Seismic protection system

Abstract

Seismic Protection System: An additional seismic protection system (10) for a structure comprising a lower foundation slab (2) and an upper foundation slab (3) with a set of seismic supports (4) between the two, designed to protect the structure against the occurrence of a vertical displacement beneath it, leading to a subsidence of the lower foundation slab (2). This protection system includes a set of two-state support devices (11) arranged between the two foundation slabs, configured to automatically switch, in reaction to the subsidence of the lower foundation slab (2), from a retracted standby state where the support of the upper foundation slab (3) is ensured primarily by the seismic supports (4), to an active deployed state where the force applied by the support devices (11) on the upper foundation slab (3) is sufficient to compensate for the loss of effect of the seismic supports (4). Figure for the abbreviation: Fig. 6

Description

Title of the invention: Seismic protection system technical field

[0001] The present invention relates to seismic protection systems. Previous technique

[0002] It is known to protect structures against seismic risk by constructing a double foundation slab and interposing between the two seismic supports in the form of concrete pads surmounted by an elastically deformable pad, typically made of elastomer reinforced.

[0003] The lower slab rests on the ground or foundations of the structure while the upper slab supports the rest of the structure.

[0004] In the event of horizontal seismic shocks, the pads of the seismic supports deform elastically and attenuate the effect of the earthquake.

[0005] However, in such a configuration, the structure is not protected against the effects of the appearance, during an earthquake, of a fault beneath the structure exhibiting a vertical displacement with an amplitude that can reach several tens of centimeters. Such a fault creates a discontinuity in the ground beneath the structure, which can cause the foundation slabs to tilt and result in very significant damage.

[0006] Applications RU2585768, FR2680809, FR253444, KR101915707, RU2512054, BE751034, DE2035012 and US4554767 describe various seismic protection systems. However, none of them is suitable for protecting a building against the risk of a fault appearing beneath the structure.

[0007] For the purposes of this invention, "fault" means a reverse or normal fault, which creates a difference in elevation in the ground at the level of the structure. One side of the fault may remain stationary while the other rises, or one side may remain stationary while the other descends, or one side may rise while the other descends. Description of the invention

[0008] The invention aims to provide a safe operating seismic protection system, enabling protection against the above-mentioned risk of a new or existing structure.

[0009] When installed on an existing structure, the system must not modify the the behavior of the structure during a standard earthquake, and in particular must not significantly alter the structure's response to the earthquake.

[0010] Not knowing the position of a possible fault, the system must be able to adapt to any possible position.

[0011] Since the speed at which a fault appears is on the order of a few seconds, the system must be able to react quickly, in particular in less than one second. Summary of the invention

[0012] The invention thus relates to an additional seismic protection system for a structure comprising a lower foundation slab and an upper foundation slab with a set of seismic supports between the two, this protection system being intended to protect the structure against the occurrence of a vertical displacement below it, causing a subsidence of the lower foundation slab and the loss of effect of part of the seismic supports, this additional protection system comprising a set of two-state support devices arranged between the two foundation slabs, configured to automatically switch, in reaction to the subsidence of the lower foundation slab, from a retracted standby state where the support of the upper foundation slab is ensured essentially by the seismic supports to an active deployed state where the force applied by the support devices on the upper foundation slab is sufficient to compensate for the loss of effect of the seismic supports.

[0013] Such an additional system is compatible with its installation on an existing structure.

[0014] The support devices can be distributed between the foundation slabs to cover any potential location of a fault under the structure.

[0015] The support devices do not significantly alter, in the standby state, the structure's response to a conventional earthquake, and the seismic supports can perform their function effectively. Therefore, it is not necessary to recalculate the structure's behavior under a flawless earthquake.

[0016] The deployment of the holding devices can be carried out in the active state under the effect of hydraulic or pneumatic pressure. This requires that a pressure source be available at the time of system activation.

[0017] Alternatively, the deployment of the holding devices is carried out in the active state by the production of a gas through a chemical reaction. Preferably, this chemical reaction is a decomposition reaction, in particular of a solid, preferably sodium azide. This allows for the very rapid production of a large quantity of gas.

[0018] Preferably, each retaining device comprises a body defining a chamber in which a movable part moves under the effect of pressure in the chamber. This body may be a single piece or formed by the assembly of several parts, particularly metallic ones.

