WO1992013158A2 - A constraint device for parts of viaducts and the like - Google Patents

Abstract

A constraint device (1), adapted for interposition between parts of works, e.g. between two girder members (12, 16) of a viaduct to hold them securely together on the occurrence of such sharp movements as may be brought about by earthquakes, and allow of slow relative movements, as due to thermal expansion, which device has shown to be uncommonly reliable, comprises a cylinder-piston unit (2) having a cylinder (3) wherein a piston (7) defines two oppositely located working chambers (24, 25), a conduit (26) between the chambers (24, 25) provided with a throttle (27), and a gas accumulator (34) formed in the piston (7) and being communicated to one chamber (25) through a passageway (32) provided with a throttle (33).

Description

  
 



  "A constraint device for parts of viaducts and the Like"
 DESCRIPTION
 This invention relates to a constraint device according to the preamble of the main Claim.



   In such construction works as viaducts and the like, erected in seismic areas, a requirement is that the various parts of the works, e.g. girder members thereof, be linked to one another in a suitable way to hold them together on the occurrence of an earthquake, i.e. when imparted jolting movements, while unrestrictedly allowing of slow relative movements thereof to accommodate thermal expansion, for example, without straining.



   Appropriate devices are in use, e.g. such as a cylinder-piston unit which makes a viscous fluid, oil in general, flow through a conduit provided with a throttle.



   The cylinder-piston units currently employed for the purpose are symmetrical double-acting, oil-operated cylinders wherein a certain amount of oil is alternately transferred from one working chamber to the other through a throttled line.



   Such conventional devices, while being satisfactory in several aspects and substantially achieving their objective, still are beset with a drawback originating from temperature range.



   Under a condition of peak summer temperature, the oil expands, and the entire oil-operated cylinder  becomes subjected to excess internal pressure, invariably resulting in oil leakouts past the outer seals and consequent unreliable operation of the device.



   The underlying problem of this invention is to provide a device as specified above, which has such constructional and operational features as to overcome the above-mentioned drawback.



   This problem is solved by a device as indicated in the characterizing part of Claim 1.



   Further features and the advantages of a device according to the invention will become apparent from the following detailed description of a preferred embodiment thereof, given by way of example and not of limitation with reference to the accompanying drawing, whose single
Figure is a part-sectional view showing schematically the inventive device.



   A device 1 according to the invention comprises a cylinder-piston unit 2 having an axis X-X and being filled with a viscous fluid, usually an oil.



   The cylinder-piston unit 2 includes a cylinder 3 having oppositely located cylinder heads 4 and 5.



   A piston 7 can slide, in sealed relationship by virtue of a seal 6, inside the cylinder 3. The piston 7 has a single piston rod 7a being slidable through the head 4 in sealed relationship by virtue of a seal 8  provided.



   The piston rod 7a is terminated with a free end 9 which carries a threaded boss 10. Attached to the threaded boss 10 is a bracket 11 which is associated with a part 12 of a viaduct, e.g. a girder member thereof.



   The head 5 has a central portion 13 whence a threaded boss 14 extends outwards. Attached to the threaded boss 14 is a-bracket 15 associated with another part 16 of the viaduct, such as a girder thereof adjoining the former one.



   From the central portion 13 of the head 5 of the cylinder 3, a cylindrical lug 17 projects inwardly which is made rigid therewith, spans cantilever-fashion the full length of the cylinder 3, and has a free end 18.



   The piston 7 and piston rod 7a have a cylindrical recess 18 whereby they fit over the lug 17 to slide therealong in sealed relationship by virtue of a seal 20.



   The lug 17 has a cylindrical recess 21 which is open at the free end 18.



   A plunger 23 can slide inside the recess 21 in sealed relationship by virtue of a seal 22 provided.



   The piston 7 defines two oppositely located chambers 24 and 25 with different cross-sectioal areas inside the cylinder 3: a chamber 24 of small  cross-section, which locates on the piston rod 7a side, and a large cross-section chamber 25.



   It should be noted that the difference between the chamber cross-sections is a small one, it being equal to the difference of the piston rod cross-section minus the cross-section of the cylindrical recess 19.



