SUPPORT DEVICE WITH CONTROLLED STIFFNESS

The invention concerns the field of support devices.

More particularly, the invention concerns a support device comprising at least two force transmission parts in mutual contact so as to transmit forces directed substantially in a predefined direction.

In particular by the patent documents referenced FR 1 398 214 A and GB 1 042 397 A, such support devices are well known for equipping various structures or for lowering loads below equipment. They are particularly applied as a structural support device, when a purely static load lowering function is required, and as an isolator when a seismic filtering and/or dampening function is required.

In the example provided in FIG. 1, the part 1 has two convex surfaces 1a, 1b opposite each other, the concavity 20a of a first support plate 2a being placed opposite the first convex surface 1a and the concavity 20b of a second support plate 2b being placed opposite the second convex surface 1b.

Conventionally, a sliding material 3 is interposed in layer form between the part 1 with the convex surfaces and the concavity 20a, 20b of the support plate 2a, 2b for accommodating their relative translational and/or rotational movements. The sliding material defines, via its tribological properties, the coefficient of friction characteristic of the support device 100. The tribological properties of the sliding material 3 are therefore adapted to suit the considered application of the support device. For a structural support device, the sliding material 3 advantageously has a low coefficient of friction to allow for the movements of the structure supported by transmitting the lowest force possible to the bearing structure. Conversely, for an isolator, the sliding material 3 advantageously has a higher coefficient of friction so as to dissipate as much force as possible and thus limit the movement of the supported structure in relation to the bearing structure.

The support plates 2a, 2b fulfil two main functions.

The first function is to allow for the transfer of the forces applied by the part 1 to the convex surfaces, sliding in the concavity 20a, 20b of the support plate 2a, 2b, towards the surrounding structures by distributing them as uniformly as possible. In consequence, the support plates 2a, 2b are dimensioned by the allowable stress of the surrounding structures, whereby this allowable stress depends on the materials constituting these structures and the quality of their contact with the support plates 2a, 2b. Often, shimming is performed by the expulsion or injection of mortar between the support plate 2a and its support so that the contact between the support plate 2a and its support is of satisfactory quality. An equivalent shimming process can take place between the supported structure (bridge, building) and the support plate 2b.

The second function of the support plates 2a, 2b consists in ensuring the correct distribution of the contacts with the part 1 with convex surfaces and the correct distribution of the forces associated with these contacts in order to control the coefficient of friction. The contact forces are closely connected to two parameters, i.e. (i) the geometry of the convex surface 1a, 1b located opposite the concavity 20a, 20b of the support plate 2a, 2b and (ii) the mechanical properties of the sliding material 3.

The influence of the geometry of the convex surface 1a, 1b on the contact forces is connected to the difference between the radius of curvature of the convex surface 1a, 1b and the radius of curvature of the concavity 20a, 20b located opposite. It should be noted that this difference depends on the machining tolerances and mechanical properties of the sliding material 3.

The influence of the mechanical properties of the sliding material 3 on the contact forces is connected to (i) the coefficient of friction of the sliding material 3, in particular dependent on the contact pressure and temperature, and (ii) the compression stiffness of the sliding material 3, dependent on its elasticity module.

In particular, in order to fulfil its two main functions, the support plates are generally huge and therefore very stiff; they are, for example, made from steel and potentially stainless steel. Their design must therefore be compatible with the machining tolerances dependent on the size of the elements of the support device 100.

The support plates 2a, 2b are therefore dimensioned at least in relation to the allowable stress of the surrounding structures and the contact forces generated by the part 1 with convex surfaces.

The contact forces are concentrated at the level of the contact area between the convex surface 1a, 1b and the corresponding concavity 20a, 20b. This area is increasingly narrow as the difference in the radius of curvature between the convex surface and the corresponding concavity increases.

In order to allow for satisfactory dimensions of the support device, many research works have been conducted to draw up and test new materials, and in particular new sliding materials. These materials and the test conditions that must be met are currently subject to standards, such as the European standards EN 1337-7 and EN 15129 for structural support devices and isolators respectively. These standards more particularly provide dimensioning methods for several sliding materials, such as CM1, CM2 and PTFE in the European standard EN 1337-2. The principle proposed by these standards is to limit the radius of curvature of the convex surface 1a, 1b, by using only a few known materials. Tabulated formulae impose the contact surface value and maximum allowable pressure value for each material.

In this context, this invention particularly aims to provide support devices that are satisfactory in terms of the sliding of stresses and dimensioning.

It proposes a support device comprising at least two force transmission parts in mutual contact so as to transmit forces directed substantially in a predefined direction. One of the two parts has a convex surface and the other of the two parts has a concave surface with a larger radius of curvature than said convex surface. One of the convex and concave surfaces is lined with a sliding material. The convex surface is in contact with the concave surface in a contact area. At least one of the two force transmission parts comprises a block of homogeneous material having at least one recess in a portion substantially aligned with the contact area along said direction.