[0019] The moving part of each device can be used to bear against the upper foundation slab in the standby state, and each device can be configured to The movement of the moving part beyond a predefined stroke in response to the subsidence of the lower foundation slab triggers the device's activation. This arrangement offers the advantage of allowing for very simple automatic and passive activation of each support device locally exposed to relative subsidence of the lower foundation slab.

[0020] The upper slab may include wedges against which the moving parts bear. Each of these wedges may include a flat jack into which a cement grout or resin has been injected and which has hardened. This system ensures pre-compression of the moving parts.

[0021] The predefined stroke before triggering can be greater than or equal to 5mm. Thus, untimely triggering of the support devices is avoided under the effect of small displacements of the structure of the work, linked to expansion for example, or during a "standard" earthquake, linked to variations in the crushing of the seismic supports.

[0022] In exemplary embodiments, the retaining devices each comprise at least one seal that, in the standby state of the device, is applied between the moving part and the body, and an inlet for a pressurized fluid (liquid or gas) that opens into a space delimited by said seal. Thus, the pressure exerted by the fluid on the moving part in the standby state is limited to a portion of the cross-section of the moving part. The seal ceases to provide a tight seal between the moving part and the body when the moving part has moved a predefined distance, allowing the pressurized fluid to then act on substantially the entire cross-section of the moving part. The upward thrust force on the moving part, which is directly proportional to the cross-section exposed to the pressurized fluid, is therefore relatively low in the standby state and becomes much greater once the seal ceases to function.This avoids exerting significant pressure on the upper foundation slab in the standby state, which could alter the behavior of the seismic supports in the event of an earthquake.

[0023] The seal is, for example, supported by an annular rib projecting from the bottom of the chamber and extending around the pressurized fluid inlet. Standby sealing can be ensured by such a seal and by an additional seal located on the edge of the rib and axially compressed between the rib and the moving part during standby. The moving part may include a housing into which the annular rib can engage during standby, the aforementioned seal being interposed between the lateral surface of this housing and the rib. The additional seal may be interposed between the bottom of the housing and the rib.

[0024] In exemplary embodiments, the body of the retaining devices forms a pressurized gas reservoir under the chamber. This can simplify the installation of the This system avoids the need for large-diameter pressurized fluid supply pipes. In this case, the pressure on the moving part can be exerted by the gas itself, rather than by a pressurized hydraulic fluid such as oil.

[0025] In other embodiments, the holding devices are connected to hydraulic fluid lines maintained under pressure, preferably by means of a compressed gas reservoir, preferably dried air or nitrogen. This reservoir can be associated with a hydraulic fluid accumulator. This allows for relatively compact holding devices, as the hydraulic reservoir and accumulator are separate from them and preferably installed on the surface to avoid any risk related to leaks, particularly of nitrogen.

[0026] Each retaining device can be equipped with a purge valve, and preferably a pressure gauge, to allow manual or automatic purging of the pressure chamber outside the aforementioned seal, which limits the area exposed to the fluid in standby mode. This purging prevents the accumulation of pressure resulting from seepage through the seal(s) over the long term.

[0027] Alternatively, the moving part drives an ignition device that ignites at least one pyrotechnic charge, causing a decomposition reaction of a solid, preferably sodium azide or other types of solids used for this purpose, by moving beyond a predefined stroke. This can eliminate the need for pipelines to transport a pressurized fluid.

[0028] In such a case, each retaining device may include a spring that exerts pressure on the moving part in contact with the upper base plate.

[0029] Preferably, the system includes a non-return mechanism that prevents reverse movement of the moving part after activation of the retaining device. Thus, in the event of a pressure drop in the chamber, the descent of the moving part is prevented. This non-return mechanism may include a movable locking element that acts by wedging in the direction of the return of the moving part within the body of the retaining device.

[0030] Preferably, each support device is connected by a hinge to the lower foundation slab. This allows for lateral movement of the support devices during a conventional earthquake and reduces the impact of the presence of the support devices on the structure's behavior during the earthquake. The movable part may include an elastically deformable element, such as an elastomer pad secured at its upper end, allowing it to accommodate the horizontal movements of the upper foundation slab during an earthquake, even when the support device is in standby mode.

