Earthquake protection system

Abstract

Seismic protection system Additional seismic protection system (10) for a structure comprising a lower raft (2) and an upper raft (3) with a set of seismic supports (4) between the two, aimed at protecting the structure against the occurrence of a vertical detachment beneath it causing a collapse of the lower raft (2), this protection system comprising a set of two-state holding devices (11) arranged between the two rafts, configured to automatically switch, in response to the collapse of the lower raft (2), from a retracted standby state where the upper raft (3) is held essentially by the seismic supports (4) to an active deployed state where the force applied by the holding devices (11) on the upper raft (3) is sufficient to compensate for the loss of effect of the seismic supports (4). Figure for the abstract: Fig. 6

Description

Title of the invention: Earthquake protection system Technical field

[0001] The present invention relates to earthquake protection systems. Prior art

[0002] It is known to protect structures against seismic risk by creating a double raft and interposing between the two earthquake-resistant supports in the form of concrete blocks topped with an elastically deformable pad, typically made of fretted elastomer.

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

[0004] In the event of horizontal seismic tremors, the pads of the earthquake-resistant 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 under the structure presenting a vertical detachment of an amplitude which can reach several tens of cm. Such a fault creates a discontinuity of the ground under the structure, which can cause the foundations to tilt and cause very significant damage.

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

[0007] By "fault", it is necessary to understand in the sense of the present invention a reverse or normal fault, which creates a difference in level on the ground at the level of the structure. One side of the fault may not move and the other rise, or one side may not move and the other descend, or one side may rise while the other descends. Statement of the invention

[0008] The invention aims to propose a seismic protection system with safe operation, making it possible to ensure protection against the risk mentioned above of a new or existing structure.

[0009] When installed on an existing structure, the system must not modify the behavior of the structure during a standard earthquake, and in particular must not significantly modify the response of the structure 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 of the order of a few seconds, the system must be able to react quickly, particularly in less than a second. Summary of the invention

[0012] The invention thus relates to an additional seismic protection system for a structure comprising a lower raft and an upper raft with a set of seismic supports between the two, this protection system aiming to protect the structure against the occurrence of a vertical detachment beneath it causing a collapse of the lower raft and the loss of effect of a portion of the seismic supports, this additional protection system comprising a set of two-state support devices arranged between the two rafts, configured to automatically switch, in reaction to the collapse of the lower raft, from a retracted standby state where the upper raft is essentially held in place by the seismic supports to an active deployed state where the force applied by the support devices to the upper raft 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 retaining devices can be distributed between the rafts to cover any potential location of a fault under the structure.

[0015] The support devices do not excessively modify, in the standby state, the response of the structure to a conventional earthquake, and the earthquake-resistant supports can play their role effectively. It is therefore not necessary to recalculate the behavior of the structure under a faultless 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 activation of the system.

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

[0018] Preferably, the holding devices each comprise a body defining a chamber in which a movable part moves under the effect of the pressure in the chamber. This body may be in one piece or formed by the assembly of several parts, in particular metal parts.

[0019] The movable part of each device can be urged to bear against the upper raft in the standby state, and each device can be configured to that the movement of the movable part beyond a predefined stroke in response to the subsidence of the lower raft causes the device to switch to the active state. Such an arrangement has the advantage of allowing very simple automatic and passive activation of each holding device locally exposed to a relative subsidence of the lower raft.

[0020] The upper raft may include shims against which the moving parts rest. These shims may each 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 travel before triggering can be greater than or equal to 5 mm. This prevents untimely triggering of the holding devices under the effect of small movements of the structure of the work, linked to expansion for example, or during a “standard” earthquake, linked to variations in crushing of the earthquake-resistant supports.

[0022] In exemplary embodiments, the holding devices each comprise at least one seal which is applied in the standby state of the device between the mobile part and the body and an inlet of a fluid (liquid or gas) under pressure which opens into a space delimited by said seal, such that the pressure exerted by the fluid on the mobile part in the standby state is limited to a part of the section of the mobile part, the seal ceasing to be applied in a sealed manner between the mobile part and the body when the mobile part has moved a predefined stroke, allowing the pressurized fluid to then be applied over substantially the entire section of the mobile part. The upward thrust force of the mobile part, which is directly proportional to the section exposed to the pressurized fluid, is thus relatively low in the standby state, and becomes much greater as soon as the seal ceases to play its role.This avoids exerting significant pressure on the upper raft in the standby state, which could modify the behavior of the earthquake-resistant supports in the event of an earthquake.

