Patent Grant
8910434
This invention relates to a concrete stair that is pre-cast, an adjustable mold for casting stairs of different widths, and a method of casting such stairs.
Conventional pre-cast concrete stairs exhibit a number of disadvantages. Very often, such stairs are constructed in a form or mold that has a step-shaped bottom surface for defining the steps and an open upper end into which the concrete is poured. This form creates a stair that has a heavy flat slab along its bottom surface. Such a stair requires unnecessarily large amounts of concrete and is quite heavy. It requires a large crane to lift the stair into place. It is challenging to workers to place the heavy stair into the stairwell. Transportation of such stairs to the construction site is also expensive because of the limited number of stairs that can be transported on one truck. The landings or other support structures for holding these pre-cast stairs in position also have to be made stronger because of the weight of the stairs. This requires more concrete or other type of reinforcement material to support the stairs than is desirable.
One of the most common uses of concrete stairs is in the stairwells of large buildings to provide a fire escape. Building owners want to keep these stairs as narrow as possible to limit the size of the stairwell, which is nonproductive space. This is difficult because of the requirement that the stairs have rails.
Because of different building requirements and designs, stairs of different step widths are frequently required to be cast. The present forms for pre-casting concrete stairs cannot be adjusted to match varying widths of the stairs. A completely new form is required for each variation in stair width, which adds to the cost of casting stairs.
Concrete stairs can be cast in several sections and then put together at the building site. However, this approach suffers from the disadvantage of being highly labor intensive.
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Prior art pre-cast concrete stairs are heavy structures because the structural support is in the steps themselves which must not have any point that is weaker than what is necessary to support the entire stair. The stair itself is the beam and like any beam must have the same strength throughout its entire length, including all sections of each step. This results in the use of a lot more concrete and reinforcing material than would be required in just the steps to support the human traffic. The massive size of the prior art stair is visually apparent in
This invention provides a lightweight pre-cast concrete stair, ideally suited for use as the fire stairs in a multi-story building. This stair is constructed with two beams that are cast with the stair steps as an integral monolithic structure. One of the beams, the integral down edge beam, projects below the steps on one side of the stair and does not impinge upon the width of the steps. The steps on this side of the stair serve as the top of the beam. This integral down edge beam is designed to be placed against a wall of the stairwell. The second beam, an integral up edge beam, projects above and to the side of the steps and is located on the other side of the stair. Lightweight steps are suspended between these two beams. These steps can be constructed with much less concrete and are consequently much lighter than the steps of prior art concrete stairs because the steps do not serve as a beam. The weight of the stairs, including traffic on the steps, creates compression on the tops of the integral down edge beam and integral up edge beam, and tension on the bottoms of the integral down edge beam and integral up edge beam, which enhances the combined strength of the beams. The asymmetric orientation of the members creates a stronger cross-section than if the beams were in the same plane horizontally, allowing greater load handing capability. Stairs of this type require significantly less concrete than a prior art stair to handle the same load conditions. An unusually strong lightweight stair can be pre-cast using the molds and methods of this invention. This use of a tension beam as an integral up edge beam and a compression beam as an integral down edge beam enables the saving of 45 to 50% of the concrete needed to construct a prior art concrete stair of the same size.
Because of different size and design parameters of buildings and the fact that builders want to conserve the space dedicated to a stairwell in a building, stairs of different widths are frequently required. In the past it was necessary to have a different form for every width of stair. This invention provides an adjustable mold for pre-casting these monolithic stairs of varying widths. The width of the mold for the stairs can be easily adjusted to cast stairs of varying widths. A new method is provided for casting the monolithic stair of this invention in different widths without changing forms.
One other problem involved in casting stairs is the mistakes involved in laying out the reinforcing rods in the mold. The mold of this invention can be provided with hooks or other means to locate and hold the reinforcing rods in proper position during the pouring of concrete, which makes it much more difficult to make a mistake. A mistake in laying out the reinforcing rods could compromise the strength of the stairs.
The stair of this invention is illustrated in
The stair 10 of this invention is designed for the placement of the stair 10 with the integral down edge beam 14 adjacent to a wall. Since portions of the treads 16 and 18 and risers 20 on this side 32 of the steps 28 of the stair 10 form the top of beam 14, this placement allows for more tread room on the stair 10. This allows for people to have more room to walk on the stair. This is especially important in the evacuation of a building during an emergency, such as a fire. There obviously would be less stair room if the integral up edge beam 12 were placed against the wall. The integral up edge beam 12 prevents items from rolling off of the stairs and hitting people below.
This stair 10 may have a handrail. Cuts may be provided in the top 24 of the integral up edge beam 12 for the attachment of a handrail (not shown). Cast-in nosing can be provided with groves to help prevent people's feet from slipping on the stair.
The tremendous savings in concrete in forming the individual steps, illustrated by the numeral 28, of the stair 10 of this invention can be shown by examining
The depth of the “throat” of the stair 10 is illustrated by line B-B1 between the underside 22 of the stair 10 and the top 26 of the tread 16 where it meets the riser 20 as illustrated in
This stair 10 may be placed directly on the top surface of a landing (not shown) or it may have a load transfer device (not shown), which can be placed in the mold 30 for molding. When the top of the stairs 39 is placed in position the load transfer device can be placed in a support rest in the landing (not shown). A similar load transfer device can be placed at the bottom of the stairs, or the stairs 10 can simply rest on the landing.
Referring again to
Because this mold is reusable can be used to cast stairs of different widths. The mold is preferably constructed from steel. However the same principles for the mold would apply if other materials are used. It has been found that steel is more durable for repeated casting of stairs and for being adjusted to cast stairs of different width. The up edge beam 12 is shown in the mold 30 in
The width of the stairs 10 can be adjusted by moving the adjustable outside mold wall 56 for the down edge beam 14. It can be moved either to the right or the left depending on the width of the stairs desired. A number of mechanisms may be used for moving this wall. The means illustrated in
These stairs may need to be reinforced. The mechanism for putting in the reinforcement rods reduces the possibility of risks of misplacement in that regard. Reinforcing bars 68 and 70 are shown in
The concrete can be poured into the mold and allowed to set to form an integrated monolithic structure. An insert for each tread is placed in the proper position in the mold before pouring the concrete. After the stairs have been molded and cured, they may be removed and installed in a building or a structure. By using the mold and molding process of this invention a lightweight, strong stair can be pre-cast. As these stairs are lifted into place by cranes the weight saved by these stairs not only results in a tremendous reduction in the amount of concrete used but also makes it easier to lift the stair by a crane, and increases the height at which pre-cast stairs may be used. In mid or high rise buildings, pre-cast stairs are currently not an option because of the weight of prior art pre-cast stairs. When concrete stairs are required, due to the owner's preference, fire code, or building code requirements, only cast-in-place stairs, which are highly labor intensive, are currently available.
It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.
This application claims the benefit of and priority to U.S. Patent Application Ser. No. 60/866,686, filed on Nov. 21, 2006, entitled “EDGE BEAM STAIR” which is incorporated herein by reference.
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| Number | Date | Country | |
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| 20080115429 A1 | May 2008 | US |
| Number | Date | Country | |
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| 60866686 | Nov 2006 | US |
