EP1122379A2

EP1122379A2 - Curved staircase and stair tread for curved staircase

Info

Publication number: EP1122379A2
Application number: EP01301080A
Authority: EP
Inventors: Tetsuya c/o Sweden House Co. Ltd. Matsuoka; Yutaka c/o Sweden House Co. Ltd. Kuroda
Original assignee: Sweden House Co Ltd
Current assignee: Sweden House Co Ltd
Priority date: 2000-02-07
Filing date: 2001-02-07
Publication date: 2001-08-08
Anticipated expiration: 2021-02-07
Also published as: NO20010630D0; NO319433B1; NO20010630L; EP1122379B1; JP3294836B2; JP2001220874A; DK1122379T3; EP1122379A3

Abstract

A curved staircase (1) and a stair tread (4,5,6,7) for a curved staircase (1) capable of reducing a stock space used for stock keeping, enhancing the working efficiency for shipment without requiring a selection operation in accordance with a curve direction of a curved staircase (1), and facilitating assembly at a building site is provided.

A curved staircase A (1) is formed by asymmetrical stair treads (4,5,6 and 7) such that finishing process for enabling use as a treadboard is applied to one horizontal surface of each stair tread (4,5,6,7), which can be an upper surface when arranged in a curved portion (10) bent in the right-hand direction and the same finishing process as that for the former horizontal surface is applied to the other horizontal surface of the stair tread (4,5,6,7), which can be an upper surface when the stair tread (4,5,6,7) is inverted to be arranged in the curved portion (10) bent in the left-hand direction.

Description

The present invention relates to a curved staircase which is provided to an architectural structure such as a timbered house and includes a linear or straight portion by which a resident and the like moves up and down in a straight line and a curved portion by which he/she moves up and down while rounding a turn, and to a stair tread provided in the curved portion of the curved staircase.
A staircase of a timbered house is composed of a plurality of stair treads and stringers which support from both sides each stair tread arranged at a predetermined position. Conventionally, an operator performs a planing or grooving process on each stair tread and on the stringers in accordance with a house under construction.
Even a skilled operator requires a relatively long time to perform the processing operation with respect to each stair tread or to the stringers at a building site, which may inconveniently reduce working efficiency.
Therefore, a so-called precut staircase is known which needs only assembling of each stair tread with the stringers to be carried out at a building site. According to the precut staircase, the stair treads and the stringers which have been precut in a factory are combined in accordance with a configuration of the staircase and shipped to a building site. When assembling the staircase at the building site, the treads to which the stair tread finishing work has been applied are turned upwards and assembled between stringers. Consequently, as compared with the situation where the operator processes each stair tread and the stringers at the building site, the work period can be shortened without depending on a skill level of the operator, and wastage of materials as a result of process error can be eliminated.
As staircases for timbered houses, there are available straight staircases which enable upward and downward movement in a straight run and curved staircases for upward and downward movement with a turn somewhere in the middle. Further, as curved staircases, there are a right-hand curved staircase enabling upward movement while turning (or circling) in the right-hand direction and a left-hand curved staircase enabling upward movement while turning (or circling) in the left-hand direction.
The linear staircase is formed by arranging a plurality of stair treads in a straight line. On the other hand, the curved staircase is formed by combining a linear portion in which the stair treads are arranged in a line and a curved portion in which the stair treads are arranged around a curve.
The respective stair treads arranged in the linear staircase and in the linear portion of the curved staircase are symmetrical and have the same shape. On the other hand, each stair tread arranged in the curved portion of the curved staircase is asymmetrically formed. An example of an asymmetrical stair tread, is where the stair tread is formed as a substantially triangular shape as seen in plan, in which the width dimension of an outer side edge portion positioned on the outer peripheral side of the curve direction is larger than that of the inner side edge portion positioned on the inner peripheral side of the curve.
Despite the fact that each stair tread used for the curved portion in the right-hand curved staircase and that in the left-hand curved staircase have the same shape, treadboard finishing work is applied to opposed sides of these stair treads. That is, each stair tread in the curved portion of the right-hand curved staircase is arranged so that the side edge having the wider width dimension is positioned on the left side as seen from the upper direction, and the tread finishing work such as lacquer coating is applied only to the upper surface of each stair tread. On the contrary, with the curved portion of the left-hand curved staircase, each stair tread is arranged so that the side edge having the wider width dimension is positioned on the right side as seen from the upper direction and the tread finishing work such as lacquer finish is applied only to the upper surface of each stair tread.