   A conduit 26 extends through the piston 7 across the seal 6 to put the chambers 24 and 25 in fluid communication with each other.



   A throttle 27 is arranged on the conduit 26.



  The plunger 23 defines two oppositely located compartments 28 and 29 within the recesses 19 and 21: a compartment 28 located on the side of the piston rod end 9 and a compartment 29 located on the head 5 side.



   The compartment 28 is intended to contain a compressible fluid such as a gas. To this aim, a filler 30 is provided on the end 9 of the piston rod 7a and has a respective closure cap 31.



   The compartment 29 is in fluid communication with the chamber 25 through a passageway 32 along which a throttle 33 is arranged.



   The combination of compartment 28 and compartment 29 provides in practice a gas accumulator, generally indicated at 34, which is formed in the piston 7 of the cylinder-piston unit 2 and communicates to a  chamber 25 of the cylinder-piston unit.



   In operation, temperature changes, e.g. a major rise in temperature, would cause the volume of the oil contained in the chambers 24 and 25, and in the compartment 29, to increase and displace the plunger 23, thereby applying a slight compression to the gas contained in the compartment 28.



   Thus, the oil is allowed to expand unrestrictedly under heat without this entailing any significant increase in the internal pressure of the cylinder-piston unit.



   On the occurrence of a relative movement of the viaduct girders 12 and 16, a relative displacement would take place between the piston 7 and the cylinder 3, resulting in oil being transferred between the chambers 24 and 25 through the conduit 26 and the throttle 27.



   Because of the difference in cross-sectional area between the chambers 24 and 25, excess or short oil would be received or supplied into or from the compartment 29 of the accumulator 34, through the passageway 32 and respective throttle 33, while the gas contained in the accumulator compartment 28 would be slightly compressed or expanded.



   Where said relative movement of the girders is a slow one, as when due to thermal expansion, the device  would oppose no resistance to the works, since the throttles produce no significant pressure step.



   On the other hand, where a girder movement is a sharp one, as induced by an earthquake or any such like dynamic event, the transfer of fluid between the chambers would be resisted by the throttles producing a very large pressure step. Under this circumstance, the device would transfer a very large force, thereby making the girder virtually rigid with its adjacent one.

 

   The device of this invention has shown to be unaffected by temperature changes and quite free of unwanted oil leakouts, thereby performing in a fully reliable manner.



   A further advantage of the device according to the invention is that it can be made uncommonly compact
 l because of the provision therein of a single piston rod.



   A non-negligible advantage is that it is a strong and rugged construction virtually invulnerable to collision shocks from heavy objects, such as may occur during the works emplacement and running.



   Understandably, the device described hereinabove may be altered and modified in many ways by a skilled person in the art to fill specific contingent demands, without departing from the protection scope of the invention as defined in the appended claims. 

Claims

1. A constraint device (1) intended for interposition between parts of works, such as between two girder members (12,16) of a viaduct, to hold them securely together on the occurrence of such sharp movements as would be induced by an earthquake and allow for comparatively slow movements thereof, as brought about by thermal expansion, being of a type which comprises a cylinder-piston unit (2) having a cylinder (3) wherein a piston (7) defines two oppositely located working chambers (24,25), and a conduit (26) between the chambers (24,25) provided with a throttle (27), characterized in that it comprises a gas accumulator (34) communicating to one chamber (25) through a passageway (32) provided with a throttle (33).

2. A constraint device (1) according to Claim 1, characterized in that the gas accumulator (34) is formed within the piston (7).

3. A constraint device according to Claim 2, characterized in that the piston (7) has a single piston rod (7a).

4. A constraint device (1) according to Claim 3, characterized in that said piston rod (7a) has a cylindrical recess (19) whereby it can be fitted, in a sealed and telescopically sliding manner, over a lug (17) made rigid with the cylinder (3).

5. A constraint device (1) according to Claim 4, characterized in that the lug (17) has a cylindrical recess (21) wherein a plunger (23) is movable slidably in sealed relationship which defines a compartment (28) adapted to contain a gas and an oppositely located compartment (29) in communication with one chamber (25) through said passageway (32) provided with a throttle (33), said compartments (28,29) forming in combination the gas accumulator (34).