THEREOF

Technical Field The present invention relates essentially to the construction industry and particularly the production of cantilevered stairs. For the production of presently known cantilevered stairs, wooden treads, metal frames and reinforced concrete treads are used.

Background Art The assembling of the cantilevered wood tread is very complicated and requires workmanship of the highest standards. With high labour expenditure, deep holes are cut in the wall and prefabricated wood treads are fitted into the wall; it is very complicated task to secure the wood treads in the wall because the holes were cut with some clearance, which should be filled with concrete mix or other material. When the concrete is used for filling, it is necessary to insulate the cantilevered wood tread in order to avoid impact of moisture; therefore, this method requires additional labour costs and consumption of materials. The assembling of the wooden treads results in high labour costs; errors of assembling are inevitable; moreover, if the wall is finished, the assembling of treads by this method completely damages the finish of the wall, and additional labour and material costs are incurred. (SU771292, 11.12.1978).

When metal members are used for production of cantilevered treads, a frame is built out of metal members, and the method of assembling of metal members is inevitably more complicated as compared to wood treads because, for securing, there is no plane that could act as a cantilever in the wall. The method of assembling is the same as in the case of wood treads: deep holes are cut in the wall and metal frames are mounted to the wall; it results in high labour costs and is related to inevitable errors of assembling. After assembling, the metal frame is finished with natural wood, decorative panels, floorboards or other materials. Finally, the cantilevered tread has a relatively large cross-section because the structure contains the metal frame, as a load-bearing member, and the finish made individually. During the exploitation, the structure is not stable and reliable enough because of a rather thin layer of finish materials. (SU1765327, 12.11.1990). When reinforced concrete treads are used, the assembling method is inevitably the same.

With high labour expenditure, deep holes are cut in the wall and prefabricated reinforced concrete treads are mounted to the wall. After assembling, the reinforced concrete tread is finished with natural wood, decorative panels, floorboards or other materials. As in the case of metal frame, the reinforced concrete tread has a relatively large cross-section because the structure consists of the metal frame, as a load-bearing member, and the finish made individually; moreover, impact resistance of the cantilevered reinforced concrete tread is rather low. The live load capacity is not high because of a thin layer of finish materials. (SU1765327, 12.11.1990).

The main disadvantages of presently known cantilevered treads are as follows: very high labour costs, inevitable assembling errors, and inevitably large cross-section of the tread; furthermore, such treads may be installed on a wall that is thick enough and made of strong materials. The disadvantage of cantilevered wood treads is related to a complicated mounting in the wall; moreover, in order to avoid additional labour costs and material consumption, the assembling should be completed before the finishing of the wall. But practically it is impossible to avoid external physical damage to the surface of treads, which may be irreparable if cantilevered wood treads were assembled during this stage of construction. The main disadvantage of the cantilevered wood tread, however, is a low fire resistance, and even lower flame resistance. The main disadvantage of the cantilevered reinforced concrete tread is a complicated mounting in the wall, low impact resistance, low live load capacity, when of smaller cross-section, and relatively large cross-section of the finished tread. The main disadvantage of production of the metal frame for cantilevered treads is a complicated securing in the wall, and very large cross-section of the finished tread; moreover, thin finish of the metal frame is structurally weak and unreliable during the exploitation.

Summary of Invention

The purpose of the present invention is to provide a method for the production of a cantilevered stair and particularly the production of a cantilevered tread. Low labour costs of production and assembling. Shorter process of production and assembling. Reduction of the cross-section and self-weight of the cantilevered tread. Increase the load carrying capacity of the cantilevered tread without increasing its cross-section and self- weight. Application and installation of cantilevered treads in walls of any construction. Maximum exploitation durability of the cantilevered tread, and protection of the structure against fire.

The main characteristic of the present invention is that the cantilevered tread includes load- carrying metal strips.

The method of production of the cantilevered tread: grooves are milled into a wood member, load-carrying metal strips are fitted into the grooves, and the wood members are glued together.

