Foundation

Abstract

A double raft foundation for buildings includes: a lower raft, a layer of a material with a low friction coefficient applied on the lower raft, a platform having slabs of material with a low friction coefficient, slidingly disposed on the layer, an upper raft joined with the slab platform and a superstructure joined with the upper raft; wherein the upper raft is disposed on the lower raft in such manner that, in case of an earthquake, the platform of slabs of the upper raft can slide slidingly on the layer of the lower raft, allowing the upper raft to move relatively with respect to the lower raft.

Claims

1. A double raft foundation for buildings, the double raft foundation comprising: a lower raft; a layer of material applied to said lower raft; a platform having a plurality of coplanar slabs slidingly disposed on said layer of material on said lower raft; an upper raft joined to said platform; and a superstructure joined to said upper raft, wherein said upper raft is disposed on said lower raft such that said platform can slide on said layer of material on said lower raft so as to allow said upper raft to move relative to said lower raft in an event of an earthquake, a static sliding friction coefficient and a dynamic sliding friction coefficient between said layer of said material on said lower raft and said plurality of coplanar slabs joined to said upper raft are equal to or less than 0.04.

2. The double raft foundation of claim 1, wherein said layer of the material is polytetraflouroethylene and said plurality of coplanar slabs of said platform raft are made of steel or polytetraflouroethylene.

3. The double raft foundation of claim 1, wherein said lower raft is a tank with raised perimeter walls and configured to contain said upper raft.

4. The double raft foundation of claim 3, further comprising: dissipating-dampening devices and centering devices interposed between the perimeter walls of said lower raft and said upper raft to dampen said movement of said upper raft and to center said upper raft with respect to said lower raft after the earthquake.

5. The double raft foundation of claim 1, wherein said layer of material on said lower raft is a layer of polytetraflouroethylene with a thickness of approximately one centimeter to two centimeters.

6. The double raft foundation of claim 1, wherein each slab of said plurality of coplanar slabs of said platform is a rectangular tank with side walls protruding upwardly of said plurality of coplanar slabs from a bottom wall.

7. The double raft foundation of claim 6, wherein each slab has at least one side wall with U-bent upper edges so as to define a housing that receives an upper border of the side wall of an adjacent slab of said plurality of coplanar slabs.

8. The double raft foundation of claim 1, further comprising: an understructure that extends under said lower raft and is joined to said lower raft.

9. The double raft foundation of claim 8, wherein said superstructure joined to said upper raft so as to as to form a prefabricated module separated from a load-bearing structure of a skyscraper, wherein said lower raft is a floor of the skyscraper and the prefabricated module is positioned on the floor of the skyscraper.

Description

(1) Additional characteristics of the invention will become more fully apparent from the following description, which refers to merely exemplary, not limiting embodiments, which are illustrated in the attached technical drawings, wherein:

(2) FIG. 1 is an exploded sectional view of the various parts of the double raft foundation according to the invention;

(3) FIG. 2 is a sectional view of the foundation of FIG. 1 in assembled condition;

(4) FIG. 3 is an exploded perspective view of three slabs of the upper raft of the foundation according to the present invention;

(5) FIG. 4 is partially interrupted sectional view that shows the assembly of two slabs of FIG. 3;

(6) FIG. 5 is a sectional view of a building with a buried understructure and a superelevated structure.

(7) FIG. 6 is a sectional view of a skyscraper wherein each housing module is made with a double raft foundation according to the present invention.

(8) Referring to the figures, the double raft foundation of the invention is disclosed, being generally indicated with reference numeral (1).

(9) With reference to FIGS. 1 and 2, in order to install the double raft foundation (1) according to the present invention, an excavation (20) of the soil (2) is made and lean concrete (21) is cast in the excavation (20), just like in the construction systems that are currently used.

(10) Then, a lower raft (3) of reinforced concrete is made on the lean concrete (21); for instance, in the case of a house with 2-3 floors, the lower raft has a thickness of approximately 30-40 cm. The upper surface (30) of the lower raft (3) is smooth, planar and leveled. Advantageously, a smoothing material, such as cement mortar, is applied on the upper surface (30) of the lower raft to repair the non-uniformities that may be generated when casting the lean concrete (21).

(11) Advantageously, the lower raft (3) can be shaped as a tank with perimeter walls (31) that are raised with respect to the upper surface (30) of the lower raft, in such manner to define a recessed housing (32).

(12) A layer of material with a low friction coefficient, preferably a layer of Teflon (4) with thickness of 1-10 cm, is laid and fixed on the upper surface (30) of the lower raft. The Teflon layer (4) must have a constant thickness and an upper surface (40) that is as uniform as possible. Advantageously, the layer of material with a low friction coefficient may comprise a mix of Teflon and carbon in order to obtain a better sliding and a longer life of the layer of material with a low friction coefficient.

(13) A plurality of slabs (5) forming a platform is disposed on the Teflon layer. The slabs (5) are made of a material with a low friction coefficient, such as steel and/or Teflon.

(14) Advantageously, the slabs (5) are made of steel and have a minimum thickness of 1-2 mm. In this way the steel of the slabs (5) is in direct contact with the Teflon layer (4) and the slabs (5) can slide on the Teflon layer (4). Advantageously, the slabs (5) may be of steel and may have a Teflon-coated lower surface (50). In this way the Teflon surface of the slab (5) comes in contact with the Teflon layer (4), thus minimizing the friction between the Teflon layer (4) and the slab (5). The slab (5) can be made of Teflon only.