In this design of the support device, an appropriate dimensioning and positioning of the recess(es) in a force transmission part allows the stiffness of this part to be controlled for better sliding the stresses. The dimensioning requirements of the support device and surrounding structure assembly can therefore be relaxed. The dimensioning and positioning of the recess(es) can be determined by the calculation according to the specific mechanical parameters of each structure equipped with a support device according to the invention.

According to one feature, the recess has a shape and dimensions that are chosen according to the stiffness, shape and dimensions of the block of homogeneous material.

Therefore, the precision of the stiffness control of the part is only limited by the accuracy of the recess techniques for this part.

According to an additional feature, the shape and dimensions of the recess are moreover chosen according to the stiffness of the sliding material and the shape and dimensions of the sliding material lining.

According to an additional feature, the block of homogeneous material of the force transmission part has a recess that is centred in relation to a centre line of the convex surface or of the concave surface of the force transmission part.

According to an additional feature, the block of homogeneous material of the force transmission part has several recesses distributed in a symmetrical manner in relation to a centre line of the convex surface or of the concave surface of the force transmission part.

According to an additional feature, the block of homogeneous material of the force transmission part has at least one recess in a face of the force transmission part opposite said convex surface or said concave surface.

According to an additional feature, the force transmission part comprises two parts assembled together by an assembly surface to form the block of homogeneous material and the recess is formed at the level of the assembly surface.

According to an additional feature, at least one recess is filled with a filler material having a stiffness that is less than the stiffness of the homogeneous material of the block. The filler material can be chosen from a group comprising aluminium, bronze and ultra-high performance fibre-reinforced concrete, said group being non-limiting.

Therefore, the local stiffness variation of the force transmission part can still depend on the choice of the filler material, for improved control over this variation and a wider variation range.

One can also consider filling the recess with the filler material so as to make the face of the force transmission part comprising said recess flush. The filler material can restore the shape of the recessed homogeneous material block to that prior to the recess. A small dimensional deviation, for example several tens of millimetres, is also possible.

This feature has the advantage, which is even more beneficial when the recess passes through the force transmission part from end to end, of preventing the presence, at a recess opening, of protruding edges abrading the lining of the sliding material.

Other characteristics and advantages of the invention can be clearly observed in the following description, which is given as a rough guide and in no way as a limited guide, with reference to the appended figures, in which:

FIG. 1 shows a perspective view of a cross-section of a support device according to the prior art,

FIGS. 2a, 2b and 2c each show a cross-sectional view of one embodiment of the support device according to the invention, and

FIGS. 3a and 3b each show half of a cross-sectional view of one embodiment of the support device according to the invention,

FIG. 4 shows a cross-sectional view of one embodiment of the support device according to the invention wherein the recess has been filled with a material,

FIG. 5 shows a perspective view of a convex part comprising a plurality of recesses according to one embodiment of the support device of the invention, and

FIG. 6 shows a perspective view of half of the support device according to one embodiment of the invention.

In the description below, each part of the device can be described as being positioned “on” or “below” another part of the device, which means that this part can also be positioned “directly” or “indirectly” (by interposition of an additional element) on or below said other part of the device. Moreover, the terms ‘lower’ and ‘upper’, ‘under’ and ‘on’, ‘below’ and ‘above’ used hereinbelow are considered to respectively indicate the side of the support of the support device and the side of the structure (bridge, building) that must be supported by the support device.

In the following description, the support device according to the invention is illustrated in the specific case of a spherical type support. It must be understood that this is only a simple illustration and that the characteristics of the invention are applicable to all types of structural support. In particular, pendular support devices form another family that can benefit from the teachings of the invention, for example friction pendulum sliding supports (FPS).

As illustrated in FIG. 6, the support device 100 according to the invention comprises a plurality of force transmission parts 1, 2a, 2b in mutual contact so as to transmit forces. These forces are directed in a predefined direction D; these forces are at least substantially directed in said direction. One of the two parts has a convex surface 1a, 1b and the other of the two parts has a concave surface 20a, 20b with a larger radius of curvature than said convex surface 1a, 1b. The convex surface 1a, 1b is in contact with the concave surface 20a, 20b in a contact area through which the forces are transmitted.

The direction D can be defined in different ways, substantially producing the same result, i.e. the definition, over its length, of the same part aligned with the contact area. The direction D is, for example, defined as orthogonal to a plane substantially including a contact area between two parts and as being centred in relation to this area. The direction D can also be defined as corresponding to a centre line of one of the force transmission parts 1, 2a, 2b or as corresponding more particularly to a centre line of the convex surface 1a, 1b or of the concave surface 20a, 20b of one of the force transmission parts 1, 2a, 2b. The direction D can also be defined as a mean line over an assembly of any lines having the aforementioned directions.