As described above, a stair tread used in the curved portion of the right-hand curved staircase is different from a stair tread used in the curved portion of the left-hand curved staircase. Therefore, with a precut staircase, each stair tread for a right-hand curved staircase and each stair tread for a left-hand curved staircase are kept in stock, and any staircase is selected in accordance with the design of a house to be constructed so that the necessary stair treads are delivered to a building site.
In the case of a precut staircase, however, multiple kinds of inventories are necessary depending on the number of steps of a staircase or absence/presence of a landing.
Moreover, different stock is necessary in accordance with each type of staircase, i.e., for the right-hand staircase and the left-hand staircase, as well as stock for linear staircases and accordingly a large stock space is inconveniently required.
Additionally, in the case of assembling the respective right- and left-hand sets in the precut staircase, an error in selection may occur such that the wrong stair tread for use in the curved portion is chosen for the right-hand curved staircase and the left-hand curved staircase.
When shipping a precut staircase, a choice between a right-hand curve and a left-hand curve is required as well as a selection in accordance with the number of steps or presence/absence of a landing of the staircase. This may lead to complicated selection work. Therefore, the working efficiency for shipment can be reduced, thereby resulting in delay of shipment.
In order to avoid the above-described problems, the present invention provides a curved staircase and a stair tread for the curved staircase capable of reducing the stock space required for stock keeping, enhancing the working efficiency for shipment by avoiding the need for selection of different treads depending on the curve direction of the curved staircase required, and facilitating assembly in a building site.
According to the present invention there is provided a curved staircase comprising a linear portion in which a stair tread having a symmetrical shape is arranged and a curved portion in which a stair tread having an asymmetrical shape is arranged, wherein a finishing process is applied to one horizontal surface of each asymmetrical stair tread, which surface is an upper surface when arranged in the curved portion bent in the right-hand direction, so that the horizontal surface can be used as a treadboard, and substantially the same finishing process as that for one horizontal surface is applied to the other horizontal surface which surface is an upper surface when arranged in the curved portion bent in the left-hand direction by inverting the stair tread.
With the curved staircase of the present invention, asymmetrical stair treads having substantially the same finishing process applied to both horizontal surfaces are arranged in the curved portion. As a result, a right-hand curved staircase can be formed by arranging one horizontal surface of each stair tread as a treadboard in the curved portion. Further, when each stair tread is inverted and the other horizontal surface is arranged in the curved portion as the treadboard, the left hand curved staircase can be formed. It is to be noted that the stair treads arranged in the linear portion have asymmetrical shape and the linear portion can be hence formed in both the right- and left-hand curved staircases without inverting the stair treads.
Thus, according to the curved staircase of the present invention, the same type of stair treads can be used for both a right-hand curved staircase and for a left-hand curved staircase. Therefore, in cases where the staircase is precut to be kept in a factory for example, different stair treads adapted specifically for a right-hand curved staircase or for a left-hand curved staircase do not have to be kept, thereby reducing the stock space. Moreover, in the case of shipment to a building site, since a troublesome choice of the stair treads depending on the right-hand curved staircase and the left-hand curved staircase is no longer necessary, the operation for shipment can be reduced to enable rapid shipment.
Further, in the present invention, the asymmetrical stair tread may include grooves, preferably concave grooves, having substantially the same shape on both horizontal surfaces along its nosing, the groove on one horizontal surface being used as an attachment groove for an antiskid member and the groove on the other horizontal surface being used as a connection groove for a riser. When forming either a right-hand curved staircase or a left-hand curved staircase, the antiskid member is attached to the groove on the upper side of the stair tread, which can be obtained after inverting the stair tread, if necessary, and the riser is connected to the concave groove on the lower surface. By doing so, finishing work for the concave groove at the building site is no longer necessary, and staircase assembly is facilitated, thereby shortening the work period.