(15) Referring to FIGS. 3 and 4, each steel slab (5) is shaped as a rectangular tank provided with a bottom wall (51) and four side walls (52) orthogonally raising from the bottom wall for a height of approximately 2-4 cm.

(16) Two adjacent side walls (52) of a steel slab have a downward U-bent upper edge (53) in such manner to define housing (54) that is open on the bottom. In this way a second slab (5) can be assembled to a first slab (5) that is already laid on the Teflon layer (4), by fitting the upper border of a side wall (52) of the first slab inside the housing (54) of the upper edge of the second slab, in such manner to form a joint between the two slabs and create a single steel surface between the two slabs. In view of the above, the platform is made of a modular structure comprising a plurality of interconnected steel slabs (5).

(17) After assembling the slabs (5), the joints between the slabs are sealed with gaffer tape (not shown in the figures) to prevent the concrete from falling on the Teflon layer (40). Now, having obtained a sealed steel surface, an upper raft (6) is made.

(18) Firstly, steel girders (not shown in the figures) are built on the slabs (5) and then concrete is cast on the slabs (5) in such manner to form the upper raft (6) of reinforced concrete with thickness of approximately 30-40 cm (for houses with 2-3 floors). The upper raft (6) must have surface dimensions (length and width) that are lower than the surface dimensions of the Teflon layer (4) cast on the lower raft (3) in order to make sliding on said Teflon layer (4) possible. For example, the upper raft (6) is centered in the recessed housing (32) of the lower raft (3), leaving a clearance of about 30-50 centimeters between the upper raft and the side walls (31) of the lower raft.

(19) The upper raft (6) is joined to a superstructure (60) that can be provided with one or more housing modules, for instance.

(20) The bottom of the upper raft (6) is the platform composed of the slabs (5) resting on the Teflon layer (4). Considering that the friction of steel on Teflon is similar to the friction on ice, a superstructure (60) that slides on the lower raft (3) with practically no friction is obtained.

(21) The lower raft (3) must be wider than the upper raft (6) to allow for sliding and must have a peripheral raised curb composed of the side walls (31) to prevent the upper raft (6) from coming out of the lower raft (3). Moreover, such a configuration allows for using a dampening system (7) to dampen the sliding of the upper raft (6) and a centering system (8) to center the upper raft (6) with respect to the lower raft (3) when the earthquake is finished. The dampening system (7) and the centering system (8) are interposed between the perimeter walls (71) of the lower raft (3) and the upper raft (6).

(22) Advantageously, the lower raft (3) can be much wider than the upper raft (6). In such a case, the use of dissipating devices and centering devices is not necessary because the upper raft (6) can be centered with respect to the lower raft (3) by means of a jack when the earthquake is finished. This system can be advantageously applied in areas with low seismic hazard in order to reduce costs.

(23) Steel is chosen as friction surface for the upper raft for merely economic reasons. An additional Teflon layer can be used as sliding surface for the upper raft in case of double raft foundations in very cold, very warm, acid and aggressive places, or for special requirements of factories, etc. The sliding between Teflon-Teflon has the same friction as steel-Teflon, both being proximal to the sliding produced between steel and ice.

(24) As an alternative to reinforced concrete, the upper raft (6) and the superstructure (60) joined to the upper raft can be made of another material, such as wood, steel, bricks or stone.

(25) It must be considered that in the double raft foundation (1) the operating thickness is limited to a total of approximately 2 cm, 1 centimeter for the Teflon layer (4) of the lower raft and 1 centimeter for the steel slab (5) of the upper raft.

(26) With reference to FIG. 5, in case of a building with two or three off-ground floors and one underground floor used as garage, the underground floor (understructure (36)) could be typically made with reinforced concrete, thus joining it to the lower raft (3). Instead, the off-ground floors (superstructure (60)) are joined to the upper raft (6). In this way, the seismic shear is made at the height of the ground floor. This will make the building works easier and will reduce the building costs. For example, the understructure (36) and the lower raft (3) are made of reinforced concrete and the superstructure (60) is made of wood.

(27) Always considering the limited thickness that is needed for the operation of the double raft foundation according to the invention, new actions are possible for skyscrapers.

(28) With reference to FIG. 6, the upper raft (6) and the superstructure (60) joined to the upper raft form a prefabricated module (9) separated from the load-bearing structure (S) of the skyscraper. The floors of the skyscraper form the lower rafts (3). A Teflon layer (4) with 1 cm thickness is applied jointly on the lower rafts (3) composed of the skyscraper floors. A platform comprising Teflon slabs (5) with 1 cm thickness is applied jointly under the upper raft (6) composed of the base of the prefabricated module (9). In this way, the prefabricated modules (9) are disposed in the load-bearing structure (S) of the skyscraper with the double raft foundation system.

(29) Dissipating devices (7) and centering devices (8) are interposed between the load-bearing structure (S) of the skyscraper and the upper raft (6) composed of the base of the prefabricated module (9).

(30) In this way the skyscraper will have prefabricated modules (9) that behave differently on each floor, progressively going upwards. The entire load-bearing structure (S) of the skyscraper will be less stressed during the seism. The seismic movement of the load-bearing structure (S) corresponds to a movement of the prefabricated modules that slide on the floors of the load-bearing structure (S).

(31) Numerous variations and modifications can be made to the present embodiments of the invention, within the reach of an expert of the field, while still falling within the scope of the invention.