In the examples illustrated in FIGS. 1 and 6, the direction D is defined as a mean line over the three centre lines 11, 21a and 21b of the three force transmission parts 1, 2b, 2b. In the examples illustrated in FIGS. 2a, 2b, 2c and 4, strictly the same direction D is defined, regardless of which of the aforementioned definitions this illustration concerns.

Moreover, one of said convex and concave surfaces is lined with a sliding material 3. The latter is interposed as a lining or equivalently as a layer between two force transmission parts 1, 2a, 2b at least in their contact area, for accommodating the relative translational and/or rotational movements of these parts.

According to its widest acceptance, the support device is such that at least one of the two force transmission parts 1, 2a, 2b comprises a block of homogeneous material having at least one recess 4, 4a, 4b, 4c, 4d in a part aligned with the contact area along said direction D, or at least one part substantially aligned with the contact area along said direction D.

The scope of said part around the direction D depends on the scope of the contact area, itself dependent on the difference in the radius of curvature between the convex surface 1a, 1b and the concave surface 20a, 20b. This scope can be determined by the calculation according to the specific mechanical parameters of each structure equipped with a support device according to the invention.

In the examples described hereinbelow with reference to the figures, the force transmission parts 1, 2a, 2b comprise a convex part 1 and at least one support plate 2a including a concavity 20a. The convex part 1 is placed in and on the concavity 20a. The convex part 1 more particularly comprises a first convex surface 1a located opposite the concavity 20a of the support plate 2a.

These examples are non-limitative with regard to the scope of the appended claims, at least in the sense that the support plate can comprise a convex surface and the part located on this support plate can comprise a concavity located opposite the convex surface of the support plate.

In the examples illustrated in FIGS. 2a, 2b, 2c, 3a, 3b and 4, the convex part 1 further comprises, opposite its first convex surface 1a, a flat upper face. In the examples illustrated in FIGS. 5 and 6, the convex part 1 further comprises, opposite its first convex surface 1a, a second convex surface 1b.

In the first case, the convex part 1 can substantially have the shape of a spherical crown. In the second case, as illustrated in FIG. 5, the convex part 1 can include two parts substantially having the shape of spherical crowns or shells 10a, 10b. These parts are assembled together by a respective assembly surface 12a, 12b of each shell 10a, 10b. Shape variations of the convex part 1 are considered; for example, the convex part 1 can have an ovoid shape or an oblong cross-section.

As illustrated in FIG. 6, the support device 100 can further comprise a second support plate 2b placed on the convex part 1. In the case that the convex part 1 comprises an upper convex surface 1b, the second support plate 2b comprises a concavity 20b. The second support plate 2b is therefore placed on the convex part 1 such that the convex surface 1b is located opposite the concavity 20b.

The support plate 2a, 2b comprises a block of homogeneous material, this block capable of having the shape of a substantially flat parallelepiped or a disc. As illustrated in FIGS. 2a, 2b and 2c, a side 23a, 23b is, where relevant, hollowed out to form the concavity 20a, 20b. Another side 22a, 22b, opposite the side 23a, 23b is advantageously substantially flat.

According to one preferred embodiment illustrated in FIGS. 2a, 2b, 2c, 4 and 6, the recess 4 is formed at least:

- in the support plate 2a such that it is centred in relation to a centre line 21a of the concavity 20a and
- in the side 22a of the plate 2a opposite the concavity 20a.

The recess 4, 4a, 4b, 4c, 4d is used to reduce, potentially in a very localised manner, the stiffness of the support plate. Therefore, said plate can be more easily deformed when the support device 100 is under load. The contact area between the convex part 1 and the concavity 20a, 20b of the support device 2a, 2b is thus increased and the forces under load are more homogeneously distributed in the support device 100.

The global variation in stiffness obtained thanks to the recess 4, 4a, 4b, 4c, 4d depends on the shape and dimensions of this recess, however also on the stiffness, shape and dimensions of the block of homogeneous material constituting the recessed part and potentially on the stiffness, shape and dimensions of the blocks of homogeneous material constituting the other parts of the support device 100.

Moreover, the shape and dimensions of the recess 4 can be chosen according to the stiffness of the sliding material 3 and the shape and dimensions of the sliding material lining 3.

The shape of the recess 4, 4a, 4b, 4c, 4d is not particularly limited. However, shapes having axial symmetry are preferred insofar as the axis of symmetry of these shapes coincides with the centre line 11, 21a, 21b of the recessed part. Therefore, the recess can, for example, take on (i) the shape of a cylindrical bore as illustrated in FIGS. 2a, 2b and 2c, (ii) the shape of a spot facing as illustrated in FIGS. 3a and 3b, or additionally (iii) the shape of a bore made such that only the volume of an empty cylinder or a ring is recessed.