[0023] The seal is for example carried by an annular rib forming a projection in the bottom of the chamber and extending around the arrival of the pressurized fluid. The seal in the standby state can be ensured by such a seal and by an additional seal present on the edge of the rib and compressed axially in the standby state between the rib and the moving part. The moving part can comprise a housing in which the annular rib can engage in the standby state, the aforementioned seal being able to be interposed between the lateral surface of this housing and the rib. The additional seal can be interposed between the bottom of the housing and the rib.

[0024] In exemplary embodiments, the body of the holding devices forms a pressurized gas reservoir under the chamber. This can simplify the installation of the system by avoiding the need for large internal diameter pressurized fluid supply pipes. In this case, the pressure on the moving part can be exerted by the gas itself and not by a hydraulic fluid such as oil, under pressure.

[0025] In other embodiments, the holding devices are connected to pipes of a hydraulic fluid maintained under pressure, preferably using a reservoir of a compressed gas, preferably dried air or nitrogen. This reservoir can be associated with a hydraulic fluid accumulator. This can make it possible to have relatively compact holding devices, the reservoir and the hydraulic accumulator being separated from them and preferably installed on the surface to avoid any risk linked to leaks, particularly of nitrogen.

[0026] Each holding device may 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 section exposed to the fluid in the standby state. This purging makes it possible to avoid the accumulation of pressure resulting from seepage through the seal(s) over the long term.

[0027] Alternatively, the moving part drives a firing device which causes the firing of at least one pyrotechnic charge causing a decomposition reaction of a solid, preferably sodium azide or other types of solids used for this type of use, by moving beyond a predefined stroke. This can make it possible to avoid the installation of pipelines for transporting a pressurized fluid.

[0028] In such a case, each holding device may comprise a spring urging the movable part to bear against the upper raft.

[0029] Preferably, the system comprises a non-return mechanism preventing reverse movement of the movable part after activation of the holding device. Thus, in the event of a pressure drop in the chamber, the movable part is prevented from descending. This non-return mechanism may comprise a movable blocking element acting by wedging in the direction of return of the movable part into the body of the holding device.

[0030] Preferably, each holding device is connected by a joint to the lower raft. This can allow lateral movement of the holding devices during a conventional earthquake, and reduces the impact of the presence of the holding devices on the behavior of the structure during the earthquake. The movable part can comprise an elastically deformable element such as an elastomer pad strapped to its upper end, making it possible to accompany the horizontal movements of the upper raft in the event of an earthquake, and while the holding device is in the standby state.

[0031] Preferably, the holding devices ensure in the standby state less than 10% of the forces taken up by the earthquake-resistant supports. Thus, the holding devices do not unduly disrupt the behavior of the structure during an earthquake, nor the 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 of its aspects, to a method of protection of a structure against the risk linked to the appearance of a fault beneath it, the structure comprising a lower raft and an upper raft with a set of earthquake-resistant supports between the two, a method in which an additional protection system according to the invention is installed between the rafts, as defined above.

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

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

[0037] This holding device may thus comprise a body and a movable part sliding in a sealed manner in the body, and at least one seal which is applied in the standby state of the device between the movable part and the body and an inlet of a pressurized fluid which opens into a space delimited by said seal, such that the pressure exerted by the fluid on the movable part in the standby state is limited to a part of the section of the movable part, the seal ceasing to be applied in a sealed manner between the movable part and the body when the movable part has moved a predefined stroke, allowing the pressurized fluid to then be applied over substantially the entire section of the movable part. The movable part may comprise an elastically deformable element in the upper part, and the body may comprise an articulation in the lower part.