[0031] Preferably, the support devices, in the standby state, provide less than 10% of the forces absorbed by the seismic supports. Thus, the support devices do not unduly disrupt the behavior of the structure during an earthquake, nor its behavior in service.

[0032] The system according to the invention can be installed during the construction of a new structure.

[0033] It can still be installed on an existing structure.

[0034] The invention also relates, according to another aspect, to a method of protection of a structure against the risk linked to the appearance of a fault under it, the structure comprising a lower slab and an upper slab with a set of seismic supports between the two, method in which an additional protection system according to the invention, as defined above, is installed between the slabs.

[0035] The invention also relates to a holding device as such.

[0036] This retaining device may have any of the above-mentioned characteristics with respect to the system, considered individually or in combination.

[0037] This retaining device may thus comprise a body and a moving part that slides in a sealed manner within the body, and at least one seal that applies in the standby state of the device between the moving part and the body, and an inlet for a pressurized fluid that opens into a space delimited by said seal, such that the pressure exerted by the fluid on the moving part in the standby state is limited to a portion of the cross-section of the moving part, the seal ceasing to apply a sealed application between the moving part and the body when the moving part has moved a predefined distance, allowing the pressurized fluid to then apply pressure to substantially the entire cross-section of the moving part. The moving part may comprise an elastically deformable element in its upper part, and the body may comprise a hinge in its lower part.

[0038] Alternatively, the retaining device comprises a body and a movable part sliding in a sealed manner in a chamber defined by the body, and the movable part drives a firing device which causes the ignition of at least one pyrotechnic charge located in the chamber, causing a decomposition reaction of a solid, preferably sodium azide, by moving beyond a predefined stroke. Brief description of the drawings

[0039] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the accompanying drawing, in which:

[0040] [Fig. 1] [Fig. 1] schematically and partially represents an example of a building according to the prior art, equipped with seismic supports,

[0041] [Fig.2] [Fig.2] illustrates the behavior of seismic supports during an earthquake,

[0042] [Fig.3] [Fig.3] illustrates the effects of the appearance of a fault under the building,

[0043] [Fig.4] [Fig.4] represents a building equipped with a protection system additional according to the invention,

[0044] [Fig.5] Figure 5 illustrates the behavior of the system according to the invention during a conventional earthquake,

[0045] [Fig.6] [Fig.6] illustrates the behavior of the system according to the invention in the event of the appearance of a fault under the structure,

[0046] [Fig.7A] [Fig.7A] represents in isolation an example of a device for maintaining a standby state,

[0047] [Fig. 7B] [Fig. 7B] represents the device of [Fig. 7A] after triggering,

[0048] [Fig. 8] [Fig. 8] illustrates a power supply variant of a holding device,

[0049] [Fig. 9] [Fig. 9] represents an alternative embodiment of a holding device,

[0050] [Fig. 10] [Fig. 10] represents another alternative embodiment of a holding device, and

[0051] [Fig. 11] [Fig. 11] is a longitudinal section of an alternative embodiment of a retaining device. Description of the implementation methods

[0052] A building 1 comprising a lower foundation 2 and an upper foundation 3 resting on seismic supports 4 is partially represented in [Fig.1].

[0053] Foundations 2 and 3 are typically reinforced concrete slabs.

[0054] The supports 4 are in the form of blocks 6, for example made of reinforced concrete, fixed below the foundation 2, and fitted above with an elastically deformable seismic insulator 7, comprising a confined elastomeric material, in a manner known per se.

[0055] In the presence of horizontal vibrations during an earthquake, the insulators 7 can deform elastically, as illustrated in [Fig.2], to dampen the effects of the earthquake on the structure of the building.

[0056] During an earthquake, the isolation provided by the supports 4 thus makes it possible, on the one hand, to reduce the vibration frequencies of the structure and, on the other hand, to increase damping. If necessary, they can be combined with additional damping systems to provide further damping, the supports primarily affecting the natural vibration frequencies of the structure.

[0057] In the event of a fault F appearing under the building, as illustrated in [Fig.3], the vertical movement detaches some supports and over-compresses other supports, causing potentially very significant damage to the structure.

[0058] Figure 4 shows an example of an additional protection system 10 according to the invention.