Furthermore, the present invention also provides a curved staircase comprising a linear portion in which a symmetrical stair tread is arranged and a curved portion in which an asymmetrical stair tread is arranged, wherein stringers, which are provided on at least both sides of each stair tread constituting the curved portion to support the side edge portions of each stair tread, have an assembling concave portion supporting one side edge portion of each stair tread arranged in the curved portion, being formed on one vertical surface when the curved portion is bent in the right-hand direction, and have the assembling concave portion supporting the other side edge portion of each stair tread arranged in the curved portion, being formed on the other vertical surface when the curved portion is bent in the left-hand direction.
According to the curved staircase of the present invention, stringers having concave portions formed on both its vertical surfaces are provided. Consequently, the right-hand curved staircase can be formed by supporting each stair tread on one vertical surface of the stringers, and the left-hand curved staircase can be formed by supporting each stair tread on the other vertical surface of the stringers.
Therefore, according to the curved staircase of the present invention, the same type of stringers can be used for both the right-hand curved staircase and the left-hand curved staircase. Thus, in case of precutting the staircase in the factory to be kept for example, store keeping of different stringers adapted specifically for a right-hand curved staircase or for a left-hand curved staircase is no longer necessary, thereby reducing the stock space. Further, in the case of shipment to a building site, a choice of the stringers according to the right-hand curve and the left-hand curve is not required, and the work for shipment can be hence reduced to enable rapid shipment.
Moreover, the asymmetrical stair treads arranged in the curved portion of the curved staircase, substantially the same finishing process is applied to the stair treads so that the both upper and lower horizontal surfaces can be used as treadboards, a right-hand curved portion being formed when one horizontal surface is positioned on the upper side as the treadboard and a left-hand curved portion being formed when the other horizontal surface is positioned on the upper side as the tread by inverting the stair tread.
According to the stair tread of the present invention, since the same finishing process is applied to both the upper and lower horizontal surfaces so that they can be used as treads, a desired curved portion can be readily formed by selecting one of these horizontal surfaces as the treadboard, depending on whether a right or left curved direction is required.
That is, a right-hand curved staircase can be formed by arranging the stair tread in the curved portion with one horizontal surface as a treadboard, and a left-hand curved staircase can be formed by inverting the stair tread to be arranged in the curved portion with the other horizontal surface as a treadboard. In this manner, the same type of stair treads can be used for both a right-hand curved staircase and a left-hand curved staircase. Therefore, when the staircase is precut in a factory to be kept for example, store keeping of different stair treads adapted specifically for a right-hand curved staircase or a left-hand curved staircase is no longer necessary, thereby reducing stock space. Further, in the case of shipment to a building site, since a choice of the stair tread in accordance with the right-hand curve and the left-hand curve is not necessary, the operation for shipment can be reduced to enable rapid shipment.
Additionally, when precutting the stair tread in a factory, applying the same process to both horizontal surfaces can suffice, thereby improving the working efficiency at the time of precutting.
Moreover, the stair tread may be provided with concave grooves having substantially the same shape on the both horizontal surfaces along its nosing, the concave groove on one horizontal surface of the treadboard being used as an attachment groove for an antiskid member and the concave groove on the other horizontal surface being used as a connection groove for a riser.
By providing the concave grooves to the stair tread, when one horizontal surface is used as a tread, an antiskid member can be attached to the concave groove on the tread side and a riser can be attached to the concave groove on the other horizontal surface. As described above, since the concave grooves having the same shape can be provided on both horizontal surfaces, the working efficiency can be improved in case of precutting the stair tread in a factory and the like. Further, the processing operation for the concave grooves is no longer necessary at a building site, and assembly of the staircase is facilitated, thereby shortening the work period.
