TREAD MOUNTING SYSTEM FOR SPIRAL STAIRCASE

Abstract

A method is disclosed of attaching a tread assembly of a spiral staircase to a vertical support column. One step of the method involves providing a tread assembly having a tread portion attached to an arcuate mounting plate defining at least one hole through which extends a fastener defining external threads, the mounting plate having a first face defining a first radius of curvature. Another step involves providing a support column extending along an axis, the support column having a plurality of axially and angularly spaced apart tread attachment locations, each of the tread attachment locations having an arcuate outer surface defining a corresponding aperture for receipt of the fastener, the arcuate outer surface defining a second radius of curvature that is greater than the first radius of curvature. According to another step of the method, the tread assembly is loosely connected to one of the tread attachment locations of the support column. According to another step, the fastener is tightened such that the arcuate mounting plate of the tread assembly is elastically deformed to be in substantial engagement with the tread attachment location and applies tension to the elongate fastener to inhibit loosening thereof.

Claims

1. A method of attaching a tread assembly of a spiral staircase to a vertical support column, said method comprising steps of: (a) providing a tread assembly having a tread portion attached to an arcuate mounting plate defining at least one hole through which extends a fastener defining external threads, said mounting plate having a first face defining a first radius of curvature; (b) providing a support column extending along an axis, said support column having a plurality of axially and angularly spaced apart tread attachment locations, each of said tread attachment locations having an arcuate outer surface defining a corresponding aperture for receipt of said fastener, said arcuate outer surface defining a second radius of curvature that is greater than the first radius of curvature; (c) loosely connecting said tread assembly to one of said tread attachment locations of said support column; and (d) tightening said fastener such that said arcuate mounting plate of said tread assembly is elastically deformed to be in substantial engagement with said tread attachment location and applies tension to the elongate fastener to inhibit loosening thereof.

2. A method as in claim 1, wherein said at least one elongate fastener comprises a plurality of bolts with corresponding nuts and said at least one hole comprises a plurality of holes, each of said bolts extending through a corresponding one of said plurality of holes defined in said mounting plate.

3. A method as set forth in claim 2, wherein each of said bolts comprises a carriage bolt having a square neck portion adjacent to an enlarged head.

4. A method as set forth in claim 3, wherein said corresponding aperture for each of said carriage bolts is configured as a keyhole defining an enlarged portion sized to receive the head of the carriage bolt and a reduced width slot extending from the enlarged portion for slidably receiving a square neck of the carriage bolt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A full and enabling disclosure of the present invention, including the best mode thereof directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which:

[0013] FIG. 1 shows a perspective view of a portion of a spiral staircase in accordance with the present invention;

[0014] FIG. 2 is a bottom perspective view of a tread assembly of the spiral staircase as shown in FIG. 1;

[0015] FIG. 3 is a partial perspective view of a reverse side of a portion of the tread assembly as shown in FIG. 2;

[0016] FIG. 4 is a partial perspective view of a portion of a support column of the spiral staircase in FIG. 1 that shows mounting keyholes for attaching a tread assembly to the column;

[0017] FIG. 5A is a diagrammatic representation in a horizontal plane of the column and a mounting plate of the tread assembly as in FIG. 1, illustrating respective radii;

[0018] FIG. 5B illustrates the column and the mounting plate as in FIG. 5A, with the mounting plate in an unstressed state prior to attachment to the column; and

[0019] FIG. 5C illustrates the column and the mounting plate as in FIG. 5A, with the mounting plate in a stressed state once attached to the column to inhibit loosening of the attachment hardware.

[0020] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0022] As used herein, terms referring to a direction or a position relative to the orientation of a spiral staircase, such as but not limited to vertical, horizontal, above, or below, refer to directions and relative positions with respect to the spiral staircase orientation in its normal intended operation, as indicated in FIG. 1.

[0023] Further, the term or as used in this disclosure and the appended claims is intended to mean an inclusive or rather than an exclusive or. That is, unless specified otherwise, or clear from the context, the phrase X employs A or B is intended to mean any of the natural inclusive permutations. That is, the phrase X employs A or B is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles a and an as used herein and the appended claims should generally be construed to mean one or more unless specified otherwise or clear from the context to be directed to a singular form. Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of a, an, and the may include plural references, and the meaning of in may include in and on. The phrase in one embodiment, as used herein does not necessarily refer to the same embodiment, although it may.

