Concrete pier foundation with lateral shear reinforcing loops and methods of constructing the same
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.
1 . A pier foundation comprising:
a concrete pier formed in an excavation, the concrete pier including a plurality of sleeved anchor bolts embedded therein in an annular arrangement, the sleeved anchor bolts each having a lower end, and being secured together at their lower ends to form a bolt cage having an outer perimeter of the sleeved anchor bolts, the sleeved anchor bolts extending from adjacent a bottom of the pier foundation to above a top thereof, and a spiral loop flexible steel addition of an unrolled and windable continuous steel strand having opposing ends wrapped around the outer perimeter of the bolt cage and secured to the sleeved anchor bolts, individually, to provide lateral shear reinforcement to the pier foundation, and wherein the spiral loop flexible steel addition is wrapped around the outer perimeter of the bolt cage while the bolt cage is being lowered into the excavation, and
the excavation including at least an annular area filled with concrete in which the bolt cage wrapped with the spiral loop flexible steel addition is embedded, with the opposing ends of the spiral loop flexible steel addition being embedded in the concrete, wherein the excavation is configured as an annular trench having a center area of undisturbed native soil, the annular area being defined by an inner wall and an outer wall of the annular trench.
2 . The pier foundation according to claim 1 , wherein the spiral loop flexible steel addition extends over at least a bottom one-third of the bolt cage.
3 . The pier foundation according to in claim 1 , wherein the spiral loop flexible steel addition extends over substantially an entire vertical extent of the bolt cage.
4 . The pier foundation according to claim 1 , wherein the annular area is defined by an outer corrugated metal pipe and an inner corrugated metal pipe.
5 . The pier foundation according to claim 1 , wherein the annular area is defined by an inner corrugated metal pipe and a sidewall of the excavation.
6 . The pier foundation according to claim 1 , wherein the spiral loop flexible steel addition is hoop steel arranged in a plurality of loops vertically spaced between about 3 inches and about 6 inches apart.
7 . The pier foundation according to claim 6 , wherein the hoop steel is a continuous strand of high strength steel having a diameter of 0.5 inches or 0.6 inches and a tensile strength of approximately 270,000 psi.
8 . The pier foundation according to claim 1 , wherein the bolt cage includes an anchor ring adjacent the bottom of the pier foundation to which the lower ends of the anchor bolts are secured.
9 . The pier foundation according to claim 1 , wherein the spiral loop flexible steel addition is wound in loops around a perimeter of the bolt cage.
10 . The pier foundation according to claim 9 , wherein the loops are wound around at least a lower end of the bolt cage.
11 . The pier foundation according to claim 9 , wherein the loops are wound around substantially an entire vertical extent of the pier foundation.
12 . The pier foundation according to claim 1 , wherein the pier foundation includes a corrugated metal pipe and the bolt cage is positioned radially inwardly of the corrugated metal pipe.
13 . The pier foundation according to claim 1 , wherein the pier foundation includes a corrugated metal pipe and the bolt cage is positioned radially outwardly of the corrugated metal pipe.
14 . The pier foundation according to claim 13 , wherein the pier foundation includes a concrete plug formed within a bottom interior area of the corrugated metal pipe.
15 . The pier foundation according to claim 6 , wherein the loops have a vertical spacing that creates an angle from horizontal having a slope of about 4 inches to over 14 feet.
16 . A method of installing a laterally reinforced concrete pier foundation, said method comprising:
excavating an annular trench having a center area of undisturbed native soil, an annular area being defined by an inner wall and an outer wall of the annular trench;
assembling a tower anchor bolt cage having an outer perimeter including a plurality of sleeved anchor bolts in an annular arrangement, the sleeved anchor bolts each have a lower end and an upper end, and secured at their lower ends, the 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 annular trench; and
wrapping the outer perimeter of the tower anchor bolt cage with, and individually securing the sleeved anchor bolts to, a spiral loop flexible steel addition of an unrolled and windable continuous steel strand 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 annular trench; and
securing the wrapped tower anchor bolt cage with concrete after the wrapped tower anchor bolt cage is positioned within the annular trench with the lower ends of the sleeved anchor bolts at the bottom of the laterally reinforced concrete pier foundation, with the opposing ends being embedded in the concrete.
17 . The method according to claim 16 , wherein the wrapped tower anchor bolt cage is lowered into the annular trench, and the step of securing includes filling the annular trench with cementitious material.
18 . A pier foundation comprising:
a concrete pier formed in an excavation, the concrete pier including a plurality of sleeved anchor bolts embedded therein in an annular arrangement, the sleeved anchor bolts each having a lower end, and being secured together at their lower ends to form a bolt cage having an outer perimeter of the sleeved anchor bolts, the sleeved anchor bolts extending from adjacent a bottom of the pier foundation to above a top thereof, and a spiral loop flexible steel addition of an unrolled and windable steel strand having opposing ends wrapped around the outer perimeter of the bolt cage and secured to the sleeved anchor bolts, individually, to provide lateral shear reinforcement to the pier foundation,
the excavation being configured as an annular trench having a center area of undisturbed native soil, an annular area being defined by an inner wall and an outer wall of the annular trench, and
the annular area being filled with concrete in which the bolt cage wrapped with the spiral loop flexible steel addition is embedded, with the opposing ends of the spiral loop flexible steel addition being embedded in the concrete.