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-
Fig. 1 (a) is a diagrammatical plan view showing a right-hand curved staircase in a curved staircase according to an embodiment;
Fig. 1 (b) is a diagrammatical plan view showing a left-hand curved staircase in the curved staircase according to the embodiment;
Fig. 2(a) is a partial diagrammatical perspective view showing a curved portion in Fig. 1(a);
Fig. 2(b) is a partial diagrammatical perspective view showing a curved portion in Fig. 1 (b) ;
Fig. 3(a) is a diagrammatical side elevation of a fourth stringer adopted in the curved staircase according to the embodiment;
Fig. 3(b) is a diagrammatical side elevation of a fifth stringer adopted in the curved staircase according to the embodiment;
Fig. 3(c) is a diagrammatical side elevation of a third stringer adopted in the curved staircase according to the embodiment;
Fig. 3(d) is a diagrammatical side elevation of a turning post adopted in the curved staircase according to the embodiment;
Fig. 3(e) is a diagrammatical side elevation of a first stringer adopted in the curved staircase according to the embodiment;
Fig. 3(f) is a diagrammatical side elevation of a second stringer adopted in the curved staircase according to the embodiment;
Fig. 4(a) is a diagrammatical plan view showing a right-hand curved staircase in the curved staircase according to another embodiment;
Fig. 4(b) is a diagrammatical plan view showing a left-hand curved staircase in the curved staircase according to the embodiment;
Fig. 5(a) is a diagrammatical side elevation of a second stringer adopted in the curved staircase according to the embodiment;
Fig. 5(b) is a diagrammatical side elevation of a third stringer adopted in the curved staircase according to the embodiment;
Fig. 5(c) is a diagrammatical side elevation of a first stringer adopted in the curved staircase according to the embodiment;
Fig. 5(d) is a diagrammatical side elevation of a turning post adopted in the curved staircase according to the embodiment;
Fig. 6(a) is a diagrammatical perspective view showing a case where one horizontal surface of a stair tread is used as a treadboard; and
Fig. 6(b) is a diagrammatical perspective view showing a case where the Fig. 6(a) stair tread is inverted to use the other horizontal surface as a treadboard.
An embodiment of the present invention will now be described below with reference to Figs. 1 (a) through 6 (b).
A staircase A according to this embodiment is provided in a non-illustrated timbered house, and this is a so-called a precut staircase such that respective elements are precut in a factory and assembled at a building site. According to the curved staircase A of this embodiment, it is possible to selectively form a right-hand curved staircase 1 by which a user moves up while turning 180° in the right-hand direction as shown in Fig. 1 (a) and a left-hand curved staircase 2 by which a user moves up while turning 180° in the left-hand direction as shown in Fig. 1(b).
As shown in Fig. 1(a), the right-hand curved staircase 1 is provided with a plurality of symmetrical (rectangular as seen in plan) stair treads 3 (although eight stair treads are provided in this embodiment, all the stair treads have the same shape, and the same reference numeral is hence given to these stair treads) and four asymmetrical stair treads 4, 5, 6 and 7. A predetermined number of the symmetrical stair treads 3 are arranged in a first linear portion 8 on a lower side and a second linear portion 9 on an upper side (four stair treads for each linear portion), and the asymmetrical stair treads 4, 5, 6 and 7 are arranged in a curved portion 10 by which a user goes up while rounding a turn. A landing 11 is provided between the first linear portion 8 and the curved portion 10, and the second linear portion 9 follows the curved portion 10. Each of the asymmetrical stair treads 4, 5, 6 and 7 is formed into a substantially triangular shape in plan such that the width dimension on the outer peripheral side is larger than that on the inner peripheral side in the curve direction.
Further, both side edge portions of each stair tread 3 in the first linear portion 8 are supported by a first stringer 12 and a second stringer 13. The respective stair treads 3, 5, 6 and 7 in the curved portion 10 and the second linear portion 9 are supported by a third stringer 14 and a fourth stringer 15 at side edge portions on the outer peripheral side in the curve direction and supported by a turning post 16 and a fifth stringer 17 at the side edge portions on the inner peripheral side in the curve direction.
It is to be noted that the landing 11 is supported by a non-illustrated support and a base board 18 is provided on the outer peripheral side of the landing 11. Further, although not shown, the respective stringers 12, 14 and 15 are integrally fixed to an interior wall of a stair well and the stringers 13 and 17 and the turning post 16 are integrally fixed to a partition wall of the stair well.
The left-hand curved staircase 2 shown in Fig. 1(b) is different from the right-hand curved stair 1 shown in Fig. 1 (a) only in the curve direction of the curved portion 10 and uses the stair treads 3, 4, 5, 6 and 7, the stringers 12, 13, 14, 15 and 17 and the turning post 16 similar to those of the right-hand curved stair 1.