For the production of the cantilevered tread, various materials are used. A member for fixing the tread to the wall, made of a metal sheet, is welded to metal strips carrying the tread, wood members are assembled and glued to the load-carrying metal strips, and the structure is secured with bolts transverse with respect to the structure.

Brief Description of Drawings

A better understanding of the invention will result from the following description of the cantilevered tread with reference to the following drawings:

Fig. 1 (a-e). The cantilevered tread comprises load-carrying metal strips (metal fixing member), bolts transverse with respect to the structure, and wooden members:

a) - Perspective view; b) - Detailed structure; c) - Top view; d) - Side view; e) - Sectional view A

Fig. 2a. Fragment of the cantilevered stair

Description of the Preferred Embodiments Figure 1 (a-e) shows the cantilevered tread which contains a metal fixing member, geometric characteristics and class of which should be selected considering the self- weight of the tread. Metal strips (1) bearing the tread, geometric characteristics and class of which should be selected considering the length and cross-section (e) of the tread. The bolts transverse with respect to the structure (3), the cross-section of which should be selected considering the width and cross-section (e) of the tread; wooden members (2), the cross-section and length of which should be selected considering the width and cross- section (e) of the tread.

The structure of cantilevered tread (b) is characterised in that the mounting to the wall is very simple (Fig. 2a). According to the invention, the metal member (4) is welded to the load-carrying metal strips (1) of the tread (a). After producing the cantilevered tread (a) and welding the fixing member (4), the cantilevered tread is pressed against the wall at the required position and fixed with standard anchor bolts, the number depends on the length and weight of the tread. Where a wall structure is weak and unreliable, the fixing member (4) of the cantilevered tread (Fig. 2a) is mounted with through bolts, which are fixed with nuts and washers of an appropriate dimension on the other side of the wall. On the front side of the cantilevered tread (a), bolts are welded to the fixing member (4) in order to reduce the depth of insertion into the wall. The method for production of the cantilevered tread (a) is simple: prior to gluing, grooves are milled into the wooden members (2) for placing the load-carrying metal strips (1). After fitting load-carrying metal strips (1) between the wooden members (2), wood items are glued together applying a wood glue. For additional strength and longevity of the cantilevered tread (a), the cantilevered tread (a) is secured with bolts (3) transverse with respect to the structure, diameter and length of which should be selected considering the length of the structure. Reinforcement of wood members (2) with load- carrying metal strips (1) ensures a sufficiently stable and high load-carrying capacity without the need of increasing the cross-section and self-weight of the structure. This is the key object of the present invention (reliable and relatively low cost mounting to the wall, sufficiently reliable structure of small cross-section). Simple method for mounting to the wall, the structure (b) is sufficiently long, of small cross-section (e) and sufficiently resistant to various factors: this is the solution of the main disadvantage of the cantilevered tread (a). The inventive tread (b) has a higher impact resistance and live load capacity as compared to the cantilevered reinforced concrete tread. The impact resistance is declared by the load capacity and not by external damage. Being fabricated of wood, the cantilevered tread (a) has a standard external resistance and no additional protection is applied. Being reinforced with load-carrying metal strips (1), the treads of novel construction has a sufficient fire resistance because, in the event of fire, the spread of flames would be slowed by the load-carrying metal strips (1) and transverse bolts (3). Should the wooden members (2) burn down, it will be possible to climb the remaining, even deformed, structure consisting of the load- carrying metal strips (1) and transverse bolts (3). It is possible, however, to enhance significantly the fire resistance by selecting appropriate parameters in terms of thickness and class of a metal sheet for and geometrical structure of load-carrying slips (1) without impairing the aesthetic value of tread (a) and increasing the cross- section of the cantilevered tread (e); for additional fire safety, the cantilevered tread (a) may be covered by a coating of fire-retardant varnish or paint, if necessary.