An antiseismic energy dissipator for structures such as viaducts and the like

Abstract: An energy dissipator (2) for interposition between parts of a structure (1), for example, between a support structure (3, 4, 5, 6) and a deck (7) of a viaduct (1), protecting the structure (1) in the event of an earthquake in an effective and consistent manner which conforms to expectations even a very long time after installation and also in the event of repeated operation, comprises an electrical generator (8) interposed between the parts and operated by relative movement between the parts as a result of the earthquake.

Description: The present invention relates to an energy dissipator for interposition between parts of a structure, for example, between a support structure and a deck of a viaduct, to protect the structure in the event of relative movement between the parts as a result of an earthquake. As is known, structures such as, for example, viaducts, have to be protected against damage which could be caused to them by earthquakes. To satisfy this requirement, energy dissipators in which movement between the parts of the structure as a result of an earthquake is resisted by steel elements which undergo considerable deformation when their yield stress is exceeded are known and used extensively. Owing to the magnitude of the deformations undergone, the behaviour of these elements leaves the elastic range and enters the plastic range, giving rise to energy dissipation. Once installed, these energy dissipators have the disadvantage, in use, of behaviour which is often far-removed from the expected behaviour. Moreover, their behaviour is not repeated identically with repeated earthquakes but deteriorates gradually until it is wholly inadequate. Energy dissipators substantially of the hydraulic shock-absorber type have been proposed. These dissipators cannot be left installed for years and years with confidence that they will function as they should when required. On the contrary, they require onerous periodic maintenance operations to replace seals and to top up the oil or to replace them with new improved dissipators, with all of the problems which accompany such operations. From the Japanese Patent JP 01 214646 A an alternative energy dissipator is known. The energy dissipator comprises an electrical generator that is operated by the relative movement between first and second part of a structure. The generator comprises a stator fixed to the first part of the structure, and a rotor, supported in the stator and operatively connected to a mechanical transmission that is fixed to the other part of the structure. Permanent magnets are installed on the stator, whereas elements of ferromagnetic material are mounted to the rotor such that they are facing the magnets. Relative translations between stator and rotor resulting from an earthquake induce currents within the generator which are dissipated. Thus, kinematic energy is transferred to heat. Nevertheless, since the displacements of rotor and stator are identical to the small displacements of the parts of the structure resulting from the earthquake, the amount of dissipated energy is small. Furthermore, the energy dissipator only reacts on unidirectional horizontal displacements in the direction of the axis of the dissipator. Displacements in directions perpendicular to the axis of rotor and stator will produce damages within the dissipator. The problem upon which the present invention is based is that of devising an energy dissipator of the type specified which has structural and functional characteristics such as to overcome the disadvantages mentioned above with reference to the dissipators of the prior art. This problem is solved by a dissipator as defined in claim 1. Further characteristics and the advantages of the dissipator according to the present invention will become clear from the following description of a preferred embodiment thereof, given by way of non-limiting example with reference to the appended drawings, in which: Figure 1 shows a structure incorporating an energy dissipator according to the present invention, Figure 2 shows the dissipator of Figure 1, on an enlarged scale and in section, Figure 3 shows the dissipator of Figure 2, sectioned on the line III-III, With reference to the appended drawings, a structure, generally indicated 1, incorporates an energy dissipator 2 according to the invention. The structure 1 is a viaduct comprising support structures such as a supporting abutment 3, piers 4 and 5, and an opposed supporting abutment 6. A longitudinal deck 7 bears oh the support structures 3, 4, 5 and 6. The dissipator 2, which comprises an electrical generator 8, is interposed between the supporting abutment 3 and the deck 7. The electrical generator 8 which, in practice, is a dynamo, comprises a stator 9 and a rotor 10 in relative rotary motion. The stator 9 has a longitudinal axis X-X. The rotor 10, which has an outside diameter D, is supported for rotation in the stator 9, coaxially therewith, by means of bearings 11 and 12 which can withstand radial forces and axial thrusts. The stator 9 carries permanent magnets 13, whereas the rotor carries elements 14 of ferromagnetic material, preferably windings of conductive material with predetermined resistance. The stator 9 comprises a tubular shell 15 and opposed heads 16 and 17 facing towards the supporting abutment 3 and towards the deck 7, respectively, and is fixed, by the head 16, to the supporting abutment 3, by means of a conventional articulated joint 18 which permits slight inclination of the stator but prevents rotation of the stator about its axis. The rotor 10 is connected to the deck 7 by means of a mechanical transmission 19 which comprises a male-and-female screw coupling 20 of axis X-X. The coupling 20 is reversible, having an efficiency greater than 0.5, for example, an efficiency of 0.8. In particular, the coupling 20 comprises a female-threaded member 21 which is fixed to the rotor 10 and a screw 22 of pitch P, extending through the head 17 and having one end 23 fixed to the deck 7 by means of an articulated joint 24 substantially identical to the articulated joint 18. A protective bellows 25 extends between the end 23 of the screw and the head 17. In the event of an earthquake, a horizontal movement taking place between the supporting abutment 3 and the deck 7 at a given relative velocity brings about an equal axial movement of the screw relative to the stator and to the rotor and consequently a corresponding rotation of the rotor relative to the stator at a corresponding peripheral velocity. This velocity can be made greater than the aforementioned relative velocity by the selection of a large value for the diameter D of the rotor and a small value for the pitch P. Energy dissipation takes place in the electrical generator since the currents induced in the rotor by the magnetic field created by the stator generate heat which is dispersed into the atmosphere. Added to this energy dissipation is the energy dissipation which takes place owing to friction in the male-and-female screw coupling, in a proportion representing the complement of its efficiency to unity, that is, 0.2 in this embodiment. The dimensions of the electrical generator can thus easily be such that it takes care of its portion of the total energy dissipation required, that is, 0.8 in the embodiment described. The main advantage of the dissipator according to the invention lies in its reliability. In fact, it remains installed, ready to operate, for a practically unlimited period without requiring maintenance. Its performance is very consistent even when it is installed in different climatic conditions. A further advantage of the dissipator according to the present invention lies in the fact that there is little difference between its actual behaviour and the theoretical behaviour expected upon the selection of its dimensions. A further advantage of the dissipator according to the present invention lies in the fact that its behaviour is also consistent in the event of repeated operation. Finally, it should be noted that the dissipator according to the present invention can be structurally simple and strong, which is no small advantage for an item which is to be incorporated in large structures on large construction sites.