That is, the same finishing process is applied to the horizontal surfaces on both the upper and lower sides of the asymmetrical stair treads 4, 5, 6 and 7 as shown in Figs. 2(a) and 2(b). As to the finishing process, for example, lacquer coating is applied so that both the upper and lower horizontal surfaces can be used as the treadboard. When one horizontal surface of each of the stair treads 4, 5, 6 and 7 is turned upwards and are arranged as shown, the curved portion 10 which is bent in the right-hand direction is formed as shown in Fig. 2(a). Further, when the respective stair treads 4, 5, 6 and 7 are inverted and arranged so that the other horizontal surface is turned upwards, the curved portion 10 which is bent in the left-hand direction is formed as shown in Fig. 2(b).
It is to be noted that since the symmetrical stair tread 3 can be used without being inverted for both the right hand curved staircase 1 and the left-hand curved staircase 2 as shown in Fig. 1 (a) and Fig. 1 (b), the finishing process for obtaining the treadboard may be applied only to one horizontal surface. Further, a riser 19 is provided between the respective stair treads 3, 4, 5, 6 and 7 as partially shown in Figs. 2 (a) and 2 (b).
As shown in Fig. 3(a), the fourth stringer 15 includes a stair tread supporting concave portion 20 which engages with and supports one side edge portion of each of the stair treads 5, 6, 7 and 3 (see Fig. 1) from the curved portion 10 to the second linear portion 9, and a riser supporting concave portion 21 which engages with and supports one side edge portion of the riser 19 (see Fig. 2) provided between the respective stair treads 5, 6, 7 and 3. As shown in Fig. 3(b), the fifth stringer 17 includes a stair tread supporting concave portion 20 which engages with and supports a part of the other side edge portion of each of the stair treads 6, 7 and 3 and the other side edge portion of the stair tread 5 from the curved portion 10 to the second linear portion 9 so as to be opposed to the fourth stringer 15, and a riser supporting concave portion 21 which engages with and supports the other side edge portion of the riser 19 provided between the respective stair treads 5, 6, 7 and 3. As shown in Fig. 3(c), the third stringer 14 includes a stair tread supporting concave portion 20 which engages with and supports one side edge portion of each of some stair treads 4 and 5 in the curved portion 10, and a riser supporting concave portion 21 which engages with and supports one side edge portion of the riser 19 provided between the respective stair treads 4 and 5. As shown in Fig. 3(d), the turning post 16 includes a stair tread supporting concave portion 20 which engages with and supports the other side edge portion of each of the stair treads 4 and 5 in the curved portion 10 so as to be opposed to the third stringer 14, and a riser supporting concave portion 21 which engages with and supports the other side edge portion of the riser 19 provided between the respective stair treads 4 and 5.
The respective stringers 15, 17 and 14 and the turning post 16 shown in Figs. 3(a) to 3(d) also include the stair tread supporting concave portions and the riser supporting concave portions having the same shape on the other vertical surface (a non-illustrated back side in the drawing) on the opposite side of the illustrated vertical surface at the same positions as those of the stair tread supporting concave portions 20 and the riser supporting concave portions 21. When forming the right-hand curved staircase 1 shown in Fig. 1(a), the respective stair treads 4, 5, 6, 7 and 3 are supported by the stair tread supporting concave portions 20 and the riser supporting concave portions 21 of the respective stringers 15, 17 and 14 and the turning post 16 shown in Figs. 3(a) to 3(d) on the illustrated one vertical surface. When forming the left-hand curved stair case 2 shown in Fig. 1(b), the respective stair treads 4, 5, 6, 7 and 3 are supported by the stair tread supporting concave portions and the riser supporting concave portions of the respective stringers 15, 17 and 14 and the turning post 16 shown in Figs. 3 (a) to 3 (d).
Further, as shown in Fig. 3 (e), the first stringer 12 includes a stair tread supporting concave portion 20 which engages with and supports one side edge portion of each stair tread 3 in the first linear portion 8, and a riser supporting concave portion 21 which engages with and supports one side edge portion of the riser 19 provided between the respective stair treads 3. Similarly, the second stringer 13 is so provided as to be opposed to the first stringer 12 and, as shown in Fig. 3(f), includes a stair tread supporting concave portion 20 which engages with and supports the other side edge portion of each stair tread 3 in the first linear portion 8 and a riser supporting concave portion 21 which engages with and supports the other side edge portion of the riser 19 provided between the respective stair tread 3. Since each stair tread 3 provided in the first linear portion 8 is symmetrical, the first stringer 12 and the second stringer 13 can be commonly used in both the right-hand curved staircase 1 shown in Fig. 1(a) and the left-hand curved staircase 2 shown in Fig. 1(b) if the stair tread supporting concave portions 20 and the riser supporting concave portions 21 are previously formed only on the illustrated one vertical surface.
