In this connection it should be particularly noticed that the term"step", as used in this context, refers not only to a stair, i. e. where the horizontal wall is the tread and the vertical wall is the riser of the step, but also to those cases in which the horizontal wall is a worktop, or a similar surface, and the vertical wall is exposed to view, such as for example in a kitchen. For reasons of greater convenience, use will be made of the term"tread"to indicate the horizontal wall and the term"riser"to indicate the vertical wall of the step throughout the following description.

Steps of the above-mentioned kind have, in the rear portion of the torus, a longitudinal accommodation adapted to receive and hold firmly the front edge of a laminar member of metal or plastics, which extends horizontally and constitutes the resting surface for the tread, in such a manner that it practically cannot slip out after having been installed.

In the European patent no. 0 784 132, such accommodation consists of a groove situated at a distance from the upper edge of the torus, which is equal to or greater than the thickness of the plate or the tiles forming the tread. In the case of heavy loads weighing on the tread, and therefore on the laminar member, the flexural, i. e. bending stress imposed to the portion of the torus lying above the groove may prove excessive. In the case then of a torus made of marble, the milling operation it must undergo in view of working out said groove is quite awkward and demanding owing to both the position in which said groove must be provided and the small cross-sectional size thereof ; it may even prove impossible to carry out if the cross-section of such groove is in a different shape, e. g. is T-shaped. Finally, the actual installation of the laminar member is rather awkward and difficult when carried out with a horizontal (i. e. perpendicular to the torus) movement, owing to the front edge thereof being retained by interference by the same groove. When an adhesive material is used to complete such installation, the same, if not really complex, proves at least quite expensive.

In the Italian utility model filed under the application number TV98U000051 there is described a step in which the front edge of the laminar member is thickened so as to be capable of being retained by the accommodation provided in the torus, said accommodation consisting of a groove, whose cross-section must be given a complementary shape. In this

case, the installation of the laminar member is an easily performed operation, since it is carried out with a sliding movement along the torus, which is in turn provided with a rear resting border strip. On the other hand, the milling operation, which the torus must be subjected to in order to provide the groove, is even in this case quite difficult, if not even impossible, to carry out owing to the cross-sectional shape thereof. In addition, the portion of torus lying above the groove is particularly thin in its cross-section, so that the risk induced by very heavy loads weighing on the tread of the step is even greater than in the previously considered construction.

Similar considerations apply to the steps described in the Italian utility model filed under application number M02000U000015, as well as in the Italian patent application 1 311 823, in which the laminar member is provided with a L-shaped or a T-shaped head portion.

It would therefore be desirable, and it is actually a main purpose of the present invention, to provide steps that are capable of sustaining very heavy loads, and provided with a torus that may be made even of marble and is easy to produce at generally low costs.

According to the present invention, these aims are reached in steps incorporating the features as recited and defined in the appended claims, as this shall be more readily understood from the description that is given below of the preferred, although not sole embodiment illustrated in the accompanying Figure.

While drawing the attention on the fact that this Figure is a cross-sectional view of a step that is illustrated in an intentionally simplified, schematical manner and, therefore, does not reproduce the exact dimensions of the various parts, the Figure itself can be noticed to show following parts of a step: the load-bearing structure 10 of reinforced concrete, the tread 20, the riser 30, the torus 40 and the laminar member 50, the latter forming the resting surface for the tread.

The tread 20 and the riser 30 may for instance be made of either natural or man- made marble plates or tiles. In turn, the torus 40 may itself be of marble, ceramic material or even other materials.

The torus 40 has a front contour that, in a fully conventional manner, includes, when viewed from the top to the bottom, a first bulging, i. e. convex portion 41, a second more or less rectilinear joining portion 42, and a third re-entrant, i. e. concave portion 43. Looking again at it from top downwards, the torus 40 furthermore has a rear contour formed, in succession, by a first vertical portion 44, which directly joins with the above-cited portion 41, a second horizontal portion 45, a third vertical portion 46, and a fourth portion 47, also vertical, from which there starts off the horizontal segment 48 joining the rear contour with the front one under said portion 43.

On the rear side of the torus 40 there are provided two longitudinal grooves 51 and 52 that are substantially rectangular in their cross-section and serve the purpose of accommodating the front portion of the laminar member 50. According to the main feature of the present invention, the first groove 51 is provided between the first portion 44 and the second portion 45 of the rear contour of the torus 40 and, therefore, has a vertical section, whereas the second groove 52 is provided between the third portion 46 and the fourth portion 47 and, therefore, has a horizontal section. These grooves are separated and spaced from each other by the above-mentioned second portion 45 of the rear contour of the torus 40. In the first groove 51 there is accommodated the front edge 55, which is bent to the shape of a"L", of the laminar member 50, whereas the second groove 52 accommodates the terminal (horizontal) edge 56 of a L-shaped appendix 57, which is also a part of the laminar member 50. The other (vertical) side 58 of said appendix 57 lies at a distance from the above-mentioned front edge 55, which is just slightly greater than the distance between said two grooves 51 and 52. In order to enable the above-mentioned portions 55 and 56 of the laminar member 50 to be introduced and accommodated in said grooves smoothly, i. e. without any difficulty, the cross-sectional dimensions of said two grooves 51 and 52, particularly as far as their width is concerned, are so defined as to ensure that there remains an adequate clearance.

The second portion 45 of the rear contour of the torus 40 supports the horizontal section of the laminar member 50, which is comprised between the terminal side 55 and the appendix 57 and, as a result, lies at such a level as to ensure that the tread 20 (with the layer of mortar, not shown, that is required to hold it firmly on the horizontal wall 12 of the load- bearing structure 10) comes to lie flush with the highest point of the torus. The third portion 46 of the rear contour of the torus 40 lies in turn in advance of the fourth portion 47 so as to be able to receive and accommodate the above-mentioned vertical portion 58 of the appendix 57 of the laminar member 50, in front of the vertical wall 11 of the structure 10.

As this clearly emerges from the afore-going description, steps made in accordance with the present invention have following peculiar advantages: a) the torus may be manufactured, i. e. milled in a most expeditious, straightforward manner, without meeting with any particular difficulty, even in the case it is being made of marble, thanks to the fact that the arrangement of the grooves 51 and 52 enables two tools to be used even simultaneously ; moreover, the grooves themselves have a simply shaped cross-section and a relatively large size; b) the laminar member 50 may be manufactured out of an aluminium profile section (which may possibly be drilled and perforated before installation, so as to enable the mortar to more effectively catch hold of, i. e. adhere to the tread 20), which may be processed at

reduced costs and has a good mechanical and environmental strength; c) inserting the parts 55 and 56 in the corresponding grooves 51 and 52 only requires a movement occurring parallel to the torus 40, i. e. orthogonal to the plane of the accompanying Figure, while doing away with the use of any adhesive material whatsoever, so that the installation of the laminar member 50 is most straightforward, easily done and inexpensive; d) the load weighing on the tread 20 does not impart any bending or flexural stress to the portion of the torus that is comprised between the first portions 41 and 44 of the front contour and the rear contour thereof, respectively.

Although the afore-going description and the accompanying Figure refer to the currently preferred embodiment of the present invention, it will be appreciated that the steps may be embodied also in a number of different forms and variants without departing from the scope of the present invention as defined by the appended claims.