Brakes – Internal-resistance motion retarder – Having a thrust member with a variable volume chamber
Patent
1998-11-04
2000-11-07
Graham, Matthew C.
Brakes
Internal-resistance motion retarder
Having a thrust member with a variable volume chamber
267224, F16F 922
Patent
active
061422703
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a tie device for use between two elements of a civil engineering structure, and it relates more particularly to a hydraulic force-transmitting device for use between first and second elements of a civil engineering structure, such as a bridge.
Tie devices serve in particular to damp the effects of an earthquake, in particular in bridges, either by dissipating energy, or by transmitting force, during the rapid movements caused by the earthquake.
More particularly, force-transmitting devices enable two structural elements (in a bridge these elements are in general, firstly the deck of the bridge and secondly its foundations, piers, or abutments) to move relative to each other during movements that are mainly due to the effects of temperature variations. In the event of rapid movement, e.g. in the event of an earthquake, the device locks and the two elements are coupled rigidly together.
Most force-transmitting devices are of the hydraulic or oleodynamic type. Such a device essentially consists of a cylinder or actuator provided with two chambers separated by a piston. An orifice of very small diameter enables a fluid to pass from one chamber to the other, thereby enabling the piston to move slowly. In the event of large and rapid stresses causing the piston to move rapidly, it is no longer possible for the fluid to flow, and the device locks.
In that type of device, the piston is generally secured to a rod which passes through the end walls of the cylinder on either side of the piston. Such a rod is connected to one of the elements of the structure, and the cylinder is connected to the other element of the structure. When the length of stroke required to enable the device to operate properly is long, e.g. in long bridges subjected to large temperature variations, the rods are long and their diameter must be increased because there is a possibility that the rod might buckle if it is subjected to a large compression force. That results in an undesirable increase in the overall dimensions of the device.
Another drawback of that oleodynamic type of transmission device is that it is necessary to add an expansion vessel or tank that is capable of absorbing the increase in the volume of the fluid due to temperature increases because, without that precaution, the internal pressure of the device could reach values that are very high. Adding such an external tank to the device, together with its associated hydraulic circuit, is considered to constitute a complication.
Document WO 92/13158 describes such a prior art device in which a moving piston is displaced between the two chambers, one of the chambers being connected to a gas accumulator that is separate from the force transmitter. That device suffers from the drawback of taking up a large amount of space.
An object of the present invention is to provide a tie device, in particular a force-transmitting device, that is compact, that is simple to manufacture and to use, and that operates reliably.
Another object of the present invention is to provide such a device that does not reproduce the above-mentioned drawbacks. In particular, an object of the present invention is to provide a tie device that reduces or eliminates the risk of the rod buckling, and that therefore enables the device to be more compact. Furthermore, another object of the present invention is to provide such device that takes up as little space as possible. In particular, an object of the invention is to avoid adding one or more external hydraulic circuits to the device.
The present invention thus provides a tie device for use between first and second elements of a civil engineering structure, the tie device being suitable for enabling said first and second structural elements to be displaced relative to each other during slow movements, and for preventing at least in part said first and second structural elements from being displaced relative to each other during rapid movements, said device including a cylinder which is stationary relative to said first structural
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patent: 2764404 (1956-09-01), Mercier
patent: 3888436 (1975-06-01), Sealy
patent: 5462141 (1995-10-01), Taylor
Freyssinet International (Stup)
Graham Matthew C.
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