Static structures (e.g. – buildings) – With indicia
Reexamination Certificate
1999-05-12
2002-07-30
Kent, Christopher T. (Department: 3635)
Static structures (e.g., buildings)
With indicia
C052S223100, C052S511000, C052S512000
Reexamination Certificate
active
06425212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of safety warning devices and systems for construction, commercial and residential sites. More particularly, the present invention relates to warning devices and systems for warning construction workers, commercial building owners and home improvers of the dangers inherent in certain types of concrete slabs.
2. Description of the Related Art
Concrete, as used in the construction industry, is a mixture of one or more inert aggregate materials, a binding material such as portland cement, and water. The mixture is cast into a formwork, generally a wooden mold which holds the concrete during the pouring and curing stages. The slurry mixture then cures, hardening by a chemical reaction. In this manner, a cast concrete member of uniform thickness is produced. This cast member is generally referred to as a concrete slab.
Concrete alone is inherently incapable of resisting tension. For that reason, steel reinforcing is used to strengthen concrete. Reinforcing steel bars are known in the industry as rebars. These rebars reinforce the concrete by imparting the tensile characteristics of the reinforcing steel to the concrete. Thus, the bond between the concrete and the rebars must be sufficient to keep them from being pushed or pulled out of the slabs.
In unstable areas, and in situations where high loading tensions are expected, a stiffer beam is desired. For that reason, design and safety considerations often dictate the use of prestressed or post-tensioned concrete slabs. In such slabs, the presence of pre-applied compressive stresses in the tension region of a beam prior to normal loading will cause the beam to undergo less deflection once the intended load is applied. In other words, prestressing or post-tensioning concrete slabs produces stiffer beams. These stiffer beams greatly increase stability and safety of the structures erected therewith. Alternatively, smaller beams can be employed in place of larger and weaker ones, thus reducing both the cost and weight of the structures constructed.
In both prestressed and post-tensioned concrete slabs, steel tendons are laid down within the beam prior to pouring and curing of the concrete slab. In prestressed concrete slabs, tension is applied to the steel tendons prior to pouring and curing the slab. This is done by attaching the steel tendons to anchors and applying tension thereto. The concrete mixture is then poured within the formwork, and the concrete slab allowed to cure. The steel tendons are then severed, thereby transferring the tension to the concrete. In post-tensioned concrete slabs, the formwork is built with tubes running from end to end. The steel tendons are then inserted within the tubes, and the concrete poured. After the concrete cures, a desired tension is applied to the steel bars within their respective tubes. The tubes are then filled with, for example grout, or the terminal portions of the tendons are anchored to the slab in some manner. Alternatively, greased tendons may be used, the grease coating preventing the steel tendons from bonding to the concrete as it cures.
The tensions applied to the steel tendons, in either the prestressed or post-tensioned situations are great, on the order of tens of thousands of pounds of force. Tensioning forces on the order of 20,000 lbs. are typical. While this tensioning produces a stiff slab of concrete well suited to high stress building situations, use of pre or post-tensioned concrete slabs is not without dangers.
In particular, if the bond between the concrete and the steel tendons is reduced somehow, there exists the real danger that the forces applied to them will catastrophically release in an unintended manner. Alternatively, if the structural integrity of the steel tendons is compromised in any manner, the forces applied to the steel tendons can cause them to shoot out of the concrete slabs with great force. This can happen, for example, if the prestressed or post-tensioned concrete slab is drilled, or in any way penetrated, and the drill bit or penetrating element encounters one of the highly tensioned steel tendons. This can also happen if nails or bolts are driven into a pre or post-tensioned slab of concrete. The steel tendons can then whip unexpectedly out of the concrete slab with a force nearly equal to that applied to them when the slab was formed. The violent release of these tensioned steel tendons has been known to injure and kill people and damage property.
Thus, construction workers, homeowners, or commercial building owners who are unaware that tensioned concrete slabs have been used in their site, building or home are in grave danger of a potentially fatal injury should they, for any reason, drill, nail, drive a bolt into or through, or in any way penetrate the prestressed or post-tensioned concrete slabs. Even penetrating one inch in such slabs is highly dangerous, as the tensioning steel tendons often come to within an inch of the surface of the slab.
What is desired is a means for warning construction workers, commercial building owners, homeowners and all others of the presence of prestressed or post-tensioned concrete slabs within their job site, building or homes.
Conventional devices and methods are known which indicate the location of various electrical, communications and structural members embedded within cement or concrete slabs. One such device is disclosed in U.S. Pat. No. 2,854,840 to Anderson.
Anderson discloses a wire comprising a number of magnetic markers attached thereon. The wire and magnetic markers are embedded within cement floors and indicate the presence of power or communications lines therein. However, a compass is needed to detect these magnetic markers, rendering them invisible to the unaided eye. They are, as such, poorly suited as indicating or warning devices to warn, for example, construction workers at a job site of the presence of potentially dangerous prestressed or post-tensioned concrete slabs.
Another approach was taken by Bates, as disclosed in U.S. Pat. No. 5,003,735. In Bates, resilient fibers project from the surface of a poured concrete surface to indicate the presence of, for example, power lines, to help in locating potential electrical outlets. The resilient nature of the projecting fibers allows them to resiliently yield upon engagement by means employed in finishing the outer surface of the concrete or cement slab. It is apparent that these fibers, although resilient, will interfere with the various polishing processes used in finishing concrete or cement slabs. Indeed, these resilient fibers could get caught in the polishing machine, thus causing delays and further costs.
Palmer, in U.S. Pat. No. 1,531,754, discloses a device wherein an inscription plate is fastened to a concrete slab by inserting a bolt through a plate-and-anchor combination previously imbedded in the cement.
In the approach taken by Haggenjos in U.S. Pat. No. 1,624,048, an anchor is cast into the concrete and an inscription plate is applied afterward.
The devices set forth by Palmer and Haggenjos are not flush with the concrete surface and would not be suitable for prestressed or post-tensioned concrete slabs, as the outward projection of a bolt, plate, or other parts could interfere with the polishing of the concrete. Additionally, inserting a fastener into an anchor of unspecified length, such as described by Palmer, could cause the anchor to press outward and into the slab, creating just the kind of hazard which it is desired to avoid.
Kramer et al., in U.S. Pat. No. 4,979,462, disclose a device and a method for indicating the location and direction of various structural members in concrete members. In said patent of Kramer et al., an indicator device is disclosed which spans the width of the concrete slab, the indicator device having both top and bottom indicators. The disclosed indicator assembly consists of a post having a length substantially equal to the width of the concrete slab, the post supporting, at its extremities, the to
Chaikin Douglas A.
Kent Christopher T.
Peninsula IP Group
LandOfFree
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