Static structures (e.g. – buildings) – Footing or foundation type – Concrete type
Reexamination Certificate
2002-02-08
2004-01-06
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Footing or foundation type
Concrete type
C052S292000, C052S297000, C052S223400, C405S244000, C405S256000
Reexamination Certificate
active
06672023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to concrete foundations, and more particularly, to reinforced concrete pier foundations useful for the support of tall, heavy and/or large towers which may be used to support power lines, communication systems, street lighting and signals, bridge supports, commercial signs, freeway signs, ski lifts and the like, and especially wind turbines which are subject to very high upset forces.
2. Background of the Invention
Various different forms of foundations utilizing some of the general structural and operational features of the instant invention have been known. However, these previously known foundations do not include some of the basic features of the instant invention. The combination of features incorporated in the disclosed embodiments of the instant invention enable a heavy duty foundation to be formed in situ or be precast and transported to the construction site, and be placed in position in a manner not requiring the use of large drilling rigs or pile drivers. The present invention is particularly useful in locations where the ground water is high and/or the depth clearance for placement of the foundation is low. The foundation of the present invention is capable of resisting very high upset loads and in a manner independent of the concrete of the foundation experiencing alternating localized compression and tension loading.
In a conventional concrete pier foundation the concrete bears the compressive loads and the contained reinforcing bars (rebar) are sized to bear the tensile loads. Anchor bolts are typically utilized solely for the purpose of attaching the supported structure to the foundation. The anchor bolts are typically placed within a reinforcing steel (rebar) matrix or cage using a removable template at the top and a separate anchor plate at the bottom of each bolt to prevent anchor bolt pullout. The entire module is poured in concrete. Conventional foundations typically resist overturning movement by their weight.
Further, when the foundation is loaded by the structure supported thereon, the foundation is subjected to varying tensile and compressive loads with there being a boundary at the bolt anchor plates where the loading on the concrete alternates from a compressive load to a tensile load depending upon the various forces on the supported structure. The tensile load from the overturning moment of the supported structure is applied near the top of the foundation by the anchor bolts and subjects the large portion of the foundation below the point of application to tension. The large foundation typically requires a great amount of reinforcing steel and a large amount of concrete to encase the reinforcing steel. Extensive labor is also necessary to assemble the reinforcing steel matrix and fill the volume of the foundation with concrete and fix the anchor bolts. A typical cylindrical foundation also requires the use of a large drill to excavate the hole.
My two prior U.S. patents, U.S. Pat. Nos. 5,586,417 and 5,826,387, hereby incorporated by reference in their entirety as if fully set forth, are hereinafter sometimes referred to as “my prior patents”. My prior patents disclose concrete pier foundations under high unit compression which eliminate the necessity for large quantities of reinforcing steel bars (rebar or tension bars) and substantially reduce the amount of concrete necessary. Therefore, the cost of these foundations is substantially less when compared to conventional designs. Furthermore, the foundations of my prior patents simplify the placement of the supported structure on the foundation and eliminate alternating cyclical compression and tension loading on the foundation, thereby substantially reducing fatigue. Also, these patented foundations allow for the replacement of the tower anchor bolts in the unlikely event of bolt failure and allow for removal of the upper four to five feet of the foundation in the event such action is desired for decommissioning purposes.
The foundations of my prior patents are preferably in the shape of a concrete cylinder. The outer boundary shell of the concrete may be formed by corrugated metal pipe (CMP). The inner boundary, preferably in large hollow cylinder foundations, also may be formed by CMP of a lesser diameter. Elongated high strength steel bolts are positioned around the periphery of the concrete cylinder and extend from a peripheral anchor plate or ring near the bottom of the cylinder vertically up through the concrete portion of the foundation to a peripheral connecting plate or flange adjacent the upper end of the structure. The bolts are received in “hollow tubes” to isolate the bolts from the concrete. The steel bolts preferably serve as anchor bolts for attachment of the base flange of the supported tower structure, and the anchor bolt pattern may thus be determined by the bolt hole pattern on the lower base plate or flange of the supported tower. The steel bolt pattern may also be engineered into the construction of the foundation by a removable template.
The “hollow tubes” are preferably elongated plastic tubes or sleeves which encase the bolts substantially through the entire vertical extent of the concrete and prevent the bolts from adhering to the concrete. Then, the bolts can be tensioned after the concrete has hardened and cured in order to post-tension the entire concrete foundation. Alternatively, the elongated bolts can be wrapped in plastic tape, or otherwise sheathed to prevent the bolts from adhering to the concrete during curing and allow the bolts to stretch under tension over the entire operating length of the bolt through substantially the full vertical extent of the concrete. There is typically no conventional rebar reinforcing steel in the foundation, except perhaps in large foundations where a small amount of incidental rebar may be used to stabilize the bolts during construction of the foundation.
The center of a large hollow cylindrical foundation according to my prior patents is filled with excavated soil and then capped. Excavation for the foundation may be done using widely available, fast, low cost excavating machines instead of relatively rare, slow, costly drills necessary for conventional cylindrical foundations.
The foundations of my prior patents use the mechanical interaction with the earth to prevent overturning instead of the mass of the foundation typically used by other foundations for turbine towers and other large structures subject to high upset forces. The high strength anchor bolts are tightened to provide heavy tension on the foundation from a heavy top flange through which the bolts pass to the anchor flange or plate adjacent the bottom of the foundation, thereby post-stressing the concrete in great compression and placing the entire foundation, between the heavy top plate or flange and lower anchor plate or flange, under high unit compression loading. The bolts are tightened so as to exceed the maximum internal tension expected from overturning forces of the tower structure on the foundation. Therefore, the entire foundation withstands the various loads with the concrete thereof always remaining in compression and the bolts always in static tension. The concrete pier foundations of my prior patents may be formed in situ in a remote location or be formed in a precast concrete section placed under heavy compression.
To describe a portion of the foundation structure incorporated in the foundation of the present invention, reference is now made to
FIGS. 1
,
2
and
2
A which are taken from my prior patents. In these Figures, the numeral
10
generally designates the pier foundation. The foundation
10
includes inner and outer upstanding corrugated metal pipe (CMP) sections
12
and
14
. The outer section
14
is initially placed within a hole or excavation
16
formed in the ground
18
and rests upon the bottom of the excavation
16
. The inner section
12
is then placed and positioned within the excavation
16
. The interior of the inner CMP
12
is partially back filled a
Friedman Carl D.
Jacobson & Holman PLLC
Nguyen Chi Q.
LandOfFree
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