[0038] Alternatively, the holding 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 firing 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 may be better understood by reading the detailed description which follows, non-limiting examples of its implementation, and by examining the attached drawing, in which:

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

[0041] [Fig.2] [Fig.2] illustrates the behavior of earthquake-resistant 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] [Fig.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 the standby state,

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

[0048] [Fig.8] [Fig.8] illustrates an alternative supply 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 holding device. Description of the embodiments

[0052] [Fig.l] partially shows a building 1 comprising a lower raft 2 and an upper raft 3 resting on earthquake-resistant supports 4.

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

[0054] The supports 4 are in the form of pads 6, for example made of reinforced concrete, fixed below to the raft 2, and provided above with an elastically deformable seismic insulator 7, comprising a hooped elastomer 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] Under earthquake, the insulation 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 the damping. They can, if necessary, be associated with additional damping systems, to have additional damping, the supports having essentially an effect on 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 certain supports and overcompresses other supports, causing damage that can be very significant in the structure.

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

[0059] This system 10 comprises a set of holding devices 11 distributed between the rafts 2 and 3 between the earthquake-resistant supports 4.

[0060] For example, as illustrated, there are at least two holding 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 holding devices 11 do not apply any force to the upper raft 3 or apply a force which is low, 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 holding device 11 can be fixed below the lower raft 2 by a joint 12, for example a ball joint, and press against the upper raft 3 by means of an insulator 13, comprising for example a hooped elastomer material. The joint 12 can also be formed from an elastically deformable element allowing a certain angular movement.

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

[0066] In the event of a conventional earthquake, and horizontal vibrations of the structure, the holding devices 11 can accompany, while remaining in the standby state, the movement of the upper raft 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 detachment which affects part of the lower raft 2.

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

[0069] The holding devices 11 which are exposed to this increase in the spacing between the rafts 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 holding device 11 located on the right part of the lower raft 2 thus exerts a force substantially equal to R / 2 in the example considered, which prevents the upper raft 3 from collapsing.

[0071] The moving parts 16 of the devices 11 located around a support 4 together exert a force close to that taken up 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, which greatly limits the stresses and deformations of the upper raft 3, which can thus remain intact with little movement.

[0072] The holding devices 11 are arranged to be triggered only after a displacement of the movable part 16 relative to the body 15 above a given threshold, this threshold being that for which the deformation of the upper raft has no major consequences, this threshold being for example between 5mm and 10mm, for example 5mm.

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

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

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

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

[0077] In the example of Figures 7A and 7B, the movement of the movable part 16 is obtained 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 l of nitrogen compressed to more than 200 bars.

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

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

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

[0081] The movable part 13 may carry an annular seal 22 which is applied to the rib 21 in this state. Alternatively, the seal 22 is carried by the rib. A sealing gasket 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 the pressure.

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

[0085] A shim 30 may be provided between the insulator 13 and the upper raft 3, in order to allow the movable part 16 to press against this raft 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 a resin is injected.

[0087] When the lower raft 2 moves away from the upper raft 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 be applied to the rib 21, and the hydraulic fluid 18 can spread into the chamber 14, as illustrated in [Fig.7B],

[0088] The movable 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 movable part 16.

[0089] The internal section of the pipe(s) 34 supplying the hydraulic fluid 18 to the pressure chamber 14 of the holding device 11 is chosen so that the fluid flow rate is sufficient to obtain the desired reactivity in the event of an earthquake.

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

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

[0092] Secondary pipes 36 constituted for example by 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 of the order of 50 mm. Such a diameter makes it possible to supply for example 20 l of oil in 1 s for a pressure of 200 bars. The primary pipe 35 supplies for example approximately twenty holding devices 11, and its internal diameter is for example greater than or equal to 225 mm.

[0094] The secondary pipes 36 may each be equipped with a controlled valve 37 to close the circuit in the event of a rupture of the hose. This valve 37 may close automatically if the pressure differential upstream and downstream of the valve exceeds a certain value.

[0095] Just as in the example of Figures 7A and 7B, a pressure gauge 38 may be provided to control the supply pressure of the device and a purge valve 39 equipped with a pressure gauge 40 may be provided to monitor the pressure in the chamber 14 outside the seal 22 in the standby state. In the event of an increase in pressure over time linked to a leak, this pressure can be reduced by opening the purge valve 39.

[0096] In the example of [Fig.9], the pressure tank 17 is located in the extension of the chamber 14 and under 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 side wall of the tank 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 guarantee the sealed sliding of the movable part 16 in the body 15.