[0059] This system 10 comprises a set of support devices 11 distributed between the foundation slabs 2 and 3 between the seismic supports 4.

[0060] For example, as illustrated, there are at least two retaining devices 11 on either side of each support 4.

[0061] The holding devices 11 can take two states, namely a standby state and an active state.

[0062] In the standby state, which corresponds to [Fig.4], the retaining devices 11 do not apply any force on the upper slab 3 or apply a force that is weak, compared to that exerted by the supports 4.

[0063] The force exerted by each holding device 11 in the standby state can thus correspond to less than 10% of the force R exerted by an adjacent support 4.

[0064] Each retaining device 11 can be fixed below the lower slab 2 by means of a joint 12, for example a ball joint, and bear against the upper base 3 by means of an insulator 13, comprising for example a confined elastomeric material. The joint 12 may also be formed of an elastically deformable element allowing a certain angular deflection.

[0065] Each retaining device includes a movable part 16 which can move relative to a body 15, which defines a pressure chamber 14. This movable part 16 moves like a piston in the body 15, under the effect of a pressure in the chamber.

[0066] In the event of a conventional earthquake and horizontal vibrations of the structure, the support devices 11 can accompany, while remaining in standby mode, the movement of the upper slab 3 as illustrated in [Fig.5], and thus not excessively modify the behavior of the structure and the action of the supports 4.

[0067] In the event of the appearance of a fault under the building, as illustrated in [Fig.6], the ground may undergo a vertical displacement which affects a part of the lower foundation slab 2.

[0068] In the example of this [Fig.6], the right part of the lower slab 2 slumps relative to the left part, and thus moves away from the upper slab 3. The supports 4 located on the right part of the lower slab cease to support the upper slab 3.

[0069] The retaining devices 11 which are exposed to this increase in the spacing between the foundations 2 and 3 are arranged to change state and deploy in order to exert a force aimed at compensating for the loss of action of the corresponding supports 4.

[0070] Each support device 11 located on the right side of the lower slab 2 thus exerts a force substantially equal to R / 2 in the example considered, which prevents the upper slab 3 from sagging.

[0071] The moving parts 16 of the devices 11 located around a support 4 exert together a force close to that resisted at rest by this support. As a result, the distribution of loads under the structure after triggering is only slightly modified by compared to the initial distribution, this greatly limits the stresses and deformations of the upper foundation slab 3, which can thus remain intact with little displacement.

[0072] The retaining devices 11 are arranged to trigger only after a displacement of the movable part 16 relative to the body 15 greater than a given threshold, this threshold being that for which the deformation of the upper base is without major consequences, this threshold being for example between 5mm and 10mm, for example 5mm.

[0073] Thus, small amplitude vertical movements which may appear during an earthquake under the effect of the variation of the crushing of the supports 4 due to fluctuations in the vertical force, on the order of less than 5mm, do not cause the change of state of the devices 11.

[0074] The triggering of the retaining devices 11 is preferably carried out in a totally passive manner, as a mechanical response to the increase in the local spacing between the foundations 2 and 3. The energy required to actuation the retaining devices 11 is preferably released in a very short time, advantageously less than 1s.

[0075] The force exerted by each support 4 is, for example, between 100 and 1000 t. The force applied by each retaining device 11 in the active state is, for example, between 50 t and 500 t, being, for example, approximately 200 t. The cross-sectional area of ​​the moving part 16 exposed to pressure in the chamber 14, in the activated state, is, for example, on the order of 0.1 m², which corresponds to a diameter of approximately 350 mm. The pressure in the chamber 14 is, for example, on the order of 200 bar, being chosen according to the dimensions of the retaining device, its resistance, and the force to be produced.

[0076] The retaining devices 11 can be made in various ways to achieve this result.

[0077] In the example of Figures 7A and 7B, the movement of the moving part 16 is achieved with a hydraulic fluid 18 contained in a hydraulic fluid accumulator pressurized by a reservoir 17 of a compressed gas, for example nitrogen or dried air. The reservoir 17 can contain, for example, approximately 400 liters of nitrogen compressed to more than 200 bar.

[0078] The body 15 of the retaining device 11 has an orifice 20 for supplying the pressurized fluid which opens into the bottom of the chamber 14, in the center thereof.

[0079] The orifice 20 is for example defined by an annular rib 21.