As described above, in the curved staircase A according to this embodiment, since the same finishing process is applied to both horizontal surfaces of the stair treads 4, 5, 6 and 7 arranged in the curved portion 10, both the right- and left-hand curved portions 10 can be easily formed by only inverting the stair treads in accordance with the curve direction even though the respective stair treads 4, 5, 6 and 7 are asymmetrical, as shown in Figs. 2(a) and 2(b). Moreover, since the stair tread supporting concave portions 20 and the riser supporting concave portions 21 having the same shapes are provided on the respective stringers 15, 17 and 14 and the turning post 16 shown in Figs. 3(a) to 3(d) at the same position on the both vertical surfaces, both the right-hand curved staircase 1 depicted in Fig. 1(a) and the left-hand curved staircase 2 illustrated in Fig. 1(b) can be readily formed. The right-hand curved staircase 1 and the left-hand curved 20 staircase 2 are commonly used, and separate store keeping of the right-hand curved staircase 1 and the left-hand curved staircase 2 is hence no longer necessary in case of precutting the staircase in, e.g., a factory for storage, thereby reducing the stock space.
Another embodiment will now be described. According to a curved staircase B of another embodiment, it is possible to selectively form a right-hand curved staircase 22 by which a user goes up while turning 90° in the right-hand direction as shown in Fig. 4(a) and a left-hand curved staircase 23 by which a user goes up while turning 90° in the left-hand direction as shown in Fig. 4 (b).
As shown in Fig. 4(a), the right-hand curved staircase 22 includes a plurality of symmetrical (rectangular as seen in plan) stair treads 3 (each having the same shape) and four asymmetrical stair treads 4, 5, 6 and 7. The asymmetrical stair treads 4, 5, 6 and 7 are provided in a curved portion 10 on a lower side, and the symmetrical stair treads 3 are arranged in a linear portion 24 on the upper end continuously from the curved portion 10. A single stair tread 25 for a first step to move up is provided to the lower step of the curved portion 10. Each of the symmetrical stair treads 3 and the asymmetrical stair treads 4, 5, 6 and 7 are similar to those in the foregoing embodiment. That is, the same finishing process is applied to the upper and lower horizontal surfaces of the asymmetrical stair treads 4, 5, 6 and 7, and the finishing process is applied only to one horizontal surface of the symmetrical stair treads 3.
Further, the stair treads 4 and 5 in the curved portion 10 are supported by a first stringer 26 at one side edge portion on the outer peripheral side in the curve direction and supported by a turning post 27 at the other side edge portion on the inner peripheral side in the curve direction. The respective stair treads 5, 6, 7 and 3 in the curved portion 10 and the linear portion 24 are supported by a second stringer 28 at one side edge portion on the outer peripheral side and supported by a third stringer 29 at the other side edge portion on the inner peripheral side.
It is to be noted that the stair tread 25 for a first step to move up is supported by the first stringer 26 at one side edge portion and supported by a turning post 27 at the other side edge portion. In addition, a nonillustrated riser (see the riser 19 in the curved staircase A described in the foregoing embodiment) is provided between the respective stair treads 25, 4, 5, 6, 7 and 3. Moreover, although not shown, the respective stringers 26 and 28 are integrally fixed on an interior wall of a stair hall, and the stringer 29 and the turning post 27 are integrally fixed on a partition wall of the stair hall.
The left-hand curved staircase 23 shown in Fig. 4(b) is different from the right-hand curved staircase 22 shown in Fig. 4(a) in the curve direction but uses the respective stair treads 25, 4, 5, 6, 7 and 3 and the respective stringers 26, 28 and 29 similar to those in the right-hand curved staircase 20 22.
