Static structures (e.g. – buildings) – Means compensating earth-transmitted force – Relative motion means between a structure and its foundation
Patent
1998-11-05
2000-08-29
Kent, Christopher T.
Static structures (e.g., buildings)
Means compensating earth-transmitted force
Relative motion means between a structure and its foundation
521678, 188378, E04B 198
Patent
active
061089877
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 damping device for use between first and second elements of a civil engineering structure, such as a bridge.
Tie devices, and in particular damping 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.
There are two main types of damping devices capable of dissipating energy when operating during an earthquake, namely elastoplastic damping devices and oleodynamic damping devices.
Elastoplastic damping devices dissipate energy by alternating plastic deformation of a metal (in general steel) which, beyond a certain displacement, is stressed beyond its elastic limit. Unfortunately such devices are not very efficient, and they have a very short life and must be replaced after a small number of cycles.
An oleodynamic or hydraulic device generally consists of an actuator or cylinder provided with two chambers separated by a piston. The piston is generally connected to one of the structural elements and the cylinder is fixed to the other structural element. The chambers contain a fluid substance which may be a liquid, e.g. oil, or a more viscous material, e.g. a silicone paste. The principle of such an oleodynamic damping device is that, during an earthquake, the fluid can flow from one side of the piston to the other. Energy is dissipated by headloss and results in the fluid being heated. Such oleodynamic damping devices offer high efficiency but they suffer from a certain number of drawbacks. For the device to be effective, the pressure must be as high as possible as soon as the device starts moving. It is very important for pressure to build up rapidly when the displacement stroke must be restricted to low values so to avoid exceeding excessive stresses in certain elements of the structure, in particular the piers of a bridge. For this purpose, some devices are provided with external pressure accumulators so as to maintain at least some minimum pressure on a permanent basis. However, adding such an external pressure accumulator to the device is generally considered to constitute a complication. Other devices are provided with external discharge valves which open passages when the internal pressure increases suddenly. Such valves are expensive and bulky, and they are also considered to constitute complications with their external hydraulic circuits.
Documents U.S. Pat. No. 5,347,771 and GB-1 362 409 disclose respective devices each provided with two one-way valves, each of which operates in a respective flow direction between the two chambers. Those valves complicate manufacture of the device, and therefore increase manufacturing costs. In addition, the operating reliability is not optimum because of the large number of moving parts and because of the sealing problems related thereto.
Furthermore, that type of oleodynamic damping device is generally provided with an orifice of very small diameter enabling fluid to pass from one chamber to the other, thereby enabling the piston to move at low speed. This makes it possible to compensate for the effects of temperature variations. In that type of device, the piston is generally secured to a rod which passes through the end walls of the cylinder or actuator on either side of the piston. Such a rod is connected to one of the elements of the structure, and the cylinder is fixed 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.
Moreover, in that type of oleodynamic damping device, it is necessary
REFERENCES:
patent: 2090751 (1937-08-01), Deutsch
patent: 2309499 (1943-01-01), Chenault
patent: 5347771 (1994-09-01), Kobori et al.
patent: 5462141 (1995-10-01), Taylor
Freyssinet International (Stup)
Kent Christopher T.
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