Methods for constructing tensionless concrete pier foundations and foundations constructed thereby
A tensionless concrete pier foundation for supporting a tower and a method of constructing the same is provided, the foundation having an outer CMP and an inner CMP with an annular space therebetween in which a plurality of sleeved tower anchor bolts are embedded, at least the outer CMP having an upper edge that is flush with the top of the foundation after the tower has been installed. A method of plumbing a tower anchor bolt cage using a bolt alignment ring is also provided that includes coupling the upper ends of the CMPs together with lateral spacing bolts that extend across the annular space. The tower anchor bolt cage is suspended from the lateral spacing bolts by the bolt alignment ring, and the lateral spacing bolts are shimmed on a low side as necessary for leveling the alignment ring and plumbing the bolt cage, before concrete pour.
1. A tensionless concrete foundation for supporting a tower, the tensionless concrete foundation comprising:
a concrete pier in an excavation, the concrete pier including an outer corrugated metal pipe (CMP) and an inner CMP having a smaller diameter than the outer CMP to define an annular space between the inner CMP and the outer CMP, the outer CMP having an upper edge and the inner CMP having an upper edge lower than the upper edge of the outer CMP, the annular space being filled with concrete, the outer CMP being filled with concrete above the annular space up to the upper edge of the outer CMP to form a concrete floor having an upper surface, and the outer CMP being positioned at a bottom of the excavation;
an upper set of lateral reinforcing and spacing bolts providing bursting steel resistance separately nutted adjacent outside the outer CMP and extending horizontally across the concrete floor above the inner CMP; and
a plurality of sleeved anchor bolts each having a lower end and an upper end, the plurality of sleeved anchor bolts being embedded in the concrete floor and the concrete in the annular space, the lower end of each sleeved anchor bolt being secured to an embedment ring adjacent a bottom end of the concrete pier, the upper ends of the plurality of sleeved anchor bolts extending upwardly to above a top of the tensionless concrete foundation, the top of the tensionless concrete foundation being defined as the upper surface of the concrete floor when fully grouted to be level with the upper edge of the outer CMP, the upper edge of the outer CMP thereby being flush with the top of the tensionless concrete foundation.
2. The tensionless concrete foundation of claim 1 , wherein the upper edge of the inner CMP is about one foot lower than the upper edge of the outer CMP.
3. The tensionless concrete foundation of claim 1 , further comprising a lower set of lateral spacer bolts separately nutted adjacent both inside the inner CMP and outside the outer CMP, respectively, and extending horizontally across the annular space.
4. The tensionless concrete foundation of claim 1 , further comprising a safety protection element covering the upper edge of the outer CMP.
5. The tensionless concrete foundation of claim 1 , wherein the concrete forming the concrete floor has a higher compressive strength than the concrete filling the annular space.