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

Abstract

A concrete pier foundation having a plurality of sleeved tower anchor bolts embedded therein and a spiral loop encasement providing lateral shear reinforcement is provided. The spiral loop encasement surrounds at least a lower portion of the concrete pier and is formed by hoop steel wrapped around the perimeter of the tower anchor bolt cage. In proper soils or rock the spiral loop encasement can eliminate the need for corrugated metal pipes, reducing the cost and complexity of construction.

Claims

1. A method of installing a laterally reinforced concrete pier foundation comprising: excavating a hole; assembling a tower anchor bolt cage having an outer perimeter including a plurality of sleeved anchor bolts in an annular arrangement, said sleeved anchor bolts each have a lower end and an upper end, and secured at their lower ends, said lower ends being adjacent a bottom of the laterally reinforced concrete pier foundation with the upper ends of the sleeved anchor bolts extending above a top of the laterally reinforced concrete pier foundation when the tower anchor bolt cage is placed within the hole; and wrapping the outer perimeter of the tower anchor bolt cage with, and individually securing the sleeved anchor bolts to, a spiral loop steel addition having opposing ends over at least a lower end thereof to produce a wrapped tower anchor bolt cage and provide lateral shear reinforcement to the laterally reinforced concrete pier foundation; positioning the wrapped tower anchor bolt cage within the hole; and securing the wrapped tower anchor bolt cage with concrete after said wrapped tower anchor bolt cage is positioned within the hole with the lower ends of the sleeved anchor bolts at the bottom of the laterally reinforced concrete pier foundation, wherein the opposing ends are embedded in the concrete; wherein the step of excavating the hole includes digging an annular trench with undisturbed native soil forming a center area encircled by said trench, the wrapped tower anchor bolt cage being lowered into said trench and said step of securing including filling the trench with cementitious material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a concrete pier foundation like that disclosed in the '417 patent.

(2) FIG. 1A is a cross-sectional view of the upper end of the pier foundation shown in FIG. 1.

(3) 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.

(4) 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.

(5) 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.

(6) 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

(7) 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.

(8) A concrete pier foundation like that disclosed in the '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. 1A, 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 '417 and '947 patents for a more detailed description of the structure and construction of the basic pier foundation 10 shown in FIG. 1.

(9) 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 '417 and '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 '947 patent.

(10) 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.

(11) 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.

(12) 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.

(13) 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.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) 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.

(19) 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.

(20) 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.