As shown in Fig. 5(a), the second stringer 28 includes a stair tread supporting concave portion 20 which engages with and supports one side edge portion of each of the stair treads 5, 6, 7 and 3 from the curved portion 10 to the linear portion 24, and a riser supporting concave portion 21 which engages with and supports one side edge portion of a riser provided between the respective stair treads 5, 6, 7 and 3. As shown in Fig. 5(b), the third stringer 29 includes a stair tread supporting concave portion 20 which partially engages with and supports the other side edge portion of each of the stair treads 6, 7 and 3 and the other side edge portion of the stair tread 5 from the curved portion 10 to the linear portion 24, so as to be opposed to the second stringer 28, and a riser supporting concave portion 21 which engages with and supports the other side edge portion of the riser provided between the respective stair treads 5, 6, 7 and 3. As shown in Fig. 5(c), the first stringer 26 includes a stair tread supporting portion 20 which engages with and supports one side edge portion of each of some stair treads 4 and 5 in the curved portion 10, and a riser supporting concave portion 21 which engages with and supports one side edge portion of the riser provided between the stair treads 4 and 5. As shown in Fig. 5(d), the turning post 27 includes a stair tread supporting concave portion 20 which engages with and supports the other side edge portion of each of some stair treads 4 and 5 in the curved portion 10 so as to be opposed to the first stringer 26, and a riser supporting concave portion 21 which engages with and supports the other side edge portion of the riser provided between the stair treads 4 and 5.
Each of the stringers 28, 29 and 26 shown in Figs. 5(a) to 5(c) is provided with the stair tread supporting portion and the riser supporting concave portion having the same shapes on both the illustrated one vertical surface and the other vertical surface on the opposite side (the non-illustrated back side in the drawing) at the same positions as those of the stair tread supporting concave portion 20 and the riser supporting concave portion 21. Consequently, in case of forming the right-hand curved staircase shown in Fig. 4(a), the respective stair treads 4, 5, 6, 7 and 3 are supported by the stair tread supporting concave portion 20 and the riser supporting concave portion 21 on the illustrated one vertical surface of each of the stringers 28, 29 and 26 depicted in Figs. 5(a) to 5(c). Further, in case of forming the left-hand curved staircase 23 shown in Fig. 4(b), the respective stair treads 4, 5, 6, 7 and 3 are supported by the stair tread supporting concave portion and the riser supporting concave portion on the other vertical surface of each of the stringers 28, 29 and 26 illustrated in Figs. 5 (a) to 5(c).
A supporting shoulder portion 30 for supporting the stair tread 25 for a first step to move up is provided at the lower side of the turning post 27, and another riser supporting concave portion 31 for supporting a non-illustrated riser is provided at the end of the supporting shoulder portion 30. Although another riser supporting concave portion 31 may be provided on both vertical surface sides of the turning post 27, one side surface of the supporting shoulder portion 30 extends toward the outside of the partition wall of the non-illustrated stair well to be exposed, and it is hence preferable that this riser supporting concave portion 31 is provided on one vertical surface in accordance with the curve direction or formed at a building site. Further, when the same finishing process is previously applied to the both upper and lower horizontal surfaces of the stair tread 25 for a first step to move up, this stair tread 25 can be inverted to be provided in both the right- and left-hand curved staircases 22 and 23.
As mentioned above, in the curved staircase B according to this embodiment, since the same finishing process is applied to one horizontal surface and the other horizontal surface of the stair treads 4, 5, 6 and 7 arranged in the curved portion 10, both the right- and left-hand curved portions 10 can be readily formed by only inverting the stair treads in accordance with the curve direction as shown in Figs. 4(a) and 4(b) even though the respective stair treads 4, 5, 6 and 7 are asymmetrical. Moreover, since the stair tread supporting concave portions 20 and the riser supporting concave portions 21 having the same shapes are provided at the same positions on the both vertical surfaces of the respective stringers 28, 29 and 26 shown in Figs. 5(a) to 5(c), both the right-hand curved staircase 22 illustrated in Fig. 4(a) and the left-hand curved staircase 23 depicted in Fig. 4(b) can be easily formed. Except the turning post 27, the righthand curved staircase 22 and the left-hand staircase 23 are commonly used, and separate store keeping of the right-hand staircase 22 and the left-hand staircase 23 is hence no longer necessary when of precutting these staircases in, e.g., a factory for storage, thereby reducing the stock space.