[0080] The movable part 13 has, for example, as illustrated, a cylindrical housing 24 in which the rib 21 engages when the device is in the standby state, as illustrated in [Fig.7A].

[0081] The movable part 13 can carry an annular sealing gasket 22 which applies itself to the rib 21 in this state. Alternatively, the gasket 22 is carried by the rib. A Sealing joint 23 can also be provided at the free end of the rib, to be applied in the bottom of the housing 24.

[0082] Thus, only a section corresponding substantially to the bottom of the housing 24 is exposed to the pressure of the hydraulic fluid, in the standby state, as illustrated in [Fig.7A],

[0083] The hydraulic fluid 18 thus exerts a moderate upward thrust on the moving part 16, due to the limited section exposed to pressure.

[0084] A pressure gauge 38 may be provided to monitor the supply pressure of the device, and a drain valve 39 equipped with a pressure gauge 40 may be provided to monitor the pressure in the chamber 14 outside the seal 22 in standby mode. If the pressure rises over time due to a leak, this pressure can be reduced by opening the drain valve 39.

[0085] A wedge 30 can be provided between the insulator 13 and the upper slab 3, in order to allow the movable part 16 to press against this slab in the standby state while being blocked by it.

[0086] This wedge 30 is for example a flat jack into which a cement grout or resin is injected.

[0087] When the lower slab 2 moves away from the upper slab 3 in the event of an earthquake, and the movable part 16 moves sufficiently upwards relative to the body 15, the seal 22 ceases to play its role, for example by ceasing to apply itself to the rib 21, and the hydraulic fluid 18 can spread into the chamber 14, as illustrated in [Fig.7B],

[0088] The moving part 16 is then exposed over substantially its entire section to the pressure of the hydraulic fluid 18, which makes it possible to exert a much greater thrust force on the moving part 16.

[0089] The internal section of the hydraulic fluid supply pipe(s) 34 to the pressure chamber 14 of the holding device 11 is chosen so that the fluid flow rate is sufficient to obtain the desired responsiveness in the event of an earthquake.

[0090] Each holding device 11 can be equipped with its own pressure tank and hydraulic fluid accumulator 18. Alternatively, several holding devices 11 are supplied by the same pressure tank and hydraulic fluid accumulator.

[0091] In the example of [Fig.8], at least one reservoir with hydraulic fluid accumulator is common to several support devices 11, and can be connected to at least one primary hydraulic fluid distribution line 35, fixed under the upper slab 3, as illustrated.

[0092] Secondary pipes 36 made up for example of flexible hoses are connected to the primary pipe 35 to supply each of the holding devices 11.

[0093] The internal diameter of a secondary pipe 36 is, for example, between 30 and 80 mm, being, for example, on the order of 50 mm. Such a diameter allows, for example, 20 l of oil to be delivered in 1 second at a pressure of 200 bar. The primary pipe 35 supplies, for example, approximately twenty retaining devices 11, and its internal diameter is, for example, greater than or equal to 225 mm.

[0094] Each of the secondary pipes 36 can be equipped with a pilot-operated valve 37 to close the circuit in the event of a hose rupture. This valve 37 can close automatically if the pressure differential upstream and downstream of the valve exceeds a certain value.

[0095] As in the example in Figures 7A and 7B, a pressure gauge 38 can be provided to monitor the supply pressure of the device, and a drain valve 39 equipped with a pressure gauge 40 can be provided to monitor the pressure in the chamber 14 outside the seal 22 in the standby state. If the pressure rises over time due to a leak, this pressure can be reduced by opening the drain valve 39.

[0096] In the example of [Fig.9], the pressurized reservoir 17 is located in the extension of the chamber 14 and below it, the body 15 of the device comprising for example a cylinder of revolution whose upper part serves to guide the movable part 16 and the lower part forms the lateral wall of the reservoir 17.

[0097] In this variant, the pressurized fluid is for example a compressed gas such as dried air or nitrogen.

[0098] A partition 45 separates the chamber 14 and the reservoir 17. This partition 45 is crossed by a conduit 46, the upper part of which plays the role of the aforementioned rib 21.

[0099] Seals 48 ensure the tight sliding of the moving part 16 in the body 15.