According to another preference, the recess 4, 4a, 4b, 4c, 4d does not comprise protruding edges on its walls and in its bottom so as to prevent the presence of preferential fracture areas of the recessed part. For example, a recess having, for the purpose of illustration, the aforementioned shapes is preferred in relation to a cubic recess. Similarly, each recess advantageously comprises a hollow between the surface of the bottom of the recess and its walls. As illustrated in FIGS. 3a and 3b, the hollow can have a constant variation of curvature or a constant radius.

The dimensions of the recess 4, 4a, 4b, 4c, 4d are limited by those of the recessed part. As illustrated in FIGS. 2a, 2b and 2c, the shape of the recess 4 can be cylindrical and the dimensions of this cylindrical shape can vary. In this instance, the recess 4 illustrated in FIG. 2a does not have the same diameter as the recess 4 illustrated in FIG. 2b, and the recess 4 illustrated in FIG. 2c does not have the same depth as the recesses 4 illustrated in FIGS. 2a and 2b.

It should be noted that, given that the shape and dimensions of the recess 4, 4a, 4b, 4c, 4d can vary in a continuous manner, a continuous variation of the stiffness of the recessed part can be obtained for a precise control of this variation.

The invention is not limited to a single recess 4 in the block of homogeneous material of a part of the support device 100. Indeed, as illustrated in FIG. 5, a plurality of recesses 4a, 4b, 4c, 4d can also be made in at least one part of the support device 100, in this instance in the convex part 1. The recesses of this plurality are therefore advantageously identical to each other, in their shape and dimensions, and distributed in a symmetrical manner in relation to a centre line of the concavity or convexity of the part considered, in this instance in relation to the axis 11.

In the example illustrated in FIG. 5, each recess 4a, 4b, 4c, 4d is formed at the level of the assembly surface 12b of the shell 10b of the convex part 1. Similarly, other recesses can be formed at the level of the assembly surface 12a of the shell 10a of the convex part 1. These other recesses can be identical or different, and can be located or not located opposite the recesses 4a, 4b, 4c, 4d illustrated. It should be noted that the action of making recesses in either one or both of the assembly surfaces 12a and 12b of the convex part 1 results in these recesses, provided that they are not through holes, not modifying the convex surfaces 1a and 1b of the convex part 1. This therefore prevents the presence, on these surfaces, of protruding edges capable of abrading the lining of sliding material during the relative movements of the convex part 1 and of the support plate 2a, 2b.

According to an additional feature, and as illustrated in FIGS. 2a, 2b and 5, at least one recess 4 is filled with a filler material 5. In the event that a plurality of recesses 4a, 4b, 4c, 4d is made in either of the parts, it is preferred, for the purposes of retaining symmetry, that the same filler material is used to fill all recesses forming the plurality.

The filler material 5 can have a stiffness that is less than the stiffness of the homogeneous material of the block. The filler material 5 can more particularly be chosen from the group comprising aluminium, potentially pure, bronze and ultra-high performance fibre-reinforced concrete, potentially steam-cured so as to limit endogenous shrinkage.

In order to prevent the presence of protruding edges capable of abrading the lining of sliding material during the relative movements of the parts with each other, the filler material 5 fills the recesses opening out at the level of said contact surfaces so as to at least make the face of the recessed part flush. The apparent surface condition of the filler material can more particularly be rectified, where necessary by machining, and more particularly to restore the shape and dimensions of the recessed block of homogeneous material to those prior to the recess.

Moreover, each recess can be a through hole. It is therefore advantageously filled so as to prevent the presence of protruding edges capable of abrading the lining of sliding material during the relative movements of the convex part 1 and of the support plate 2a, 2b. Within this limit, the filling of the recess with the filler material 5 can be incomplete.

It should be noted that the choice of the filler material and the partial or complete filling of the recess can be used to obtain a continuous variation of the stiffness of the recessed part over a wider range of values than those provided solely by the shape and dimension characteristics of this recess.

The support device 100 according to the invention advantageously allows for the precise control of the stiffness of each force transmission part 1, 2a, 2b to limit, or even prevent, the presence under load of a force concentration area in the parts. The load is therefore better distributed in the support device 100 and the dimensioning restrictions applicable to the support device are relaxed.

The solution proposed provides an alternative to that which, for many years, has consisted in developing new materials in order to produce satisfactory support devices in terms of the sliding of stresses and dimensioning. Moreover, these solutions are advantageously complementary to each other.

SUPPORT DEVICE WITH CONTROLLED STIFFNESS

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