  which is constituted by the native soil which is not disturbed. With such a configuration, both the outer and inner CMPs are eliminated along with the need to backfill the inner CMP. In addition, the trench construction of  FIG.  4    also eliminates the need to form a concrete plug at the base of the pier to secure the inner CMP. 
     The foundation  300  is constructed by excavating the trench  310 , assembling the tower bolt cage  18  and wrapping the same with a spiral hoop encasement  140  while lowering the tower bolt cage  18  into the annular area  124  between the sidewall  19  and the inner sidewall  190 . Concrete is then poured into the trench  310 . By eliminating the need for both CMPs as well as the plug, and by saving the man and equipment hours otherwise needed for backfilling, the trench configuration shown in  FIG.  4    offers significant cost and time savings in construction. 
     A fourth embodiment of the pier foundation with lateral shear reinforcing loops according to the present; invention is shown in  FIG.  5    and generally designated by reference numeral  400 . Like the previous two embodiments, the foundation  400  is suitable for use in stable soils and rock where the sidewalls  19  stand vertical upon excavation. A cylindrical drill, hole  416  is excavated, a tower bolt cage  18  wrapped with a spiral hoop encasement  140  is positioned therein, and the entire hole  416  is filled with concrete. 
     The spiral hoop encasement  140  of each of  FIGS.  3 - 5    is made of one or more looped strands of high strength steel having the same structural parameters already discussed in connection with the shear steel addition  40  shown and described in connection with  FIG.  2   , The steel strands may be wound around the tower bolt cage while being pulled off of a roll of steel brought in by truck or other equipment to the construction site. Alternatively, individual loops may be installed with the the understanding that installation will generally take longer than with a continuous strand wound in spiral loops as has been described. The looped steel is preferably wire-tied or otherwise secured to the anchor bolts at appropriate intervals as the steel is wound around the tower anchor bolt cage to ensure that the loops remain in place and at the desired vertical spacing during concrete pour. 
     The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not limited by the dimensions of the preferred embodiment. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Father, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.