[0100] The latter can be mounted at its base on an elastically deformable pad 50 which acts as a joint by allowing a slight angular movement of the retaining device 11.

[0101] The outer diameter of the moving part 16 is, for example, approximately 360 mm. In its standby state, the force applied by the moving part 16 on the base 3 is, for example, approximately 20 t. This force can be increased tenfold when the device 11 is activated by disengaging the housing 24 from the conduit 46.

[0102] The variant illustrated in [Fig. 10] differs from the previous ones in that the pressure is created in the chamber 14 of the device by the decomposition of at least one charge 60 of a solid such as sodium azide.

[0103] An ignition device 62, symbolized by a point in [Fig. 10], moves with the movable part 16 to ignite the charge 60 after a predefined upward stroke, for example, approximately 5 mm. This ignition device 62 includes, for example, an electrical contactor that moves with the movable part 16 and applies a current to the charge 60 upon contact, causing it to heat up and decompose.

[0104] The retaining device 11 may include, as illustrated, a spring 70 which works in compression and pushes the movable part 16 upwards; thus, the latter can move upwards in the event of subsidence of the lower slab 2, and the firing device 62 can fulfill its function.

[0105] The spring 70 is interposed axially within the chamber 14 between a shoulder 72 of the body and the bottom 73 of the moving part 16.

[0106] One or more additional charges 75 of said solid can be actuated by the continued movement of the ignition device 62 to successively cause the release of additional volumes of gas, and thus compensate for the resulting increase in the volume of the chamber 14, which tends to reduce the pressure in it.

[0107] It may be advantageous to equip each retaining device 11 with a mechanism which prevents a return movement of the moving part 16, in order to lock the moving part in place in the event that the earthquake continues after the appearance of the fault or in the event of a drop in pressure in the chamber, due for example to a loss of sealing.

[0108] This mechanism can be implemented in various forms, and act for example by a wedging effect or by a ratchet effect.

[0109] By way of example, a retaining device 11 equipped with such a mechanism is shown partially in [Fig.1 1].

[0110] The anti-return mechanism includes in the example of [Fig.1 1] at least one locking piece 80 which is axially movable upwards against the return action of at least one spring 81.

[0111] This locking piece 80 has a wedge shape, and it is housed between the cylindrical surface 84 of the movable part 16 and an inclined surface 85 of an annular piece 86 surrounding the movable part.

[0112] The inclination of the surface 85 corresponds substantially to that of the face opposite the locking piece 80, such that a downward movement of the moving part 16 tends to pull the locking piece downwards and cause it to become wedged between the moving part 16 and the annular part 85, which blocks the continuation of the downward movement of the moving part 16.

[0113] However, the locking piece 80 can rise slightly, accompanying the exit movement of the moving part. When stopped, the locking piece 80 is pushed back by the springs 81 towards the bottom of the housing formed between the movable part 16 and the annular piece 86.

[0114] The locking of the moving part 16 in the active state prevents the risk of it descending in the event of a drop in pressure in the chamber 14.

[0115] Of course, the invention is not limited to the examples just described.

[0116] For example, the energy required for the operation of the holding devices can be released in another way, in particular by using a chemical reaction other than the decomposition of sodium azide. The chemical reaction may or may not be a combustion reaction, preferably being non-explosive.

[0117] The force can still be exerted on the upper floor in the standby state by means of a spring, rather than with the pressure of a hydraulic fluid or a gas on a portion of the cross-section of the moving part.

[0118] The return of horizontal forces in the areas or the support devices 11 have been triggered can be ensured by additional devices of the shock absorber type.

[0119] In [Fig.6] we see that one side of the fault has risen and the other has fallen, but we do not go out of the scope of the present invention when it is the reverse or when one of the sides has not moved and the other has fallen or has risen.

[0120] In conclusion, the invention makes it possible to provide additional seismic protection to existing sensitive new or existing structures which have already been subject to seismic protection consisting of the construction of a double foundation slab with interposition of seismic supports between the two foundation slabs.

[0121] This additional protection system makes it possible to protect the structure from the effects of the appearance, during an earthquake, of a fault under the structure presenting a vertical displacement of an amplitude that can reach several tens of cm.

[0122] The two-state holding devices according to the invention, before triggering, marginally modify the operation of the structure and, after triggering, compensate for all or most of the forces borne by each seismic support.