[0024] Referring now to FIGS. 1 and 2, a spiral staircase 10 includes a vertically oriented, hollow cylindrical column 12 onto which tread assemblies 14 attach. Each tread assembly 14 includes a tread portion 15 and a mounting plate 30. In this case, tread portion 15 is fabricated at least in part from sheet metal and includes a horizontal, generally planar step portion 16 that has edges extending radially from the column so that portion 16 has a wedge (i.e., fan) shape. An outer edge of portion 16 has an arcuate curve with a radius that is equal to the edge's radial distance from the center axis A of column 12. With particular reference to FIG. 2, vertically planar side flanges 18 extend downward from the radially extending edges of step portion 16 along the entire respective radial edge's length, and tabs 19 bend inward (i.e., toward each other) from edges of respective side flanges 18 opposite column 12 and extend below the arcuate outer edge of portion 16. Each tab 19 has a through-hole 24 that provides an attachment point for mounting hardware to attach a guardrail and handrail weldment assembly (not shown). Side flanges 18 have a trapezoidal profile so that the proximal edge nearer the column is longer than the opposite distal edge. A pair of hollow reinforcement tubes 20 have vertically elongated rectangular cross sections and attach via welding below step portion 16, extending the entire radial distance along each corner where step portion 16 meets a respective side flange 18 to thereby provide rigidity to the tread. Each reinforcement tube 20 has a proximal cutout 22 that provides access to carriage bolts and nuts, discussed below.

[0025] Each tread portion 15 attaches via weldment to an arcuate mounting plate 30 that has a curvature so that it defines a portion of a hollow cylinder. Mounting plate 30 defines two vertically offset through-holes that receive respective carriage bolts 36. Referring to FIGS. 3 and 4, carriage bolts 36 include an enlarged domed head 36a, square neck portion 36b, and threaded shank 36c. Column 12 has a plurality of tread attachment locations each defining a pair of vertically offset keyholes 40 for tread assembly mounting that are spaced to match the spacing of holes 34 in mounting plate 30. Each pair of keyholes 40 is spaced axially with respect to the next upper or lower keyhole pair to provide a selected step height. The keyhole pairs are also rotationally offset (i.e., angularly spaced) about the column's axis so that each step partially overhangs a respective adjacent tread below and the spiral arrangement is provided.

[0026] Keyholes 40 each include an enlarged circular portion 40a that is sized to receive head 36a and a reduced width slot portion 40b with a width that is large enough to receive square neck portion 36b of carriage bolt 36 when opposite flat sides thereof are aligned with the sides of the slot. Slot portion 40b is narrow enough that the square neck portion cannot significantly rotate about the bolt's axis of elongation when disposed within the slot. With this configuration, tread assemblies 14 may be mounted and fastened to column 12 (FIG. 1) from a single side of column 12. That is, keyholes 40 receive respective carriage bolts 36 that are inserted through circular portion 40a and slid down into slot portion 40b, and respective nuts 42 tighten down on threaded shank 36c against mounting plate 30.

[0027] Referring to FIGS. 1-3 and 5A-5C, mounting plate 30 has an outer surface 31 that faces away from column 12 and from which tread portion 15 extends and an inner surface 32, opposite outer surface 31, which defines a portion of a cylindrical surface with its curvature about a vertical axis, as oriented in FIG. 1. Before attachment to column 12 and in an unstressed state (as shown in FIG. 5B), inner surface 32 of mounting plate 30 has a radius r2 that is less than the radius r1 of the outer surface of column 12. In some embodiments, unstressed radius r2 is about 1/16 to 3/16 less than r1. In this way, when mounting plate 30 is tightened down against column 12, plate 30 elastically deforms to conform to the shape of the column's outer surface (as shown in FIG. 5C), thereby increasing the radius of curvature of inner surface 32 so that inner surface 32 substantially abuts column 12. In a preferred embodiment, mounting plate 30 may be formed of A36 hot rolled steel. Because the mounting plate's deformation is elastic, mounting plate 30 remains in tension, thereby maintaining a force that biases against the tension of the carriage bolt. This tension on the carriage bolts causes a normal force between the threads of the carriage bolts and the threads of the respective nuts 42, thereby providing a friction force between the respective components that inhibits the nut from unscrewing from the carriage bolt.

[0028] It can thus be seen that the present invention provides a novel tread mounting system for a spiral staircase. While one or more preferred embodiments of the invention have been described above, it should be understood that any and all realizations of the present invention are included within the scope and spirit thereof. The embodiments depicted are presented by way of example only and are not intended as limitations upon the present invention. Thus, it should be understood by those of ordinary skill in this art that the present invention is not limited to these embodiments since modifications can be made. Therefore, it is contemplated that any and all such embodiments are included in the present invention as may fall within the scope and spirit thereof.