Fire escape – ladder – or scaffold – Wall- or floor-attached – Independent rung or step
Reexamination Certificate
1998-08-20
2001-11-13
Lev, Bruce A. (Department: 3634)
Fire escape, ladder, or scaffold
Wall- or floor-attached
Independent rung or step
C182S090000, C052S020000, C052S184000
Reexamination Certificate
active
06315077
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to manholes and manhole steps and ladders.
BACKGROUND OF THE INVENTION
Pre-cast concrete manholes are widely used throughout the world to provide access to storm and sanitary sewer systems and a variety of other below-ground installations of piping, cables and the like. If such access is to be used, a ladder or steps must be provided to permit workers to descend into and climb out of the manhole. A variety of structures have been employed to make this possible, including ladders temporarily positioned in the manholes and ladders or steps permanently attached to the inside wall of the manholes.
One highly successful such step is disclosed in U. S. Pat. No. 4,100,997, which is incorporated herein by reference. U. S. Pat. No. 4,100,997 describes a steel reinforced plastic step that is injection molded of copolymer polypropylene. Support members that terminate in ends having molded, deformable annular projections are driven into pre-formed holes in the inside wall of the manhole.
In order to use a step of the type described in U. S. Pat. No. 4,100,977, holes must be formed in the inside face of the manhole having the proper size, location, orientation and spacing to receive the step legs. This has conventionally been accomplished by inserting metal rods or other forms from inside the form through appropriately located holes in the inner wall of the manhole form, so that properly shaped and located holes will be formed in the concrete manhole. Such hole-forming rods must also be withdrawn from inside the form before the formed concrete manhole and the form are separated. Doing so is time-consuming and arduous because it typically requires that a worker climb inside of the inner manhole form, which is difficult and unpleasant to do. Accordingly there is a need for a better method of forming holes in pre-cast manholes to receive steps.
Manholes frequently are manufactured with a plastic liner that forms the inside of the manhole and protects the concrete from chemicals that potentially would damage the concrete. Manufacture of manholes with such liners presents additional challenges to the provision of steps despite the presence of the liner and without breaching the protective layer it provides. For example, step holes may be drilled into the formed manhole, but some form of liner or other sealant must then be inserted into the step hole. Alternatively, the liner may be manufactured with deep indentations which act as step holes; however, such indentations may substantially increase the cost of the mold used to form the liner.
SUMMARY OF THE INVENTION
This invention is a frangible insert with plug and sleeve portions that is inserted in a prepositioned bushing in the wall of a manhole form from the convex, easily reached side of the inner form wall. A key in the sleeve portion is received in a keyway in the bushing in the form wall so that the insert is properly oriented in the form. Concrete is then poured into the form, enveloping and affixing the plug portion within the manhole wall.
The insert is manufactured of plastic or other suitable materials. A weakened, frangible region is provided on the sleeve in a position immediately adjacent to the form wall so that after the concrete is cured, the manhole and form can simply be separated, causing the plug portion, which is embedded in the concrete, to separate from the insert portion in the form bushing. Nothing needs to be removed before separating the form and cured manhole, with a consequent diminution in necessary labor by simplification of the insert insertion process and elimination of the need to remove a hole-forming component before separating the cured manhole and the form.
If the manhole is lined, the liner is positioned in the form on the outside surface of the inner form wall. Holes in the liner may be pre-formed or drilled or cut to coincide with the bushing on the inner wall. The plug portion of the insert is then positioned through each bushing and against the liner and plastic welded or otherwise affixed to form a tight seal between the insert and the liner. Alternatively, the plug insert may be plastic welded or otherwise affixed to the interior (concrete side) or the liner in the appropriate locations. The liner may then be penetrated to allow steps to be inserted into the insert. The liner may be penetrated before of after pouring and curing of the concrete.
Accordingly, it is an object of the present invention to provide an insert for forming step holes in a manhole that need not be removed after the manhole is formed.
Another object of the present invention is to provide an insert for forming step holes in a manhole having a frangible portion used to position the insert in the manhole form in which the frangible portion automatically separates from a hole-forming plug when the manhole form is separated from the manhole.
A further object of the present invention is to provide an insert for forming step holes in a lined manhole that prevents materials in the manhole from contacting the concrete protected by the liner.
Other objects, features, and advantages of the present invention will become apparent with reference to the remainder of the written portion and the drawings of this application, which are intended to exemplify and not to limit the invention.
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McInvale Charles W.
Peacock Bobbie D.
Dixon, Esq. Michael K.
Kilpatrick & Stockton LLP
Lev Bruce A.
M. A. Industries, Inc.
Pratt, Esq. John S.
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