[0123] The fact of articulating the lower part of the support devices on the lower slab and providing an elastically deformable element in the upper part advantageously makes it possible not to unduly hinder the horizontal movements of the structure and to avoid a significant change in the frequencies and modes of vibration of the structure.

Claims

Demands

1. An additional seismic protection system (10) for a structure comprising a lower foundation slab (2) and an upper foundation slab (3) with a set of seismic supports (4) between the two, this protection system being intended to protect the structure against the occurrence of a vertical displacement beneath it, resulting in a subsidence of the lower foundation slab (2) and the loss of effect of part of the seismic supports (4), this additional protection system comprising a set of two-state support devices (11) arranged between the two foundation slabs, configured to automatically switch, in reaction to the subsidence of the lower foundation slab (2), from a retracted standby state where the support of the upper foundation slab (3) is ensured by the seismic supports (4) to an active deployed state where the force applied by the support devices (11) on the upper foundation slab (3) is sufficient to compensate for the loss of effect of the seismic supports. (4).

2. System according to claim 1, the deployment of the holding devices (11) taking place in the active state under the effect of hydraulic or pneumatic pressure.

3. System according to claim 1, the deployment of the holding devices (11) taking place in the active state under the effect of the production of a gas by a chemical reaction.

4. System according to claim 3, the chemical reaction being a decomposition reaction, in particular of a solid (60), preferably of sodium azide.

5. System according to any one of the preceding claims, the retaining devices (11) each comprising a body (15) defining a chamber (14) in which a movable part (16) moves under the effect of the pressure in the chamber.

6. System according to claim 5, the moving part (16) of each device being forced to come to rest against the upper slab (3) in the standby state, and each device (11) being configured so that the displacement of the moving part beyond a predefined stroke in response to the sagging of the lower slab (2) causes the device (11) to move into the active state.

7. System according to claim 6, the predefined stroke being greater than or equal to 5mm.

8. System according to claims 2 and 5, the retaining devices (11) each comprising at least one seal (22) which applies in the standby state of the device between the moving part (16) and the body (15), and an inlet of a pressurized fluid (18) which opens into a space delimited by said seal (22), such that the pressure exerted by the fluid (18) on the moving part (16) in the standby state is limited to a part of the cross-section of the moving part, the seal (22) ceasing to apply in a watertight manner between the moving part (16) and the body (15) when the moving part has moved a predefined stroke, allowing the pressurized fluid (18) to apply over the entire cross-section of the moving part (16).

9. System according to claim 8, the seal (22) being carried by an annular rib (21) projecting into the bottom of the chamber (14) and extending around the inlet of the pressurized fluid, or by the movable part (16).

10. System according to any one of claims 8 and 9, the body (15) of the retaining devices forming under the chamber (14) a reservoir (17) of pressurized gas.

11. System according to any one of claims 8 and 9, the holding devices (11) being connected to lines of a hydraulic fluid (18) kept under pressure, preferably using a reservoir of a compressed gas, preferably dried air or nitrogen.

12. System according to any one of claims 8 to 11, each retaining device (11) being equipped with a purge valve, and preferably a pressure gauge, to allow manual or automatic purging of the pressure chamber outside the seal (22).

13. System according to claims 4 and 6, the moving part (16) driving an ignition device (62) which causes the ignition of at least one pyrotechnic charge causing a decomposition reaction of a solid (60), preferably sodium azide, by moving beyond a predefined stroke.

14. System according to claim 13, comprising a spring (70) exerting pressure on the movable part (16) in support against the upper base (3).

15. System according to any one of the preceding claims, including a connection to claim 5, comprising an anti-return mechanism (80, 81, 86) prohibiting reverse movement of the moving part (16) after activation of the holding device.

16. System according to any one of the preceding claims, each retaining device (11) being connected by a joint (12) to the lower base.

17. System according to any one of the preceding claims, the support devices ensuring in the standby state less than 10% of the forces taken up by the seismic supports (4).

18. A method for protecting a structure against the risk of the appearance of a fault (F) under it, the structure comprising a lower slab (2) and an upper slab (3) with a set of seismic supports (4) between the two, a method in which an additional protection system (10) as defined in any one of the preceding claims is installed between the slabs.

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