It is to be noted that the stair treads having both flat horizontal surfaces to which the finishing process is applied have been described in each of the above embodiments. In such a case, although not shown, the concave groove for attaching the riser 19 is machined along the nosing of the horizontal surface which can be a lower side when arranged in the curved portion 10 at a building site. Moreover, although not shown, a relatively shallow antiskid concave groove may be formed on the both horizontal surfaces of the asymmetrical stair treads 4, 5, 6 and 7 along the nosing at the time of precutting in a factory. In this case, the concave groove for attaching the riser 19 is also machined along the nosing of the horizontal surface which can be a lower side when arranged in the concave portion 10 at a building site.
Additionally, as illustrating only the stair tread 4 in Figs. 6(a) and 6(b), the concave grooves 33 and 34 having the same shape may be provided on each of the asymmetrical stair treads 4, 5, 6 and 7 at the same position along the nosing 32 on the both horizontal surfaces. It is to be noted that Fig. 6(a) shows the case where one horizontal surface of the stair tread 4 serves as a treadboard and Fig. 6(b) shows the case where the stair tread 4 in Fig. 6(a) is inverted so that the other horizontal surface functions as a treadboard. At the time of precutting in a factory, the concave grooves 33 and 34 are formed into such a shape that an antiskid member 35 (made of, e.g., rubber) and the riser 19 can be attached thereto. As shown in Fig. 6(a), when one horizontal surface of the stair tread 4 is used as a treadboard, the antiskid member 35 is attached to the upper concave groove 33 which is exposed as a treadboard, and the riser 19 is attached to the lower concave groove 34. On the contrary, when the stair tread 4 is inverted to use the other horizontal surface as a treadboard as shown in Fig. 6(b), the antiskid member 35 is attached to the upper concave groove 34, and the riser 19 is attached to the lower concave groove 33. By doing so, both concave grooves 33 and 34 can be accurately provided at the time of precutting in a factory, and the labor for machining the both concave grooves 33 and 34 at a building site can be eliminated. Therefore, not only the operation for assembling the curved staircases A and B can be facilitated but also the work period can be shortened.

Claims

A curved staircase comprising a linear portion in which at least one symmetrical stair tread is arranged and a curved portion in which at least one asymmetrical stair tread is arranged,
characterised in that the finishing process for enabling use of each stair tread as a treadboard is applied to a first horizontal surface of said asymmetrical stair tread, which surface is an upper surface when arranged in said curved portion bent in the right-hand direction, and the same finishing process as that for the first horizontal surface is applied to the second horizontal surface, which surface is an upper surface when said stair tread is inverted to be arranged in said curved portion bent in the left-hand direction.
The curved staircase according to claim 1, wherein said asymmetrical stair tread includes grooves having the same shape on both horizontal surfaces along its nosing, said groove on the horizontal surface selected as a treadboard serving as an attachment groove for an antiskid member, said groove on the other horizontal surface serving as a connection groove for a riser.
A curved staircase comprising a linear portion in which at least one symmetrical stair tread is arranged and a curved portion in which at least one asymmetrical stair tread is arranged,
wherein a stringer, which is provided on both sides of each stair tread constituting at least said curved portion and supports a side edge portion of each stair tread, has an assembling concave portion for assembling and supporting one side edge portion of each stair tread arranged in said curved portion being provided on one vertical surface of the stringer, and an assembling concave portion for assembling and supporting the other side edge portion of each stair tread arranged in said curved portion being provided on the other vertical surface of the stringer.
A stair tread for a curved portion of a curved staircase, the stair tread having an asymmetrical shape,
characterised in that the same finishing process for enabling use as a treadboard is applied to both upper and lower horizontal surfaces of said stair tread, a right-hand curved portion being formed when one horizontal surface is turned upwards for use as a treadboard, and a left-hand curved portion being formed when said stair tread is inverted so that the other horizontal surface is turned upwards for use as a treadboard.
The stair tread for a staircase according to claim 4, wherein said stair tread includes grooves having the same shape on both horizontal surfaces along its nosing, said groove on the horizontal surface selected as the treadboard serving as an attachment groove for an antiskid member, said groove on the other horizontal surface serving as a connection groove for a riser.
A stair tread for a curved portion of a curved staircase, the stair tread having an asymmetrical shape and having a first and second horizontal surface, characterised in that both the horizontal surfaces are adapted to function as a treadboard, a curved portion bending to the right being formed when the first surface is uppermost in use and a curved portion bending to the left being formed when the second surface is uppermost in use.
A curved staircase comprising at least one curved portion in which at least one stair tread according to claim 6 is arranged.