Static structures (e.g. – buildings) – Cast in situ composite slab
Reexamination Certificate
2001-10-26
2002-10-29
Canfield, Robert (Department: 3635)
Static structures (e.g., buildings)
Cast in situ composite slab
C052S223600
Reexamination Certificate
active
06470640
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a reinforced concrete building structure, and more particularly to such structure as comprising a shrinkage compensating concrete wherein active expansive and shrinkage forces accumulate to the peripheral portion of the slab additively further from its centroid. The reinforcing bars are restricted to the peripheral portion and are aligned with the expansive and shrinkage forces.
Shrinkage compensating concrete is often referred to as “self-stressing concrete” and to “chemically prestressed concrete.” Unlike traditional Portland cement based concrete, the shrinkage compensating concrete has a constituent that actively causes the concrete to volumetrically enlarge. The American Concrete Institute, ACI, defines shrinkage compensating concrete as “a concrete that, when strained by reinforcement or other means, expands . . . [and] ideally, a residual expansion will remain in the concrete, thereby eliminating shrinkage cracking.” The restraint of shrinkage compensating concrete is elemental to its function.
Unlike prestressed concrete and post-tensioned concrete where the concrete is passive and the restraint actively acting upon the concrete from either pre- or post-tensioning the reinforcement, shrinkage compensating concrete generates its own expansive forces which, in turn, tension the reinforcement. ACI expounds on restraint as “a resilient type of restraint, such as that provided by internal reinforcement shall be provided to develop shrinkage compensation. Other types of restraint, such as adjacent structural elements, sub-grade friction, and integral abutments are largely indeterminate and provide either too much or too little restraint.”
While industry guidelines are definitive about the amount of reinforcement required to restrain shrinkage compensating concrete slabs, by way of an amount of steel by cross-sectional area of concrete, the configuration of restraint is left largely to the specifier, except to recommend wire mesh and deformed reinforcing bar, two-way reinforcement, parallel and perpendicular to any given side of the slab.
Related technology as set forth in prior art patents are for passive concrete and active compression. Thus, the reinforcements of prior art reinforced concrete slabs are purposed for imposing an externally generated force upon a shrinking concrete. More specifically, U.S. Pat. No. 1,559,837 relates to prestressing a wheel frame on posts so as to generate a compressive force against the concrete.
U.S. Pat. No. 2,035,007 provides a structure in which the rotation of the stress is primarily of a general master rotation within which there is auxiliary rotation of subdivided circular areas producing circumferential stress bands area alternating between compressive stresses in the alternative bands.
U.S. Pat. No. 3,036,356 discloses a method of producing prestressed concrete slabs by perimeter and diagonal bands of pretensioned cables acting in concert upon a traditional concrete.
U.S. Pat. No. 3,222,835 discloses prestressing concrete by producing unique stresses between a central area and the peripheral of the slab. The stress is along a radial cable system and intended to provide concentric force.
U.S. Pat. No. 3,513,609 discloses a post-tensioning concrete for developing a concentric compressive force.
U.S. Pat. No. 3,710,526 discloses pre-tensioning concrete to develop compressive force, an annular compressive beam, inside a slab by a radial ring of tensioning cables.
U.S. Pat. No. 3,455,069 discloses a roof structure comprised of a traditional concrete with two interconnected tension rings connected by radial tension bars. The resultant self-supporting, self-resistant traditional loads roof structure relies upon rings to impose force by means of connected radial tension bars.
U.S. Pat. No. 4,432,175 discloses a slab having an internal post-tensioning cable about its centroid. The cable, however, relies upon an external force applied to the cable able to slip inside of a sheath.
U.S. Pat. No. 5,283,996 discloses an interlocking ground cover where a prestressed concrete slab is made by relying upon a molding frame assembly comprised of posts including a central ring and diagonal tensioning reinforcement.
U.S. Pat. No. 5,875,595 discloses a post-tensioning system for a prefabricated building panel where a slab is peripherally and centrally confined by a single post-tensioning cable of sufficient diameter and tensioning force to essentially apply a concentric compressive force.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide bar reinforcement for a shrinkage compensating concrete slab with the reinforcing bars aligned with the expansion and shrinkage forces normally concentrated in the peripheral portion of the slab to thereby elastically restrain the forces acting as an internally developed tension ring and to maximize the efficiency of the reinforcement.
In carrying out this objective, a plurality of non-post-tension and non-pre-tensioned, deformed reinforcing bars are embedded within the concrete slab and are restricted to the peripheral portion of the slab such that the centroid slab portion is completely devoid of any reinforcement bars.
The reinforcing bars are uniformly spaced apart and lie in an array of many possible configurations, such as concentric circles, radiating bars, a combination of radiating bars and concentric circles, concentric rectangles, concentric rectangles having chamfered corners, bars lying parallel and perpendicular to one another, etc.
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Canfield Robert
Dykema Gossett PLLC
Kalman Floor Company
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