Claims: An energy dissipator (2) for interposition between a first (3,4,5,6) and a second part (7) of a structure to protect the structure in the event of relative movement between the parts as a result of an earthquake, wherein the energy dissipator comprises an electrical generator operated by said relative movement and comprising a stator (9), having a predetermined axis and fixed to the first part of the structure, a rotor (10), supported in the stator for relative movement with respect to said stator, and operatively connected to a mechanical transmission fixed to the other part of the structure, and permanent magnets fixed to the stator and elements of ferromagnetic material fixed to the rotor, said elements and said magnets facing each other and moving relatively as result of the relative movement between the stator and the rotor, said energy dissipator being characterized in that said mechanical transmission comprises a male-and-female screw coupling included in the rotor and suitable for generating a relative rotation between the stator and the rotor as result of the relative movement between the parts of the structure, said relative rotation resulting in a relative rotation between the permanent magnets and the ferromagnetic material for generating heat by currents induced into the ferromagnetic material, and in that the energy dissipator is operatively connected to said first and second part of the structure by means of a first articulated joint and a second articulated joint, said joints being suitable for permitting slight inclination of the energy dissipator. A dissipator (2) according to Claim 1, characterized in that the male-and-female screw coupling is a reversible coupling (20) which has a screw (22) and a female-threaded member (21), is coaxial with the stator (9) and with the rotor (10), and extends in the direction of the movement. A dissipator (2) according to Claim 2, characterized in that the female-threaded member (21) is fixed to the rotor (10) and the screw (22) is fixed to the other part of the structure.

Inventors: MARIONI AGOSTINO, SILVESTRI ANDREA, UBALDINI MARIO, MARIONI, AGOSTINO, SILVESTRI, ANDREA, UBALDINI, MARIO
Applicants: A L G A APPLIC LAVORAZIONE GIU, A.L.G.A. APPLICAZIONE LAVORAZIONE GIUNTI APPOGGI S.P.A.
Application year: 1997
Main classification: E04H9
IPC codes: E04H9, E01D19