[0100] The latter can be mounted at its base on an elastically deformable pad 50 which plays the role of an articulation by allowing a slight angular movement of the holding device 11.

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

[0102] The variant illustrated in [Fig. 10] is distinguished from the previous ones by the fact 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] A firing device 62 symbolized by a point in [Fig. 10] moves with the movable part 16 to cause the ignition of the charge 60 after a predefined upward movement stroke, for example approximately 5 mm. This firing device 62 comprises, for example, an electrical contactor moving with the movable part 16, and which, when coming into contact with the charge 60, applies a current causing it to heat up and decompose.

[0104] The holding device 11 may comprise, 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 collapse of the lower base 2, and the firing device 62 can fulfill its function.

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

[0106] One or more additional charges 75 of said solid may be actuated by the continued movement of the firing 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 therein.

[0107] It may be advantageous to provide each holding device 11 with a mechanism which prevents a return movement of the movable part 16, in order to lock the movable 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 produced in various forms, and act for example by a wedging effect or by a ratchet effect.

[0109] As an example, [Fig. 1 1] partially shows a holding device 11 equipped with such a mechanism.

[0110] The non-return mechanism comprises in the example of [Fig.l 1] at least one blocking part 80 which is axially movable upwards against the return action of at least one spring 81.

[0111] This locking part 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 part 86 surrounding the movable part.

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

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

[0114] Locking the moving part 16 in the active state makes it possible to avoid 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 which have just been 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 raft 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 section of the moving part.

[0118] The return of horizontal forces in the zones where the holding 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 beyond the scope of the present invention when it is the opposite or when one side has not moved and the other has descended or risen.

[0120] In conclusion, the invention makes it possible to provide additional earthquake protection to new or existing sensitive structures which have already been subject to earthquake protection consisting of the creation of a double raft with the interposition of earthquake supports between the two rafts.

[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 detachment of an amplitude which can reach several tens of cm.

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

[0123] The fact of articulating the holding devices on the lower raft in the lower part and of 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 vibration modes of the structure.

Claims

Claims

1. Additional seismic protection system (10) for a structure comprising a lower raft (2) and an upper raft (3) with a set of seismic supports (4) between the two, this protection system aiming to protect the structure against the occurrence of a vertical detachment beneath it causing a collapse of the lower raft (2) and the loss of effect of a portion of the seismic supports (4), this additional protection system comprising a set of two-state holding devices (11) arranged between the two rafts, configured to automatically switch, in reaction to the collapse of the lower raft (2), from a retracted standby state where the upper raft (3) is held by the seismic supports (4) to an active deployed state where the force applied by the holding devices (11) on the upper raft (3) is sufficient to compensate for the loss of effect of the supports earthquake-resistant (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 sodium azide.

5. System according to any one of the preceding claims, the holding 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 movable part (16) of each device being urged to come into contact with the upper raft (3) in the standby state, and each device (11) being configured so that the movement of the movable part beyond a predefined stroke in response to the collapse of the lower raft (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 holding devices (11) each comprising at least one seal (22) which is applied in the standby state of the device between the movable 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 movable part (16) in the standby state is limited to a part of the section of the movable part, the seal (22) ceasing to be applied in a sealed manner between the movable part (16) and the body (15) when the movable part has moved a predefined stroke, allowing the pressurized fluid (18) to be applied over the entire section of the movable part (16).

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

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

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

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

13. System according to claims 4 and 6, the movable part (16) driving a firing device (62) which causes the firing 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) urging the movable part (16) to bear against the upper base (3).

15. A system according to any preceding claim, including an attachment to claim 5, comprising an anti-return mechanism (80, 81, 86) preventing reverse movement of the movable part (16) after activation of the holding device.

16. System according to any one of the preceding claims, each holding device (11) being connected by an articulation (12) to the lower raft.

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

18. Method for protecting a structure against the risk linked to the appearance of a fault (F) beneath it, the structure comprising a lower raft (2) and an upper raft (3) with a set of earthquake-resistant supports (4) between the two, method in which an additional protection system (10) as defined in any one of the preceding claims is installed between the rafts.

Images